ANTH 204 – Biological Anthropology

Dr. Alexis Dolphin

Estimated reading time: 61 minutes

Table of contents

Lecture 1: Introduction to Biological Anthropology

What Is Anthropology?

Anthropology is the study of humankind in all times and places. It distinguishes itself from other disciplines that study humans — such as psychology, sociology, or biology — by its insistence on a holistic, comparative, and cross-cultural perspective. Rather than focusing on a single dimension of human experience, anthropology weaves together biology, culture, language, and history to understand what it means to be human.

The field is conventionally divided into four subfields, each approaching the human experience from a different angle. Sociocultural anthropology examines the social institutions, beliefs, and practices of living peoples. Linguistic anthropology investigates the role of language in social life, from how languages evolve to how speech patterns reflect and shape cultural identity. Archaeology recovers and interprets the material remains of past societies — their tools, buildings, refuse, and art — to reconstruct how people lived before written records. Finally, biological anthropology (also called physical anthropology) focuses on the biological dimensions of the human experience: our evolutionary origins, our genetic diversity, our place among the primates, and the ways in which biology and culture interact to shape human populations.

Biological Anthropology

Biological anthropology is concerned with the biological aspects of being human. It studies human evolution, human biological variation, and the biology of other primates. Several major research areas fall under this umbrella:

Paleoanthropology is the study of the human fossil record. Paleoanthropologists recover and interpret the skeletal remains of our ancient ancestors and relatives — the hominins — to reconstruct the path of human evolution over the past six to seven million years. This work requires expertise in anatomy, geology, dating methods, and taphonomy (the study of what happens to organisms after death).

Human biology examines the biological variation found among living human populations. How do populations differ genetically? How do human bodies adapt to different environments — to high altitude, extreme cold, intense solar radiation? Human biologists investigate these questions using tools from genetics, physiology, and epidemiology.

Primatology is the study of our closest living relatives: the non-human primates. By observing chimpanzees, gorillas, orangutans, and other primates in the wild and in captivity, primatologists shed light on the evolutionary roots of human behaviour, social organization, and cognition.

Bioarchaeology applies biological methods to archaeological populations. Bioarchaeologists study human skeletal remains from archaeological sites to learn about past health, diet, disease, migration, violence, and social organization. This subfield bridges archaeology and biological anthropology.

Forensic anthropology applies knowledge of the human skeleton to legal contexts. Forensic anthropologists assist law enforcement by identifying skeletal remains, determining cause of death, and providing expert testimony in court.

The Anthropological Perspective

What unites these diverse subfields is a shared commitment to several core principles. First, anthropology is holistic: it seeks to understand all aspects of human existence, recognizing that biology and culture are deeply intertwined. Second, it is comparative: anthropologists routinely compare across cultures, across species, and across time periods to identify both universal patterns and meaningful variation. Third, it is fieldwork-based: anthropologists go out into the world — to remote villages, archaeological sites, primate habitats, and forensic labs — to gather primary data.

A central theme in biological anthropology is the biocultural approach, which recognizes that human biology and culture are not separate domains but constantly interact. Culture shapes biology (for example, agricultural practices altered human diets and disease patterns), and biology shapes culture (for example, the evolution of language capacity transformed social organization). Understanding this interplay is essential to understanding what it means to be human.

Lecture 2: Science

Chapter 2: The Scientific Method

Science is not a body of facts but a method of inquiry — a systematic way of asking questions about the natural world and testing possible answers. The scientific method provides a framework for producing reliable knowledge through observation, hypothesis formation, testing, and revision.

The process begins with observation: noticing a pattern or phenomenon in the natural world that demands explanation. From observation, a scientist formulates a hypothesis — a tentative, testable explanation for the observed phenomenon. A good hypothesis must be falsifiable: it must make predictions that could, in principle, be shown to be wrong. If a claim cannot be tested or potentially disproven, it falls outside the realm of science.

The next step is testing. Scientists design experiments or collect data to evaluate whether the predictions of the hypothesis hold up. If the evidence supports the hypothesis, it gains credibility — but it is never “proven” in an absolute sense. If the evidence contradicts the hypothesis, it must be revised or abandoned. This iterative cycle of conjecture and refutation is what makes science self-correcting.

Theory vs. Hypothesis

In everyday language, “theory” often means a guess or speculation. In science, however, a theory is something far more substantial: a well-substantiated explanation of some aspect of the natural world that is supported by a large body of evidence and has withstood repeated testing. The theory of evolution, the theory of gravity, and the germ theory of disease are all “theories” in this rigorous sense — not mere guesses, but the best explanations we have, supported by overwhelming evidence.

A hypothesis, by contrast, is a more limited, testable proposition. Hypotheses are the building blocks of theories. When multiple hypotheses are tested and confirmed, and when they cohere into a larger explanatory framework, the result is a scientific theory.

Science and Non-Science

Science is limited to questions about the natural world that can be addressed through observation and testing. It does not — and cannot — address supernatural claims, moral judgments, or questions of meaning and purpose. These are important questions, but they lie outside the scope of scientific inquiry. The distinction between science and non-science (or pseudoscience) is important for biological anthropology, because claims about human origins and human variation have often been co-opted by ideological agendas. Sound science requires evidence, transparency, and a willingness to be proven wrong.

Lecture 3: History of Evolutionary Thought

Pre-Darwinian Ideas

The idea that living things change over time did not spring fully formed from Charles Darwin’s mind. It emerged gradually over centuries, building on contributions from natural history, geology, and philosophy.

Carolus Linnaeus (1707–1778) created the system of biological classification — taxonomy — that we still use today. His Systema Naturae organized all known living things into a nested hierarchy of categories: kingdom, phylum, class, order, family, genus, and species. Linnaeus placed humans squarely within this system, classifying us as Homo sapiens within the order Primates — a revolutionary move that acknowledged our biological kinship with other animals. However, Linnaeus believed that species were fixed and unchanging, created by God in their present forms.

Jean-Baptiste Lamarck (1744–1829) was one of the first naturalists to propose a mechanism for evolutionary change. He suggested that organisms could acquire new traits during their lifetimes in response to environmental demands, and that these acquired characteristics could be passed on to offspring. The classic example is the giraffe: Lamarck proposed that giraffes stretched their necks to reach high leaves, and that this stretching was inherited by the next generation. While Lamarck was wrong about the mechanism, he was right about the fundamental insight that species change over time.

Georges Cuvier (1769–1832) was a pioneering comparative anatomist who recognized that the fossil record showed a succession of different organisms over time. He explained this pattern through catastrophism — the idea that periodic catastrophes (floods, volcanic eruptions) wiped out existing species, which were then replaced by new ones. Cuvier rejected the idea of evolution, but his work on fossils and extinction was crucial to building the case for it.

Charles Lyell (1797–1875) championed uniformitarianism — the principle that the same geological processes operating today (erosion, sedimentation, volcanic activity) also operated in the past, and that the Earth’s features can be explained by slow, gradual change over immense spans of time. This idea of deep time was essential for Darwin, because evolution by natural selection requires vast amounts of time to produce significant change.

Darwin and Wallace

Charles Darwin (1809–1882) and Alfred Russel Wallace (1823–1913) independently arrived at the theory of evolution by natural selection. Darwin’s famous voyage on HMS Beagle (1831–1836) took him to South America, the Galapagos Islands, and around the world, where he observed patterns of variation and distribution that would eventually lead him to his theory.

The key insight came from Thomas Malthus’s Essay on the Principle of Population, which argued that populations tend to grow faster than their food supply, leading to a “struggle for existence.” Darwin realized that in this struggle, individuals with traits that gave them an advantage in their particular environment would be more likely to survive and reproduce, passing those advantageous traits to their offspring. Over many generations, this process — natural selection — could transform populations and give rise to new species.

Darwin published his theory in On the Origin of Species in 1859. The book laid out four key observations and inferences:

  1. Variation: individuals within a population differ from one another in their traits.
  2. Heritability: at least some of this variation is heritable — it can be passed from parents to offspring.
  3. Overproduction: organisms produce more offspring than can survive to reproduce.
  4. Differential survival and reproduction: individuals with traits better suited to their environment are more likely to survive and reproduce — this is natural selection.

Over time, natural selection shifts the characteristics of a population, as advantageous traits become more common and disadvantageous ones become rarer. This is evolution: a change in the inherited characteristics of a population over successive generations.

Natural Selection in Action

Natural selection can be observed in real time. A classic example is the peppered moth (Biston betularia) in industrial England. Before the Industrial Revolution, most peppered moths were light-coloured, camouflaged against lichen-covered tree bark. Dark-coloured moths were rare and easily spotted by predators. As industrial pollution killed the lichen and blackened the tree trunks, the situation reversed: dark moths were now camouflaged, while light moths stood out. The frequency of dark moths increased dramatically — a clear case of natural selection in response to environmental change.

Fitness, in evolutionary terms, does not mean physical strength or health. It refers specifically to an organism’s reproductive success — its ability to survive to reproductive age and produce viable offspring. An organism that is perfectly healthy but produces no offspring has a fitness of zero.

Lecture 4: Heredity and Genetics I

Chapter 3: The Basics of Heredity

To understand evolution, we need to understand heredity — how traits are passed from parents to offspring. The foundation of modern genetics was laid by Gregor Mendel (1822–1884), an Augustinian friar who conducted breeding experiments with pea plants in his monastery garden.

Mendel discovered that inheritance follows predictable patterns. He proposed that traits are controlled by discrete units (which we now call genes), and that each individual carries two copies of each gene — one inherited from each parent. These alternative forms of a gene are called alleles.

Key Mendelian Concepts

Dominant and recessive alleles: when an individual carries two different alleles for a trait, the dominant allele is expressed in the phenotype while the recessive allele is masked. For example, if the allele for brown eyes (B) is dominant over the allele for blue eyes (b), then an individual with one B allele and one b allele (Bb) will have brown eyes.

Homozygous vs. heterozygous: an individual with two identical alleles (BB or bb) is homozygous; an individual with two different alleles (Bb) is heterozygous.

Genotype vs. phenotype: the genotype is the genetic makeup of an individual (e.g., BB, Bb, or bb), while the phenotype is the observable expression of the genotype (e.g., brown eyes or blue eyes). The relationship between genotype and phenotype is not always straightforward — environmental factors can also influence phenotypic expression.

Principle of segregation: during the formation of sex cells (gametes), the two alleles for each gene separate, so that each gamete carries only one allele. When two gametes unite at fertilization, the offspring receives one allele from each parent.

Principle of independent assortment: genes for different traits are inherited independently of one another (assuming they are on different chromosomes). This means that the inheritance of eye colour, for example, does not affect the inheritance of hair colour.

Lecture 5: Heredity and Genetics II

DNA and Chromosomes

The physical basis of heredity is deoxyribonucleic acid (DNA) — a double-stranded molecule shaped like a twisted ladder (the famous double helix, discovered by Watson and Crick in 1953, building on Rosalind Franklin’s X-ray crystallography work). The “rungs” of the ladder are made up of complementary base pairs: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

A gene is a segment of DNA that codes for a specific protein. Proteins are the workhorses of the cell — they serve as enzymes, structural components, hormones, and signaling molecules. The sequence of bases in a gene determines the sequence of amino acids in a protein, which in turn determines the protein’s shape and function.

Chromosomes are structures made of tightly coiled DNA and associated proteins. Humans have 46 chromosomes arranged in 23 pairs. Twenty-two pairs are autosomes (non-sex chromosomes), and one pair consists of sex chromosomes (XX in females, XY in males). One chromosome in each pair is inherited from the mother, the other from the father.

Cell Division

Mitosis is the process of cell division that produces two genetically identical daughter cells. It is responsible for growth, repair, and maintenance of the body. Before mitosis, the cell copies all 46 chromosomes, then divides them equally between two new cells.

Meiosis is a specialized form of cell division that produces gametes (sex cells — sperm and eggs). Unlike mitosis, meiosis involves two rounds of division and produces four cells, each with only 23 chromosomes (half the normal number). This reduction is essential: when a sperm and egg fuse at fertilization, the resulting zygote has the full complement of 46 chromosomes.

Meiosis also introduces genetic variation through two mechanisms: crossing over (where homologous chromosomes exchange segments of DNA) and independent assortment (where chromosomes are randomly distributed to daughter cells). These processes ensure that each gamete is genetically unique, which is why siblings (other than identical twins) are genetically different from one another.

Protein Synthesis

The information encoded in DNA is used to build proteins through a two-step process. Transcription copies the DNA sequence of a gene into a molecule of messenger RNA (mRNA). Translation reads the mRNA sequence and assembles the corresponding chain of amino acids to form a protein. The genetic code is read in units of three bases, called codons, each of which specifies a particular amino acid.

Lecture 6: Heredity and Genetics III

Beyond Mendel: Complex Inheritance

Mendel’s principles describe the simplest cases of inheritance, but many traits do not follow simple dominant-recessive patterns.

Codominance occurs when both alleles in a heterozygote are fully expressed. A classic example is the ABO blood group system: an individual with one A allele and one B allele (genotype AB) expresses both the A and B antigens on their red blood cells, giving them blood type AB.

Incomplete dominance occurs when the heterozygote shows a phenotype intermediate between the two homozygotes. For example, in some plants, crossing a red-flowered plant with a white-flowered plant produces pink-flowered offspring.

Polygenic traits are controlled by multiple genes, each contributing a small effect. Most human traits — including height, skin colour, and body weight — are polygenic. Because many genes are involved, these traits show continuous variation rather than discrete categories. A graph of height in a population, for example, produces a bell curve (normal distribution), not a set of distinct categories.

Pleiotropy occurs when a single gene affects multiple, seemingly unrelated traits. Sickle cell disease is a famous example: a single mutation in the hemoglobin gene produces abnormal red blood cells, which in turn cause a cascade of effects including anemia, organ damage, and pain crises.

Mutations

A mutation is any change in the DNA sequence. Mutations are the ultimate source of all genetic variation — without them, evolution could not occur. They can arise from errors during DNA replication, from exposure to radiation or chemicals, or from the activity of mobile genetic elements.

Most mutations are neutral — they have no effect on the organism’s fitness. Some are harmful, reducing the organism’s ability to survive and reproduce. Rarely, a mutation is beneficial, giving the organism an advantage in its particular environment. Natural selection acts on this variation, favouring beneficial mutations and eliminating harmful ones.

Point mutations change a single base in the DNA sequence. Chromosomal mutations involve larger-scale changes, such as deletions, duplications, inversions, or translocations of chromosome segments.

Lecture 7: Forces of Evolution I

Chapter 4: Mechanisms of Evolution

Evolution is driven by four main forces, each operating at the population level. Together, they explain how and why the genetic composition of populations changes over time.

Natural selection, as discussed above, is the differential survival and reproduction of individuals based on their traits. It is the only force of evolution that is adaptive — that is, it consistently drives populations toward better fit with their environments. Natural selection can take several forms:

  • Directional selection shifts the population toward one extreme of a trait distribution (e.g., larger body size in cold climates).
  • Stabilizing selection favours the average and selects against extremes (e.g., human birth weight — babies that are too large or too small have lower survival rates).
  • Disruptive selection favours both extremes and selects against the average, potentially splitting a population into two distinct groups.

Mutation introduces new genetic variation into a population. As noted above, most mutations are neutral or harmful, but occasionally a mutation produces a new allele that is favoured by selection. The mutation rate is generally low, so mutation alone changes allele frequencies very slowly — but it is essential as the raw material for all other evolutionary forces.

Gene flow (also called migration) is the movement of alleles between populations. When individuals move from one population to another and reproduce, they introduce new alleles into the receiving population and remove alleles from the source population. Gene flow tends to make populations more similar to one another, counteracting the diversifying effects of natural selection and genetic drift.

Lecture 8: Forces of Evolution II

Genetic Drift

Genetic drift is the random change in allele frequencies that occurs in all populations, but is most pronounced in small populations. Unlike natural selection, drift is not adaptive — it does not push populations toward better fit with their environments. Instead, it introduces an element of chance into evolution.

Two special cases of drift are particularly important:

The founder effect occurs when a small group of individuals separates from a larger population and establishes a new population. The new population’s gene pool is a sample of the original — and like any small sample, it may not be representative. Alleles that were rare in the original population may be common in the founders, and vice versa. This can lead to the new population having very different allele frequencies from the parent population.

A population bottleneck occurs when a population is drastically reduced in size by a catastrophic event (disease, famine, natural disaster). The survivors carry only a fraction of the original genetic diversity, and when the population recovers, it may have very different allele frequencies from the pre-bottleneck population.

Hardy-Weinberg Equilibrium

The Hardy-Weinberg principle describes the conditions under which allele frequencies in a population will remain constant from generation to generation — that is, when evolution will not occur. These conditions are:

  1. No natural selection
  2. No mutation
  3. No gene flow
  4. No genetic drift (infinitely large population)
  5. Random mating

In reality, no natural population meets all five conditions, so allele frequencies are always changing — evolution is always occurring. The Hardy-Weinberg model is valuable precisely because it provides a baseline against which to measure evolutionary change. When observed allele frequencies deviate from Hardy-Weinberg expectations, we know that one or more evolutionary forces are at work.

Lecture 9: Species and Speciation

What Is a Species?

The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring, and that is reproductively isolated from other such groups. This definition works well for many organisms, but it has limitations: it does not apply to asexual organisms, and it can be difficult to apply to fossil species or to populations that are geographically separated.

How Do New Species Form?

Speciation is the process by which one species splits into two or more new species. The most common mechanism is allopatric speciation, in which a population is divided by a geographic barrier (a mountain range, a river, an ocean) that prevents gene flow between the two groups. Over time, the separated populations accumulate genetic differences through mutation, natural selection, and drift. If the differences become great enough that the two populations can no longer interbreed — even if the barrier is removed — they have become separate species.

Adaptive radiation occurs when a single ancestral species rapidly diversifies into many new species, each adapted to a different ecological niche. Classic examples include Darwin’s finches in the Galapagos and the lemurs of Madagascar. Adaptive radiation is often triggered by the colonization of a new environment (such as an island) or by the extinction of competitors that opens up new ecological opportunities.

The pace of evolutionary change has been debated. Gradualism holds that evolution proceeds by the slow, steady accumulation of small changes over long periods of time. Punctuated equilibrium, proposed by Niles Eldredge and Stephen Jay Gould, argues that species tend to remain stable for long periods (stasis), punctuated by brief episodes of rapid change — often associated with speciation events. The fossil record often shows patterns more consistent with punctuated equilibrium than with strict gradualism.

Lecture 10: Primates I

Chapter 5: The Living Primates

Humans are primates, and understanding our primate relatives is essential for understanding ourselves. The order Primates includes roughly 500 living species, from tiny mouse lemurs to massive gorillas. What unites this diverse group is a set of shared characteristics, most of which are adaptations to life in the trees (arboreal life).

Primate Characteristics

Grasping hands and feet with opposable thumbs (and often opposable big toes) allow primates to grip branches securely. Most primates have nails rather than claws, and sensitive tactile pads on their fingertips.

Forward-facing eyes provide stereoscopic (binocular) vision — the ability to perceive depth. This is critical for judging distances when leaping between branches. Primates also tend to have enhanced colour vision compared to most other mammals.

Large brains relative to body size, particularly in the neocortex, are associated with complex social behaviour, learning, and problem-solving.

Flexible limb structure allows a wide range of motion at the shoulder and hip joints. Most primates can rotate their forearms and have a high degree of manual dexterity.

Reduced reliance on smell (olfaction) compared to other mammals, with a corresponding increase in reliance on vision.

Extended life histories: primates tend to have long gestation periods, produce few offspring at a time, invest heavily in each offspring, and have long periods of juvenile dependency and overall lifespan.

Primate Taxonomy

The order Primates is divided into two major groups:

Strepsirrhines (“wet-nosed” primates) include lemurs, lorises, and galagos (bushbabies). They tend to retain more ancestral mammalian features: a moist rhinarium (nose pad), a greater reliance on smell, and in some species, a dental comb used for grooming. Many are nocturnal.

Haplorhines (“dry-nosed” primates) include tarsiers and the anthropoids (monkeys, apes, and humans). Haplorhines have dry noses, greater reliance on vision, and generally larger brains. The anthropoids are further divided into:

  • Platyrrhines (New World monkeys): found in Central and South America, with flat noses, widely spaced nostrils, and often prehensile tails. Examples include spider monkeys, howler monkeys, and marmosets.
  • Catarrhines (Old World monkeys, apes, and humans): found in Africa, Asia, and (historically) Europe, with narrow noses and downward-facing nostrils. No catarrhine has a prehensile tail. This group includes:
    • Cercopithecoids (Old World monkeys): baboons, macaques, colobus monkeys
    • Hominoids (apes and humans): gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans

Lecture 11: Primates II

The Apes

The hominoids (superfamily Hominoidea) are distinguished from monkeys by several features: they are generally larger, have no tails, have more flexible shoulder joints, and have larger brains relative to body size.

Gibbons and siamangs (family Hylobatidae) are the “lesser apes,” found in Southeast Asian forests. They are the smallest hominoids and are famous for their spectacular brachiation — swinging hand-over-hand through the treetops at high speed. They are monogamous and highly territorial, defending their territories with elaborate vocal duets.

Orangutans (Pongo) are found in the rainforests of Borneo and Sumatra. They are the largest arboreal mammals and are largely solitary — an unusual trait among primates. Males are much larger than females (pronounced sexual dimorphism). Orangutans are highly intelligent and have been observed using tools in the wild.

Gorillas (Gorilla) are the largest living primates, found in the forests of central Africa. They live in groups typically led by a dominant silverback male. Despite their imposing size, gorillas are primarily herbivorous, feeding mainly on leaves, stems, and shoots. They are largely terrestrial and move by knuckle-walking.

Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are our closest living relatives, sharing approximately 98–99% of our DNA. Chimpanzees live in large, complex social groups in the forests and woodlands of equatorial Africa. They are omnivorous, occasionally hunting and eating meat. Chimpanzees are famous for their tool use, their complex social politics, and their capacity for both cooperation and aggression. Bonobos, found only in the Democratic Republic of Congo, are similar in many ways but tend to be less aggressive and more egalitarian, with sexual behaviour playing a prominent role in social bonding and conflict resolution.

Primate Locomotion

Primates move through their environments in diverse ways:

  • Quadrupedalism: walking on all fours, the most common form of primate locomotion (most monkeys)
  • Knuckle-walking: a specialized form of quadrupedalism in which the animal walks on the knuckles of the hands (gorillas, chimpanzees)
  • Brachiation: swinging hand-over-hand beneath branches (gibbons)
  • Vertical clinging and leaping: clinging to vertical tree trunks and leaping between them (tarsiers, some lemurs)
  • Bipedalism: walking upright on two legs — unique to humans among living primates

Lecture 12: Primate Behaviour I

Chapter 6: Primate Behaviour

Studying primate behaviour helps us understand the evolutionary roots of human social life. Primates are among the most social of all mammals, and their social systems are remarkably diverse.

Why Be Social?

Living in groups provides several benefits: protection from predators (more eyes to spot danger, safety in numbers), access to food (cooperative foraging, defense of food resources), and access to mates. However, group living also has costs: increased competition for food and mates, greater risk of disease transmission, and heightened social stress.

Primate Social Systems

Primate social organization varies widely:

  • Solitary: some prosimians, such as orangutans, are largely solitary, with males and females coming together only to mate.
  • Pair-bonded: some primates, including gibbons and many New World monkeys (e.g., titi monkeys), form long-term pair bonds.
  • One-male, multi-female groups: a single dominant male monopolizes mating access to several females. Examples include gorillas and some langurs.
  • Multi-male, multi-female groups: large groups with multiple adults of both sexes. This is the most common primate social system, found in baboons, macaques, and chimpanzees.

Dominance and Social Hierarchies

Most primate groups have dominance hierarchies — ranking systems in which some individuals have priority of access to resources (food, mates, resting spots) over others. Dominance is typically established and maintained through a combination of aggression, intimidation, alliance-building, and reconciliation.

In many species, males compete for dominance through physical contests, while females inherit their rank from their mothers (matrilineal rank inheritance). High-ranking individuals enjoy tangible benefits — better nutrition, more mating opportunities, lower stress — but maintaining dominance also exacts costs in terms of energy and risk of injury.

Lecture 13: Primate Behaviour II

Communication

Primates communicate through a rich repertoire of vocalizations, facial expressions, body postures, and gestures. Vervet monkeys, for example, produce distinct alarm calls for different predators (eagles, leopards, snakes), and listeners respond with appropriate evasive behaviour — suggesting that primate calls can convey specific, referential information.

Grooming is one of the most important social behaviours in primates. It serves a hygienic function (removing parasites and debris from fur), but more importantly, it is a powerful tool for social bonding. Primates spend a disproportionate amount of time grooming close allies and kin, and being groomed reduces stress hormones. Grooming is often “traded” for other social benefits, such as support during conflicts.

Reproduction and Parenting

Primate reproductive strategies vary widely, but several patterns are common. Most primates have long gestation periods, produce single offspring (rather than litters), and invest heavily in each infant. Infants are typically carried by the mother and nursed for extended periods.

Female choice plays an important role in primate mating systems. Females often prefer males who are dominant, who provide protection, or who demonstrate good genes. In some species, females mate with multiple males — a strategy that may reduce the risk of infanticide by making paternity uncertain.

Infanticide — the killing of infants by adult males — has been documented in several primate species, including langurs, gorillas, and chimpanzees. When a new male takes over a group, he may kill the existing infants, which causes the mothers to resume ovulation sooner and allows the new male to sire his own offspring. This grim behaviour is understood as a reproductive strategy shaped by natural selection.

Lecture 14: Primate Behaviour III

Intelligence and Culture

Primates are among the most intelligent animals on Earth. Their large brains — particularly the neocortex — support complex cognitive abilities including problem-solving, memory, self-awareness, and social intelligence.

Tool use has been documented in many primate species. Chimpanzees are the most prolific non-human tool users: they use sticks to fish for termites, stones to crack nuts, and leaves as sponges to soak up water. Some populations have developed distinct tool-use traditions that are passed from generation to generation through social learning — a phenomenon that many researchers call culture.

Culture, in the anthropological sense, refers to behaviour that is learned socially (rather than genetically inherited) and that varies between groups. Different chimpanzee populations in Africa have different tool-use traditions, different grooming styles, and different social customs — even when they live in similar environments. This suggests that these behaviours are transmitted culturally rather than determined by genes or ecology.

Language experiments with great apes have shown that chimpanzees, bonobos, and gorillas can learn to use symbols (including sign language and lexigrams) to communicate with humans. While no non-human primate has demonstrated the full complexity of human language — including syntax, recursion, and open-ended generativity — these studies reveal impressive cognitive abilities and blur the line between human and non-human communication.

Lecture 15: Primate Conservation

Chapter 7: Primate Conservation (pp. 151–161)

Many primate species are endangered or critically endangered. The primary threats to primate survival are:

Habitat destruction: deforestation for agriculture, logging, and urban expansion is the single greatest threat to primates worldwide. As forests shrink, primate populations become fragmented, isolated, and increasingly vulnerable to extinction.

Hunting: primates are hunted for food (the bushmeat trade), for traditional medicine, and for the pet trade. In some regions, hunting pressure is intense enough to threaten species with extinction even when suitable habitat remains.

Climate change: shifting temperature and rainfall patterns alter the distribution of forests and food resources, forcing primates to adapt, migrate, or perish.

Conservation efforts include habitat protection (national parks and reserves), anti-poaching enforcement, captive breeding programs, community-based conservation, and ecotourism that provides economic incentives for local people to protect primate habitats.

Lecture 16: Primate Evolution and Proto-Hominins

Chapters 7 (151–161) and 9

Understanding primate evolution requires understanding the geological and environmental context in which it occurred. The fossil record reveals a long succession of primate forms, from the earliest primate-like mammals of the Paleocene to the diverse array of primates living today.

Dating Methods

Recovering fossils is only the first step — we also need to know how old they are. Dating provides the time axis that allows us to arrange fossils in chronological order and understand the pace of evolutionary change.

Relative dating tells us whether one fossil is older or younger than another, without assigning a specific age. The most basic method is stratigraphy — the study of rock layers (strata). The law of superposition states that, in undisturbed sedimentary sequences, deeper layers are older than layers above them. Relative dating also includes biostratigraphy (using the known ranges of fossil species to date layers) and fluorine dating (measuring the amount of fluorine absorbed by buried bones).

Absolute dating (also called chronometric dating) assigns a specific age (or age range) to a fossil or geological layer. Radiometric dating methods measure the decay of radioactive isotopes. Potassium-argon (K-Ar) dating is widely used for volcanic rocks and can date materials millions of years old. Carbon-14 dating is useful for organic materials up to about 50,000 years old. Other methods include thermoluminescence, electron spin resonance, and paleomagnetism.

Geological Time Scale

Date (mya) Epoch Event Key Taxa
65–54 Paleocene 1st primate-like mammals Plesiadapiforms
55–34 Eocene 1st true primates Adapids, Omomyids
34–24 Oligocene 1st anthropoids Aegyptopithecus
24–5 Miocene Adaptive radiation of hominoids Proconsul, Sivapithecus, Gigantopithecus
5–1.7 Pliocene Adaptive radiation of hominins Ardipithecus, Australopithecus, Paranthropus
1.7–0.01 Pleistocene Evolution of genus Homo Homo
0.01–present Holocene Agriculture, industry Homo sapiens

Proto-Hominins

Hominins are defined as humans and our bipedal ancestors and relatives — all species on the human lineage after the split from our last common ancestor with chimpanzees. DNA and fossil evidence place this divergence at approximately 6–7 million years ago (mya).

The earliest proto-hominins are fragmentary and controversial:

Sahelanthropus tchadensis (~7–6 mya, Chad) is known from a single cranium nicknamed “Toumaï.” Its foramen magnum (the hole where the spinal cord exits the skull) is positioned somewhat forward, suggesting possible bipedality, but this interpretation is debated.

Orrorin tugenensis (~6 mya, Kenya) is known from fragmentary postcranial remains, including femora (thighbones) that show features consistent with bipedal locomotion.

Ardipithecus includes two species: Ar. kadabba (~5.8–5.2 mya) and Ar. ramidus (~4.4 mya). “Ardi,” a partial skeleton of Ar. ramidus, reveals a mosaic of primitive and derived features — including an opposable big toe (suggesting arboreal climbing) alongside pelvic features suggesting some degree of bipedality. Ardipithecus appears to have been a woodland-dwelling creature, challenging the older idea that bipedalism evolved on the open savanna.

Lecture 17: Early Hominins

The Australopithecines

The australopithecines are a diverse group of hominins that lived in Africa from roughly 4.2 to 1.0 mya. They were bipedal but retained some arboreal adaptations, had small brains (roughly chimp-sized), and had large teeth and jaws adapted for processing tough, fibrous foods.

Australopithecus anamensis (~4.2–3.9 mya, Kenya and Ethiopia) is one of the earliest known australopithecines. Its tibial (shinbone) features indicate bipedal locomotion, while some dental features are quite primitive.

Australopithecus afarensis (~3.9–2.9 mya, East Africa) is one of the best-known early hominins, thanks to the famous partial skeleton “Lucy” (discovered by Donald Johanson in 1974 in Hadar, Ethiopia) and the Laetoli footprints (preserved footprints in volcanic ash in Tanzania, ~3.6 mya). Au. afarensis was clearly bipedal, as evidenced by the anatomy of the pelvis, knee, and foot, and by the Laetoli footprints. However, the curved finger and toe bones suggest that it still spent significant time in the trees. Brain size averaged about 430 cc — similar to a chimpanzee. Au. afarensis showed considerable sexual dimorphism, with males significantly larger than females.

Australopithecus africanus (~3.0–2.0 mya, South Africa) was the first australopithecine discovered, by Raymond Dart in 1924 (the Taung Child). It was somewhat more derived than Au. afarensis, with a slightly larger brain and smaller teeth, but was still clearly a small-brained biped.

The Robust Australopithecines (Paranthropus)

The robust australopithecines — now often placed in the genus Paranthropus — were characterized by massive jaws, enormous molars, and prominent sagittal crests (bony ridges on top of the skull for the attachment of powerful chewing muscles). These features suggest a diet focused on hard, tough foods like seeds, nuts, and roots.

Paranthropus aethiopicus (~2.5 mya, East Africa) is the earliest robust form, known primarily from the “Black Skull” (WT 17000).

Paranthropus boisei (~2.3–1.2 mya, East Africa) had the most extreme robust features — massive jaws and the largest molars of any hominin. It was discovered by Mary Leakey at Olduvai Gorge in 1959 and originally nicknamed “Nutcracker Man.”

Paranthropus robustus (~1.8–1.0 mya, South Africa) was somewhat less extreme than P. boisei but still had very large teeth and powerful jaws.

The robust australopithecines represent an evolutionary dead end — they went extinct without leaving descendants. Their heavy-duty chewing apparatus represents a different adaptive strategy from the one that led to the genus Homo.

The Grandmother Hypothesis

The grandmother hypothesis proposes that human female longevity past reproductive age (menopause) evolved because post-reproductive women could increase their inclusive fitness by helping to raise their grandchildren. In this view, female fertility declines relatively early compared to non-human primates, and females redirect their reproductive efforts into existing offspring and their offspring’s children, providing beneficial resources and caregiving. This creates indirect benefits for the grandmother’s reproductive fitness, potentially explaining why selection has favoured extended post-reproductive lifespan in humans.

Lecture 18: Early Homo

Chapter 10: The Genus Homo

The emergence of the genus Homo marks a major transition in human evolution. Compared to the australopithecines, members of the genus Homo are characterized by larger brains (over 600 cc), flatter faces, smaller teeth, greater reliance on tools (culture), use of fire, and eventual migration out of Africa into the Old World.

Homo habilis

The first members of the genus Homo were discovered in 1960 by Louis and Mary Leakey at Olduvai Gorge, Tanzania. Found in the same deposits as Paranthropus boisei, these fossils dated to approximately 1.9 mya and were associated with stone tools nearby — hence the name Homo habilis (“handy man”). Possible H. habilis sites have been dated as far back as 2.4 mya.

Homo habilis (2.4–1.4 mya) retained some slight arboreal adaptations in its hands. Its derived traits included an average cranial capacity of approximately 629 cc (range 510–750 cc), enlarged frontal and parietal lobes (areas associated with language), a less prognathic (protruding) face, a parabolic dental arcade, and reduced molar size. The holotype specimen is KNM-ER 1813.

One Species or Two?

The discovery of KNM-ER 1470 — a skull with a larger cranial capacity (~750 cc) and a flatter, less robust face — raised the question of whether more than one species of early Homo existed. This specimen became the holotype of Homo rudolfensis, found at Koobi Fora, Kenya, and dated to approximately 1.8 mya (possibly 2.4 mya). The differences between H. habilis and H. rudolfensis could represent separate species, sexual dimorphism within a single species, or simply variation within a single population. The question of which species is ancestral to later Homo remains debated.

Behavioural Adaptations: The First Stone Tools

The Oldowan industry represents the earliest known stone tool technology. The oldest Oldowan tools come from Gona, Ethiopia, dated to 2.6 mya, placing them in the Lower Paleolithic (also known as the Old Stone Age, 2.5 mya to 200 kya).

Oldowan tools are simple pebble tools and choppers made of quartz, chert, and flint, produced by a percussion technique — striking one stone (the hammer stone) against another (the core) to remove sharp flakes. Both the flakes and the modified cores were used as tools. Quarrying sites have been identified in East Africa, and Oldowan tools are often found near animal bones bearing cut marks — evidence that early Homo was processing animal carcasses, whether through hunting or scavenging.

Lecture 19: Homo erectus

Chapter 10 (continued)

Homo erectus represents a major advance over earlier Homo. This species was the first hominin to leave Africa, the first to use fire systematically, and the first to show body proportions essentially modern in their limb ratios.

Discovery and Distribution

The first Homo erectus fossils were discovered by Eugène Dubois in Java, Indonesia in 1891 — originally named Pithecanthropus erectus (“upright ape-man”). Subsequently, H. erectus fossils have been found across Africa, Asia, and possibly Europe, including important sites at Olduvai Gorge (Tanzania), Koobi Fora and Nariokotome (Kenya), Zhoukoudian (China — the famous “Peking Man”), Sangiran and Trinil (Java), Dmanisi (Georgia), and Tighenif (Algeria).

The Nariokotome Boy (also known as Turkana Boy, KNM-WT 15000) is the most complete early human skeleton ever found — a juvenile H. erectus (or H. ergaster) dating to approximately 1.6 mya. Analysis of this skeleton revealed that H. erectus had a body plan much like modern humans: tall, with relatively long legs and short arms, indicating full commitment to terrestrial bipedalism and efficient long-distance walking and running.

One Species or Two? Or More?

Some researchers recognize regional variants of H. erectus as separate species: H. ergaster (Africa), H. erectus in the strict sense (Asia), and H. georgicus (Dmanisi, at the juncture of Eastern Europe and Western Asia). Others lump all these forms into a single, geographically variable species. The Dmanisi specimens are particularly interesting because they are among the earliest hominins found outside Africa (~1.8 mya) and show a surprising range of variation, with relatively small brains (~600–775 cc) — challenging the idea that large brains were a prerequisite for leaving Africa.

Anatomy

Homo erectus had a cranial capacity ranging from about 600 to 1,250 cc (averaging ~900 cc), with a long, low cranial vault, a prominent brow ridge (supraorbital torus), a receding forehead, a projecting face, and robust postcranial bones. The dental arcade was parabolic, and the teeth were smaller than in earlier hominins.

Cultural Advances

Homo erectus is associated with the Acheulean stone tool industry, characterized by large, carefully shaped hand axes (bifaces) — a significant technological advance over the simpler Oldowan choppers. Acheulean tools first appear around 1.7 mya in Africa and persist until roughly 200 kya.

Evidence for the controlled use of fire by H. erectus includes burned bones, charcoal, and hearth-like structures at several sites. Fire provided warmth, protection from predators, light, and the ability to cook food — cooking may have been a key innovation, making food more digestible and freeing up energy for brain growth.

Homo floresiensis

In 2003, a remarkable discovery was announced from Liang Bua cave on the island of Flores, Indonesia: a diminutive hominin standing only about 1 metre tall, with a brain size of just 426 cc. Initially dated to 18–95 kya, the age is now thought to be closer to 50 kya. The holotype specimen is LB1.

Homo floresiensis displays a puzzling combination of primitive and derived traits. Primitive features (like australopithecines) include a small brain, small stature, and primitive wrist bones and body proportions. Derived features (like H. erectus) include the shape of the brain, facial morphology, and dental characteristics. H. floresiensis was found with stone tools and butchered animal remains.

Hypotheses about this species have included microcephaly (a pathological condition), insular dwarfism (the evolutionary reduction in body size that sometimes occurs in island populations), and a separate lineage from a very early, small-bodied hominin ancestor. DNA analysis has been attempted but has not yet been successful.

Stone Age Culture Periods

The cultural periods of the Stone Age overlay the geological epochs:

The Paleolithic (Old Stone Age, 2.6 mya–10 kya) is divided into Lower (Oldowan and Acheulean), Middle (Mousterian and other prepared-core technologies), and Upper (blade technologies and sophisticated tool kits). The Mesolithic (Middle Stone Age) is a transitional period. The Neolithic (New Stone Age, beginning ~10 kya) is associated with the origin of agriculture. Note that the Pleistocene (geological) and Paleolithic (cultural) have different start dates (1.7 mya and 2.6 mya respectively) but both end at roughly 10 kya.

Lecture 20: Neandertals

Chapter 11

Neandertals (Homo neanderthalensis) are among the best-known and most intensively studied of all fossil hominins. They were discovered in 1856 in the Feldhofer Cave in the Neander Valley (Neander Tal), Germany — the original find consisted of a calvarium (skullcap), ribs, pelvis, and limb bones.

Neandertals lived in Europe, the Middle East, and Central Asia from approximately 250,000 to 25,000 years ago. Major Neandertal sites include La Chapelle-aux-Saints, La Ferrassie, and Le Moustier (France); Spy and Engis (Belgium); Krapina (Croatia); Shanidar (Iraq); Tabun, Amud, and Kebara (Israel); and Gibraltar.

Neandertal Morphology

Neandertals were stocky, powerfully built, and well-adapted to cold climates. Compared to modern humans, they had:

  • Flatter, bigger craniums with an average cranial capacity of about 1,500 cc — actually larger than the modern human average
  • More massive brow ridges
  • Larger nasal cavities — possibly an adaptation for warming and moistening cold, dry air
  • Bigger shoulder joints, larger, broader rib cages
  • Bigger elbow and hip joints
  • Shorter forearms and shorter, more flattened tibias
  • Broader hips and larger, thicker patellae
  • Bigger ankle joints
  • An average height of about 165 cm (5’5”) for males — shorter than modern human males but extremely robust

Their body proportions follow Allen’s rule and Bergmann’s rule: in cold climates, natural selection favours shorter limbs and stockier bodies (lower surface-area-to-volume ratio) to conserve heat.

Neandertal Behaviour

Neandertals were sophisticated beings. They produced Mousterian stone tools (Middle Paleolithic), characterized by the Levallois technique — a prepared-core method that allowed the knapper to predetermine the shape of the flake before striking it from the core.

Evidence for Neandertal cultural complexity includes:

  • Burial of the dead: multiple Neandertal burials have been documented, some with possible grave goods
  • Use of fire: systematic and widespread
  • Hunting: Neandertals were skilled hunters of large game, including mammoths, bison, and deer
  • Use of medicinal plants: analysis of dental calculus has revealed evidence of plant consumption, including possible medicinal species
  • Symbolic behaviour: limited evidence of personal ornamentation (eagle talons, pigment use) in late Neandertal sites

The Fate of the Neandertals

Neandertals went extinct approximately 45 kya in the Middle East and 30 kya in Europe. Several factors likely contributed to their demise:

The last glacial maximum saw the full extension of ice sheets by about 26.5 kya, bringing deteriorating climatic conditions and diminishing food resources. Anatomically modern Homo sapiens arrived in Europe by 40 kya, with an estimated ten-fold population increase that may have out-competed the Neandertals for resources.

The Lagar Velho skeleton (Lagar Velho 1), a 4-year-old child from Portugal dated to 24.5 kya, has been interpreted by some as a possible Neandertal–modern human hybrid, showing a mosaic of features from both groups.

Neandertal DNA

Ancient DNA (aDNA) analysis, pioneered by Svante Pääbo and colleagues, has revealed that Neandertals interbred with modern humans. Most people of non-African descent carry approximately 1–4% Neandertal DNA. This interbreeding likely occurred when modern humans expanded out of Africa and encountered Neandertals in the Middle East and Europe.

Lecture 21: Archaic Hominins and Homo heidelbergensis

Emergence of Archaic Hominins

Archaic hominins emerged by approximately 800–500 kya and represent a transitional grade between Homo erectus and Homo sapiens. They display a mosaic of H. erectus and H. sapiens traits.

Primitive traits (from H. erectus) include large brow ridges, a receding forehead, and a long-low cranium. Derived traits (toward H. sapiens) include smaller teeth, increased cranial capacity (~1,200 cc), and some regionally specific features.

Archaic hominin fossils have been found across Africa, Europe, and Asia. The same question that arises with H. erectus applies here: are these regional variants of a single species, or should they be split into multiple species?

African Archaic Hominins

Key African archaic hominin sites include:

Bodo, Ethiopia (600 kya): a cranium showing a mix of H. erectus features (low vault, sloping forehead, heavy brow ridge) and H. sapiens features (cranial capacity of 1,250 cc).

Kabwe (Broken Hill), Zambia (125 kya): similarly mosaic morphology.

European Archaic Hominins

Sima de los Huesos (“Pit of Bones”) in the Atapuerca region of Spain (300 kya) has yielded the remains of 28 individuals, including 3 complete skulls. They show arched brow ridges and projecting faces. A 2016 aDNA analysis found them to be genetically similar to Neandertals, supporting the lineage: H. erectus → Sima de los Huesos archaics → Neandertals.

Asian Archaic Hominins

Dali, China (200 kya): a cranium with H. erectus traits (low vault, massive brow ridges) combined with H. sapiens traits (smaller, flatter face). Its ultimate fate is uncertain — possibly replaced by Euro-African forms, though complex patterns of interbreeding are emerging.

Homo heidelbergensis

Some researchers recognize a distinct species, Homo heidelbergensis, for archaic hominins found in Africa, Europe, and Western Asia during the Middle Pleistocene (780–125 kya). In this view:

  • In Europe, the Middle East, and Asia, H. heidelbergensis is ancestral to Neandertals and Denisovans
  • In Africa, H. heidelbergensis is ancestral to anatomically modern Homo sapiens

Others prefer to lump all archaic hominins as either archaic Homo sapiens or Homo heidelbergensis without distinguishing between them. The taxonomy remains actively debated.

Denisovans

The Denisovans are known primarily from DNA extracted from a finger bone and teeth found in Denisova Cave, Siberia (~50 kya). Genomic analysis revealed them to be a distinct group, more closely related to Neandertals than to modern humans. Like Neandertals, Denisovans interbred with modern humans — modern Melanesians and some Southeast Asian populations carry approximately 3–5% Denisovan DNA.

Lecture 22: Anatomically Modern Homo sapiens

Chapter 12

AMHS: Definition and Traits

Anatomically modern Homo sapiens (AMHS) appeared approximately 200–150 kya and persist to the present. Their derived traits include:

  • A higher, rounded cranium with the back rounded rather than angulated
  • Average cranial capacity of approximately 1,350 cc
  • A vertically oriented forehead (no receding)
  • Small brow ridges
  • A smaller, flatter face
  • Smaller teeth
  • A protruding chin (mental eminence) — unique among hominins
  • A lightly built, more gracile postcranial skeleton

Origin of AMHS: Three Models

Three main models have been proposed to explain the origin of anatomically modern humans:

a) Out-of-Africa / Replacement Model: AMHS evolved in Africa 200–150 kya, then spread throughout Africa and into Europe and Asia, replacing pre-existing archaic populations with no or little interbreeding. This model predicts that all modern human genetic diversity traces back to a recent African origin.

b) Assimilation Model (similar to Clinal Replacement): AMHS evolved in Africa 200–150 kya, then spread into Europe and Asia, where they interbred with small archaic populations, genetically swamping them over time. This model predicts mostly African ancestry with small contributions from archaic populations.

c) Multiregionalism: Modern humans evolved from archaic humans in several regions of the Old World (Africa, Europe, Asia) over almost 2 million years (from H. erectus onward), with extensive gene flow between regions maintaining populations as a single species. This model predicts deep genetic roots in multiple regions.

Current evidence — especially from ancient DNA — best supports the Assimilation model: AMHS originated in Africa and spread globally, but interbred with Neandertals, Denisovans, and possibly other archaic populations along the way.

Key Fossil Sites

The earliest AMHS fossils come from Africa:

  • Omo Kibish, Ethiopia (~195 kya)
  • Herto, Ethiopia (~160 kya)
  • Jebel Irhoud, Morocco (~300 kya — controversial, possibly archaic rather than fully modern)

The first AMHS in Europe are documented at Peștera cu Oase, Romania (42,000–37,000 years ago), where 3 individuals were found. Remarkably, Oase 1 and Oase 2/3 carry 6–9% Neandertal DNA, indicating that interbreeding with Neandertals occurred relatively recently in their ancestry.

Emergence of Modern Behaviour

The transition from the Middle to Upper Paleolithic (by 40 kya in Africa) is marked by the emergence of behavioural modernity — the suite of behaviours that characterize modern humans: abstract thought, language, symbolism, and complex social relationships.

Evidence of behavioural modernity includes:

  • Diverse toolkits: bone and antler needles, bone points and harpoons, composite tools, and blade technology
  • Personal adornment: pierced shell beads, incised ochre, pendants, and ochre-stained shells for preparing pigment
  • Cave painting and rock art: found in Europe, Africa, and Australia
  • Bone, ivory, or clay female “Venus” figurines: over 200 found, dating from 40–11 kya, primarily in Central Europe and Russia
  • Burials with increasing evidence of ritual and grave goods

Lecture 23: Contemporary Human Variation

Chapters 14 (pp. 331–337) and 13

How Do We Understand Phenotypic Variation?

Homo sapiens is a relatively homogenous species genetically — far less genetically diverse than chimpanzees, for example. Yet we are not identical. Thousands of genes produce countless phenotypic outcomes, and certain phenotypes are more common in some populations than in others. Many of these differences are the result of local adaptations to different environments, shaped by natural selection (and sometimes by genetic drift).

How We Vary: Clinal Variation

Clinal variation describes a pattern in which the frequency of a trait changes gradually across a geographic area. A cline has no discrete beginning or end — it is a matter of “more or less” rather than “either/or.” Skin colour, for example, varies clinally with latitude: populations closer to the equator tend to have darker skin, while populations at higher latitudes tend to have lighter skin. This gradient reflects adaptation to different levels of ultraviolet (UV) radiation.

Adaptations to Climate: Ecogeographical Rules

Two classic ecogeographical rules describe patterns of body size and shape in relation to climate:

Bergmann’s rule: among mammals of the same shape, smaller individuals have a higher surface-area-to-volume ratio and lose heat more quickly. Therefore, cold climates tend to favour larger, heavier body size (lower SA/V ratio conserves heat), while warm climates favour smaller, lighter body size.

Allen’s rule: among mammals of the same size/volume, those with a more linear shape (longer appendages) have a higher surface-area-to-volume ratio and lose more heat. Cold climates favour shorter appendages, while warmer climates favour longer appendages.

In humans, these rules are broadly supported: populations in cold climates (e.g., Inuit) tend to have short limbs and stockier bodies, while populations in hot climates (e.g., Nilotic peoples of East Africa) tend to have long, slender limbs and lighter, linear bodies. There are, however, notable exceptions.

Adaptations to Heat

Humans dissipate excess heat through sweating/perspiration (evaporative cooling — though sweating too much can be dangerous) and vasodilation (widening of capillaries near the skin surface to increase blood flow and radiate heat).

Adaptations to Cold

Humans conserve heat through shivering (generating body heat through muscle contraction), vasoconstriction (narrowing capillaries at the skin surface), and behavioural adaptations (clothing, shelter, fire). Inuit populations have developed a long-term physiological adaptation involving cycling between vasodilation and vasoconstriction in the extremities.

Adaptation to High Altitude

At altitudes above 3,000 metres, hypoxia (oxygen starvation) becomes a significant challenge. Short-term adaptation includes increased production of red blood cells to carry more oxygen. Long-term adaptation includes increased lung capacity. Populations that have lived at high altitude for many generations (e.g., Andean and Tibetan highlanders) show genetically based physiological adaptations to low oxygen levels.

Clinal Variation in Skin Colour

Skin colour is one of the most visible and clinally distributed human traits. All humans have roughly the same number of melanocytes (melanin-producing cells), but they vary in the amount and type of melanin they produce.

Melanin absorbs UV radiation and protects against skin damage, DNA mutations, and folate destruction. In regions with intense solar radiation (near the equator), natural selection favours more melanin — hence the selective advantage of darker skin.

In northern regions, where UV radiation is weaker, the situation reverses. UV light stimulates vitamin D production in the skin, and vitamin D is essential for calcium absorption and bone health. Vitamin D deficiency leads to rickets (softening and deformation of bones). In low-UV environments, natural selection favours less melanin to allow more UV penetration for vitamin D synthesis — hence the selective advantage of lighter skin.

This elegant trade-off — between UV protection and vitamin D synthesis — explains the clinal distribution of skin colour across the globe.

Lecture 24: Race and Sex — Viewing Variation

Chapter 14 (continued)

Race and Ethnicity

Race is traditionally defined as a group of populations sharing certain biological traits that make them distinct from other populations. Ethnicity, by contrast, refers to perceived differences in culture, national origin, and historical experience.

Why Classification Matters

The concept of biological race has been used to justify social hierarchies, colonialism, and discrimination. Understanding why racial classification is scientifically problematic is therefore not merely academic — it has profound social and political consequences.

Problems with Biological Race

Biological anthropologists have identified at least five fundamental problems with the concept of biological race:

  1. No biologically distinct/discrete human populations exist. Human variation is continuous, not categorical.
  2. Continuous traits cannot be marked by discrete boundaries. Boundaries are arbitrary — when does “brownness” begin or end?
  3. Between-group variation is low. About 85–90% of all human genetic variation is found within any given population, not between populations.
  4. No suite of biological traits unambiguously identifies one’s race. For example, dark skin, tightly curled hair, and the sickle cell allele are all present in populations across Africa, the Middle East, and Asia.
  5. No one can agree on how many races there are, or their characteristics. Race is difficult to define, measure, and test scientifically.

Biological Determinism

Biological determinism associates physical characteristics with behaviour and abilities, arguing that some groups are naturally superior to others. This perspective has a long and ugly history, exemplified by figures such as J. Philippe Rushton (a controversial psychologist at the University of Western Ontario who proposed a racial hierarchy) and James Watson (co-discoverer of DNA’s structure, who made racially charged public statements about intelligence in 2007).

The anthropological consensus is clear: while human biological variation is real and important, it does not map onto racial categories in the way that biological determinism claims. Observed differences in health, educational achievement, and social outcomes between racial groups are overwhelmingly explained by environmental factors — poverty, lack of opportunities, unhealthy environments, institutional racism, and stress — not by inherent biological differences.

Race and Health

African Americans have approximately twice the rate of heart disease compared to Caucasian Americans. In 2005, the FDA approved BiDil, the first race-specific drug, aimed at treating heart failure in African Americans. Critics argued that this approach reflected biological determinism and racialization — the process of imbuing a person with consciousness of race distinctions. A more productive approach would examine how ideas about race become embodied through social processes, rather than assuming a biological basis.

Typological vs. Continuous Approaches

Two fundamentally different approaches to human variation exist:

The typological approach treats variation as discrete, simple, and focused on absolute difference — this is the approach underlying racial classification.

The continuous variation approach treats variation as existing on a continuum, recognizes its complexity, and focuses on gradations of similarity and difference. This is the approach favoured by modern biological anthropology, which asks: is our goal to create hierarchies, or to document and understand variation? Biological determinism, or a critical biocultural approach?

Sex, Gender, and Sexuality

Sex refers to the biological categories and characteristics of males and females. At its simplest, sex is determined by sex chromosomes: XX = female, XY = male, with the SRY gene on the Y chromosome triggering male development. However, non-sex chromosomes also carry genes integral to sex determination, making the picture more complex than anticipated.

Sexual dimorphism — the difference in form between males and females within a species — is present in humans but is relatively modest compared to many other primates (e.g., gorillas, where males are nearly twice the size of females).

Anne Fausto-Sterling’s provocative 1993 article “The Five Sexes” challenged the binary model by highlighting intersex conditions — congenital states characterized by atypical genitalia or discordance between genitals, sex chromosomes, and gonads. Intersex conditions occur in roughly 0.1–1% of the population. In her 2000 follow-up, “The Five Sexes, Revisited,” Fausto-Sterling shifted the discussion toward viewing sex as a spectrum rather than counting discrete types.

Modern biology increasingly recognizes that sex is determined not just by chromosomes but also by brains, genitalia, fetal hormones, pubertal hormones, and competing networks of gene activity within the body — as detailed in the 2015 Nature article “Sex Redefined.”

Lecture 25: Bioarchaeology I

Chapter 14 (pp. 331–337)

Bioarchaeology is the study of human skeletal remains from archaeological contexts to reconstruct past lifeways. By analyzing bones and teeth, bioarchaeologists can learn about violence, migration, disability, care, disease load, relatedness between groups, social stratification, activity patterns, ethnicity, migration, and mortuary behaviour.

Identifying Individuals

Skeletal analysis begins with the basics: How old was this individual at death? (assessed from dental development, epiphyseal fusion, and degenerative changes); What was their sex? (assessed from pelvic morphology and cranial features); How tall were they? (estimated from long bone lengths); and What was their ancestry? (assessed from cranial and dental morphology, though this is increasingly supplemented or replaced by DNA analysis).

Palaeodiet

Palaeodiet is the study of ancient diets using multiple lines of evidence:

Stable isotope ratios — particularly carbon-13 (13C) and nitrogen-15 (15N) — from bone collagen and tooth enamel reveal broad categories of foods consumed over time. Carbon isotopes distinguish between C3 plants (most trees and shrubs), C4 plants (tropical grasses, including maize), and marine resources. Nitrogen isotopes indicate trophic level — higher values indicate more animal protein in the diet.

Dental wear patterns reveal the types of foods consumed. Highly abrasive diets (e.g., grit-laden foods) produce heavy wear, while softer diets produce less wear.

Dental calculus (tarite) traps food particles, DNA, starches, and pollen, providing direct evidence of specific foods consumed.

Disease in the Past

Bioarchaeologists can identify many diseases from skeletal remains:

Infectious diseases leave characteristic marks on bone. Tuberculosis (Mycobacterium tuberculosis) causes abscesses at the ribs, hip, knee, and spine, potentially leading to ankylosis (fusion of joints). It is associated with population density. Syphilis (Treponema pallidum) produces characteristic “sunburst” lesions on the frontal bone.

Neoplasms (tumors) manifest in bone as either bone loss (lesions) or bone gain (tumors). Paleo-oncology — the study of cancer in antiquity — has revealed evidence of malignant osteosarcoma dating as far back as 1.8 mya in South Africa.

Origins and Migration

Isotope analysis can reveal where an individual grew up:

  • Oxygen isotopes (18O/16O) in tooth enamel reflect the water source during childhood — different regions have different oxygen isotope signatures
  • Strontium isotopes (87Sr/86Sr) reflect local geology — individuals who grew up in one geological region and moved to another can be identified by comparing the strontium in their teeth (formed in childhood) with the strontium in local soils

Lecture 26: Bioarchaeology II

Chapter 14 (pp. 337–345)

Reconstructing Past Lifeways

Beyond diet and disease, bioarchaeologists study many aspects of past life, including violence, migration, disability, care, disease load, relatedness between groups, social stratification, activity patterns, ethnicity, and mortuary behaviour and beliefs.

The Bioarchaeology of Body Modification

Human bodies have been intentionally modified in diverse ways throughout history and across cultures. Body modification raises questions of meaning — the body is central to communication, identity, and achieving social goals.

Reasons for body modification include:

  • Unintentional modification (e.g., habitual activities that alter bone)
  • Medical intervention
  • Mark of group identity (ethnic or class)
  • Mark of transition to adulthood
  • Beautification
  • Control or power over others

Cranial Modification

Cranial modification — the deliberate reshaping of the skull during infancy, when the cranial bones are still malleable — has been practiced across many cultures worldwide, including in the Democratic Republic of Congo, Europe, Peru, and among many Indigenous groups in the Americas. Modification was achieved through bindings, boards, or other devices applied to the infant’s head.

Motivations for cranial modification varied by culture:

  • Aesthetics/beautification: European, Polynesian, Maya, and North American groups
  • Ferocity: Huns and Andean groups
  • Intelligence — control and power: Maya (increase), Peruvian (decrease)
  • Ethnic identity: Russian, Andean, Polynesian, Australian, African, and North American groups
  • Social status: North American, African, Egyptian, European, Andean, and Maya groups

Dental Modification

Dental modification — filing, chipping, drilling, and inlaying teeth — has been practiced in many cultures. The Maya inlaid jade and other stones into their teeth. Vikings filed horizontal grooves into their front teeth. In Sumatra and elsewhere, teeth were filed to points.

Trephination

Trephination (trepanation) — drilling or cutting holes through the skull — is one of the oldest known surgical procedures, practiced across Old and New World cultures from prehistory through the 1990s. Possible purposes included cleaning up wounds, releasing blood buildup, and releasing spirits or “bad humors” (as a treatment for epilepsy or other conditions). Many trephined skulls show evidence of healing around the margins of the hole, indicating that patients survived the procedure.

Dr. Dolphin’s Research: Barqa Landscape Project

Dr. Alexis Dolphin’s own research includes work on the Barqa Landscape Project in Jordan, investigating paleopollution in Wadi Faynan — an area with extensive ancient copper smelting that may have affected the health of local populations. This research exemplifies the biocultural approach, examining how cultural activities (copper production) affected human biology (skeletal health markers).

These notes synthesize all 26 lectures of ANTH 204: Biological Anthropology, taught by Dr. Alexis Dolphin at the University of Waterloo, Winter 2021. The course textbook is Larsen’s Our Origins.

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