Biological Anthropology Flashcards

Biological Anthropology: Looking to the Deep Past

• Biological anthropology, also known as physical or evolutionary anthropology, is a major subfield of anthropology.
• It explores human origins and evolution by studying:
  • Human biological variation
  • Paleoanthropology (human and primate evolution)
  • Primatology (study of nonhuman primates)
  • Bioarchaeology (study of bones at archaeological sites)
  • Genetic anthropology (application of molecular science to reveal ancient origins and migration).

Exploring What It Means to Be Human

• Studies of human biological variation assess physical similarities and differences among human populations.
• Morphological differences include features like height, jawline, eye sockets, and ear/nose shape.
• Biochemical differences account for variations in the sense of smell, CCR5 gene mutations (HIV resistance), and skin pigmentation (response to UV rays).
• Figure 4.2 shows variations in skin pigmentation as evolutionary adaptations to different levels of UV exposure.
• The study of human biological variation is linked to the original conception of biological anthropology, formalized in 1930 with the American Association of Physical Anthropologists (now the American Association of Biological Anthropologists).
• The name change moves away from the term "physical anthropology" due to its association with scientific racism.
• In 1951, Sherwood Washburn introduced a “new physical anthropology,” shifting the focus to human evolution and the evolutionary process, expanding the field to include paleoanthropology and primatology.

Paleoanthropology

• Examines fossil evidence of human ancestors and ancient material culture (tools, artifacts).
• Analyzes skull and postcranial material (skeletal remains other than the skull) to form hypotheses about human evolution milestones.

Primatology

• Studies behavioral and physical attributes of living and fossil primates and their relationships with environments.
• Humans are primates sharing common ancestry with nonhuman primates.
• Studying nonhuman primates helps understand what it means to be a primate and what it means to be human.

Genetic Anthropology

• Combines DNA testing with archaeological, historical, and linguistic evidence.
• Reveals ancient human migration history and tracks human diseases.

Forensic Anthropology

• Applies scientific methods to analyze human remains for victim identification and cause of death determination.
• Focuses on crime scenes involving individual deaths, unlike other areas that focus on patterns in groups or populations.
• Played roles in identifying victims of war, disasters like the 2004 Thailand tsunami, and the destruction of the World Trade Center in 2001.
• Most forensic anthropologists work in medical examiner's offices, assisting with autopsies and skeletal examinations.

Bioarchaeology

• Studies human remains in archaeological settings.
• Focuses on what skeletal material reveals about culture, diet, and disease in a population.
• Interested in the socioecological system of a population, understanding the roles of environmental and ecological pressures.
• Explores social and funerary behavior, diet/nutrition, health, and disease based on biological remains.
• An example is skeletal evidence of infant cranial boarding, practiced by cultures like the ancient Maya and Inca, to deform the skull for aesthetic or social status reasons.
• Variations in how the board was attached to the skull provide information about an individual’s social identity.
• Figure 4.3 shows an elongated skull from the Nazca culture resulting from infant cranial bonding.

Profiles in Anthropology: Ann Rosalie David

• Born in Cardiff, UK, earned degrees in ancient history and a doctorate in ancient Egyptian temple rituals.
• Her work focuses on biological anthropology and Egyptology.
• Director of the KNH Centre for Biological and Forensic Studies in Egyptology at the University of Manchester.
• Established the Ancient Egyptian Mummy Tissue Bank.
• Served as keeper of Egyptology at the Manchester Museum.
• Collaborated with Egypt’s Ministry of Health and Population on public health projects, such as identifying antibodies against schistosomiasis in Egyptian mummies.
• Made an Officer of the Order of the British Empire (OBE) in 2003.
• Appeared in documentaries like Private Lives of the Pharaohs and Secrets of the Pharaohs.
• First woman in Britain to hold a professorship in Egyptology.
• Pioneer in biomedical research, studying disease, diet, and lifestyles in ancient Egypt.
• Her work on ancient Egyptian mummies suggests cancer may be partly attributable to modern pollution, diet, and lifestyle changes (David and Zimmerman 2010).
• Podcast discusses her work with ancient Egyptian mummies.
• Figure 4.4 shows Professor Ann Rosalie David.

Defining the Science of Taxonomy

• Taxonomy: the classification and naming of things, organizing them into groups based on criteria (e.g., color, height, traits, genes, behaviors).
• Critical in biological anthropology for organizing humans and evolutionary ancestors spatially and temporally.
• Taxon: Specific subgroup (e.g., genus).
• Taxa: Plural form of taxon, referring to all groups.
• The classification system for living organisms was developed by Carolus Linnaeus in the 18th century.

Binomial Nomenclature

• Linnaeus’s system, Systema Naturae, uses binomial nomenclature.
• Assigns two Latin names to each organism: genus name and species (trivial) name.
• Genus and species names are italicized; genus is capitalized, species is lowercase (e.g., Felis catus for house cat, Homo sapiens for humans).
• Established a universal scientific language across countries, avoiding confusion from regional names.
• Groups organisms sharing common traits (e.g., animals with mammary glands as mammals).
• Hierarchical classification scheme: organisms grouped into successive levels from domain to species.
• Linnaeus created five levels: kingdom, class, order, genus, and species.
• Humans: Kingdom Animalia, Class Mammalia, Order Primates, Genus Homo, Species sapiens.
• Additional levels added: domain, phylum, subclass, superorder, family, and tribe.
• These additions help better understand variations in different organism groups.
• Biological anthropologists primarily focus on understanding the species level.
• Figure 4.5 shows the Linnaean hierarchical classification for the monarch butterfly.

Defining a Species

• Species is difficult to define precisely.
• Basic level: a group of organisms with shared characteristics distinguishing them from other groups.
• Scientists distinguish species based on behavior, genetics, and/or morphology.
• Species definitions are the basis for scientific names.
• Common name of a species is based on general physical characteristics noted by a culture or local population.
• Common names are also referred to as folk taxonomy or ethnotaxonomy.
• There is growing interest in preserving Indigenous classifications and connecting them with scientific classifications.
• Classification decisions often involve taxonomic controversy, especially in biological anthropology.

Four Common Definitions of a Species

• There are a lot more than four definitions, but here's the four most common.
• Biological Species: a group of interbreeding organisms reproductively isolated from other groups.
  • Reproductive isolation: members cannot successfully mate outside their species.
  • Uses the ability to interbreed because successful mating leads to gene flow.
• Ecological Species: emphasizes natural selection's role in maintaining species boundaries.
  • Gene flow is neither necessary nor sufficient to maintain species boundaries.
  • Species boundaries are maintained even with substantial gene flow.
• Hybrid Zones: areas of overlap where two species successfully breed, and where gene flow occurs.
  • Example: Macaca maura (moor macaque) and Macaca tonkeana (Tonkean macaque) interbreeding on Sulawesi island for over 150 years.
• Phylogenetic Species: Determined by shared possession of one unique characteristic.
  • Identifying a trait unique to a group of fossil bones indicates a new species.
• Mate Recognition Species: a set of organisms that recognize one another as potential mates.
  • Example: American crickets producing distinct songs, with females mating only after hearing their species-specific song.
  • Analogous to the biological species definition where song acts as a reproductive isolating mechanism.

Issues with the Biological Species Definition

• Based on breeding behavior, making it problematic for identifying species over time.
• Hard to determine if fossil specimens were capable of interbreeding.
• Difficult to distinguish between interspecific variation (differences between two different species) and intraspecific variation (variation within a species) in the fossil record.

The Units of Life

• Cells are the basic units of life in all organisms and are capable of self-reproduction.
• There are two main types of cells: prokaryotic and eukaryotic.
• Prokaryotes: single-celled organisms like bacteria and archaea.
• Eukaryotes: more complex, multicellular organisms (plants, animals, humans), contain a nucleus.
• The nucleus houses the genetic material, or DNA (deoxyribonucleic acid), that controls cellular function.
• Two types of eukaryotic cells: somatic cells (structural components) and sex cells (gametes) involved in reproduction.
• Sex cells unite to form a fertilized egg (zygote).
• In animals, there are two types of sex cells: ova (eggs) and sperm.
• Cell division produces new cells: mitosis (somatic cells) and meiosis (sex cells).
• Mitosis: parent cell divides once to produce two identical daughter cells; DNA forms chromosomes (each daughter cell inherits 46 chromosomes).
• Figure 4.6 illustrates somatic cell division (mitosis).
• Meiosis: two cellular divisions in testes/ovaries result in four daughter cells.
• Each daughter cell receives half of the parental genetic material (23 chromosomes).
• Genes are housed on chromosomes, and are the fundamental unit of heredity.
• Genes are the sequence of DNA material in the nucleus.
• Genotype: The genetic material within an organism’s cells.
• Phenotype: Observable traits expressed by genes.
• Allele: A variation of a gene that activates a specific trait.

Gregor Mendel and the Laws of Heredity

• The true nature of inheritance was not understood until the rediscovery of Gregor Mendel’s work in the 20th century.
• Cell theory influenced Mendel, raising questions about parental contributions to offspring cells.
• In 1854, Mendel began experiments with pea plants.
• Figure 4.7 depicts Gregor Mendel.
• First stage: identifying plants that breed true (each parent only produces one kind of offspring when self-crossed).
• Self-cross: self-mating in plants with both male and female parts.
• Purebreds (P1 generation): plants that always bred true.
• Mendel selected seven traits of pea plants with two distinct phenotypes (observable expressions of the trait).
• Studied mating and traits of over 28,000 plants over eight years.
• First round of experiments: monohybrid cross (mating between two purebred individuals differing in a single characteristic).
• Parent pea plants differed in pod color or seed shape.
• Figure 4.8 shows distinct characteristics observable in pea plants.
• Mendel mated a purebred yellow pea plant with a purebred green pea plant.
• All offspring were yellow (hybrid plant, parents differ in a specific characteristic).
• Dominant: expressed trait (yellow).
• Recessive: disappeared trait (green).
• Mating two hybrid plants resulted in recessive traits reappearing in a ratio of three dominant to one recessive.

Mendel’s Laws of Inheritance

• Mendel noted that trait expressions were controlled by discrete units occurring in pairs, with offspring inheriting one unit from each parent.
• Mendel’s first law of inheritance is the law of segregation: two alleles for each trait segregate during gamete formation and combine randomly during reproduction.
• The process of meiosis explains Mendel’s law of segregation.
• Each trait is controlled by a pair of genes, one on each chromosome.
• Chromosomes separate during the reproductive cycle, so each gamete has only one allele for each trait.
• Figure 4.9 shows Punnett squares, a method for predicting breeding experiment results.
• Dihybrid cross: A cross between individuals who differ with respect to two gene pairs.
• After establishing his first law of inheritance, Mendel extended his studies to more complex situations, using dihybrid crosses.
• Example: cross between a plant with round yellow peas and a plant with wrinkled green peas.
• In the second generation, Mendel found that 9/16 of the offspring were round and yellow, 3/16 were wrinkled and yellow, 3/16 were round and green, and 1/16 were wrinkled and green.
• The results of these dihybrid crosses indicate that the two characteristics—pea color and pea shape—segregate independently.
• The expression of one trait is not influenced by the expression of the other trait.
• Law of independent assortment: alleles coding for different traits sort independently during meiosis--division of sex cells.

Mendelian Inheritance in Humans

• Evolutionary perspective: contemporary biological anthropologists utilize an evolutionary perspective.
• Contemporary biological anthropologists utilize an evolutionary perspective: the principles of evolution are used to understand how and why living organisms, including people, thrive in almost every environment on Earth.
• Natural selection is accepted as the guiding force that shapes why living things are the way they are.
• This chapter relies on the foundational assumption that natural forces are the only forces directing the development of life on Earth.
• Natural selection: out of all the possible variations of beings competing for the same resources on Earth, those that prospered were the ones better suited to their environments than all other competitors.
• Mendel’s laws of inheritance apply to humans, accounting for the transmission of human traits.

Examples of Inherited Human Traits

• Blood type (A, B, O) based on three alleles of a single gene. O is recessive to both A and B, while A and B are codominant.
• Codominance: products of both alleles are observed instead of one masking the other.
• Mendelian traits (controlled by a single gene) include Huntington’s disease, widow’s peak, cystic fibrosis, sickle cell anemia, Tay-Sachs disease, hemophilia, and red-green color blindness.
• OMIM (Online Mendelian Inheritance in Man): an online database of almost 5,000 Mendelian human traits.
• The majority of human traits are not controlled by a single pair of genes.
• Polygenic traits: multiple genes needed to produce a single effect.
• Determining if a trait is polygenic is to assess whether the trait can be measured, such as height or weight.
• Traits that can be measured, that have a wide range or lots of variability and can be affected by environmental factors are probably polygenic.
• Survival of a species depends on genetic diversity and variation.
• Reduction of a gene pool due to geographic isolation or other environmental factors puts a species at risk of extinction.

Early Evolutionists and the Fixity of Species

• Evolution: change in allele frequency within a gene pool that can lead to changes in an organism’s morphology (form and structure) over time.
• Evolution involves the processes of mutation, natural selection, and speciation
• Prior to the 19th century, the prevailing idea in Western thought was that nature was fixed and static.
• The great chain of being: living creatures were arranged within a set order decreed by God: God, angels, humans, animals, plants, and minerals.
• From the 14th-18th centuries, some began to question the static view of nature.
• Robert Hooke: first person to claim not only that nature has changed over time but also that evidence of these changes remain.
• Fossils are the remains of actual plants and animals that were once alive.
• Earth's geography and physical features experienced dramatic changes.

Jean-Baptiste Lamarck

• Proposed first theory of macroevolution.
• His theory relied on the now defunct idea of the inheritance of acquired characteristics.
• Lamarck argued that organs and traits that help a creature to survive will become bigger and more complex over time, while those that are of little use will become smaller and simpler and eventually disappear.
• Classic example: the long neck of a giraffe; giraffes would stretch their necks to reach the leaves at the tops of trees, their necks would grow longer, and furthermore, these longer necks would be inherited by the subsequent generations. This theory of the inheritance of acquired characteristics is also known as Lamarckian inheritance.
• Lamarck’s theory is that wishes, desires, wills, and needs were all sufficient to motivate change.

Primary Issues with Lamarckian Inheritance

• Desires, wishes, and needs do not change physical characteristics without a deliberate change in behavior.
• The inheritance of acquired traits is not possible.
• Traits acquired during a lifespan are not passed on to subsequent generations.
• Lamarck recognized the importance of interactions between organisms and their environments in the evolutionary process and was the first to propose a mechanism by which evolutionary change from one species into another could actually occur.

Georges Cuvier and Other Contributors

• French scientist Georges Cuvier contributed to evolutionary thinking, best known for his theory of catastrophism.
• Catastrophism: floods, earthquakes, and other natural disasters—understood within the theory as acts of God—have been responsible for killing all the animals alive in certain places at certain times. Either new animals have been created or the areas had been repopulated by animals from neighboring areas.
• Cuvier proposed that new organisms with a more modern appearance were the result of a more recent creation event.
• Cuvier’s idea of extinction continues to be an important component of evolutionary thinking today.
• Scottish geologist Charles Lyell, known as the father of modern geology, argued that contemporary geological processes were the same as those that occurred in the past; this is known as the principle of uniformitarianism.

Charles Darwin’s Role in Changing Views of the Natural World

• Darwin introduced a new way of seeing the world that was both highly criticized and acclaimed in the scientific community of his time.
• His theories of natural selection became the foundation of biological science.
• New knowledge pertaining to genetics and molecular science has strengthened Darwin’s theories rather than weakened them.
• Darwin studied to be a medical doctor at the University of Edinburgh but decided to instead learn taxidermy under John Edmonstone; figure 4.10 shows Embernagra platensis, the great Pampa-finch, collected by Charles Darwin in Uruguay in May of 1833.
• John Edmonstone was born enslaved in what is now Guyana in South America and would visit the plantation often.
• Charles Waterton, the son-in-law of the plantation owner and a renowned naturalist, would invite Edmonstone to accompany him on his frequent travels into the rainforest.
• On his travels, Edmonstone gained considerable knowledge about the flora and fauna of South America along with impressive taxidermy skills.
• After gaining his freedom in 1817, John Edmonstone taught taxidermy at the University of Edinburgh, where he served as a mentor to Darwin over a period of several months.
• Darwin’s relationship with Edmonstone may have influenced his abolitionist views, which were later strengthened by firsthand accounts of slavery while Darwin was on his infamous voyage to the Galápagos Islands off the coast of Ecuador.
• Figure 4.10 shows Darwin learning to preserve birds from Edmonstone.

Darwin the Explorer and Scholar

• Darwin decided to pursue theology at Christ’s College, Cambridge.
• Darwin was appointed as a naturalist on the HMS Beagle for a five-year scientific expedition around the world.
• Darwin collected, dissected, and organized various specimens, especially in the Galápagos Islands.
• His observations in the Galápagos marked a crucial point in his thinking on evolution.
• He noted that the fauna and flora of the western coast of South America were similar to those he observed in the Galápagos but distinct enough to be considered different species.

Natural Selection: Darwin's Theory

• Darwin observed 13 different types of finches throughout 13 different small islands--each species was specifically adapted to the specific habitats on each of the islands.
• Darwin used the techniques that Edmonstone taught him to preserve the Galápagos finches, which became key pieces of evidence supporting Darwin’s theory of natural selection.
• Darwin had been thinking about artificial selection—the selective breeding of animals to produce traits that humans find useful.
• Darwin read a book by English economist Thomas Robert Malthus titled An Essay on the Principle of Population (1798).
• Darwin obtained two important points from this book:
  • Human populations, if unrestrained, will grow exponentially--they will double each generation.
  • Food resources increase much more slowly than population does.
  • Malthus noted that the growth of human populations is kept in check by a limit of food resources, which creates a struggle for existence.

The Struggle for Existence

• The struggle for existence is about an individual’s ability to both find enough food and not become another organism’s food.
• Individuals with favorable characteristics for living in an environment are the ones that will survive to the age at which they reproduce, while those with less favorable variations will not.
• This mechanism for “selecting for” certain traits and features is known as the theory of natural selection.
• Darwin concluded from his observations that when a group of animals of the same species are geologically separated, they develop into separate species.
• This evolutionary process is commonly referred to as allopatric speciation (or geographic speciation) and is based on the principles that related species share a common ancestor and that species change over time.

Darwin and Wallace

• Darwin did not originate the idea of evolution.
• Many of the ideas used by Darwin in his theory of natural selection were developed by other thinkers.
• Darwin was also not the only person thinking about natural selection.
• Alfred Russel Wallace, developed the same idea at roughly the same time, entirely independently of Darwin.
• Wallace’s thinking was influenced by his own travels through the Malay Archipelago between Indochina and Australia.
• Wallace outlined his theory of evolution by natural selection in a letter written to Darwin while he was in Malaysia.
• Darwin finally published his book On the Origin of Species, some 20 years after his voyage on the HMS Beagle.
• Figure 4.11 shows Charles Darwin.

Understanding Darwin’s Theory of Natural Selection

• All organisms are capable of producing offspring faster than the food supply increases
• All organisms show variation
• There is a fierce struggle for existence, and those with the most suitable variations are most likely to survive and reproduce.
• Variations, or traits, are passed on to offspring (inherited).
• Small changes in every generation lead to major changes over long periods of time.
• Survival of the fittest: refers to those who are most evolutionarily fit (not necessarily the biggest or fastest.)
• Herbert Spencer, who promoted the now discredited ideology of social Darwinism, first used this term.

Social Darwinism

• Social Darwinism applied the concept of Darwin’s biological evolution to human societies, proposing that human culture was progressing toward the “perfect human."
• Spencer’s writings became integrally related to the 19th-century rise of scientific racism and European colonialism.
• Figure 4.12 shows a peppered moth camouflaged on a tree trunk.
• Examples of Darwin’s theory of natural selection can be found throughout the natural world.
• One example is the color change observed in peppered moths in England during the 19th century.
• Before the Industrial Revolution, peppered moths in England were a light grey color, well camouflaged on tree branches and less likely to be eaten by birds.
• When soot from coal factories began to cover the bark of the trees, the black moths became better camouflaged and the white moths were now more visible.
• Consequently, the black moths were the ones to survive to reproduce, while the white ones were eaten -- termed industrial melanism.
• As coal usage decreased and the bark of the trees once again became lighter in color, white moths again dominated the urban areas

Examples of Natural Selection in Modern Times

• Pesticide resistance in insects: This refers to the decreasing susceptibility of a pest population to a pesticide that previously was effective at controlling it.
• The rise of "superbugs: These are bacteria that have become increasingly resistant to antibiotics.

The Processes of Evolution

• Mutation is the creative force of evolution and represents the first stage of the evolutionary process.
• Mutation is defined as an alteration in a genetic sequence that results in a variant form.
• For a mutation to have evolutionary significance, it must occur in the sex cells (sperm and ova).
• Mutations in non-sex chromosomes will not be passed on from one generation to the next.

The Nature of Mutations

• Other evolutionary forces can modify existing genetic material, only mutation can produce new genetic material.
• One of the most interesting things about mutations is the fact that they are random.
• There is no way of predicting when a specific mutation will occur; all scientists can do is estimate the probability of a mutation occurring.
• Mutations do not necessarily appear when they are needed.
• Advantageous mutations lead to changes that improve an individual’s survival and/or chances of reproduction.
• Neutral mutations have no effect on survival or reproduction.
• And some mutations are in fact quite harmful and do negatively affect certain individuals’ survival and reproduction.
• Mutations generally occur spontaneously in response to conditions in the body or in the environment.
• The probability of a mutation at any given gene is between 1 in 10,000 and 1 in 100,000.
• Figure 4.13 shows genetically modified mosquitoes.

Genetic Drift

• Genetic drift is defined as the effect of random chance on a population, notably the way in which it determines whether an individual survives and reproduces or dies.
• Genetic drift—random chance—was affecting the composition of the candy in your Halloween bucket.
• Genetic drift is directly and inversely related to population size.
• The smaller the population, the larger the influence of genetic drift; the larger the population, the smaller the influence of genetic drift.
• In a large population, say 100,000, removing a couple of individuals will have a truly miniscule effect on the population.

Gene Flow

• Gene flow is another important evolutionary force, involving the exchange of genetic material between populations and geographic regions.
• Without gene flow, there would be no diversity—and without diversity, a species is at higher risk of extinction.
• Figure 4.14 shows how pollination is a good example of gene flow.
• Anytime a gene is introduced to a new population where it did not exist before, that is gene flow.

Speciation

• Speciation is the rise of a new species in response to an environmental change or pressure.
• Allopatric speciation is created by geographic barriers such as mountains, rivers, or oceans; figure 4.15 shows the different species of squirrel found on the two sides of the Grand Canyon.
• Sympatric speciation involves species that are descended from a common ancestor and remain in one location without a geographic barrier; is seen in the East African cichlid fish, which experience reproduction isolation due not to a physical barrier but to females’ selection of mates with certain coloration.

Adaptive Radiation

• Adaptive radiation is when one or more species give rise to many new species in a relatively short time.
• An explosion of about 250 very diverse species of cichlids in Lake Tanganyika occurred in less than 10 million years (Takahashi and Koblmüller 2011).
• Other research suggests that the common ancestor was the result of a hybrid swarm from two different locations (Meier et al. 2017).
• Figure 4.16 shows how there are more than 250 different species of East African cichlid fish, all traceable to two common ancestors.
• In peripatric speciation, members of the same population are separated and over time evolve as separate species.
• Ring speciation occurs when several species coexist for a time in a region near one end of a geographic barrier.
• Reproductive isolation is strongest for that part of the population that is farthest away from the original population.
• Examples like the different species of the California salamander genus Ensatina is believed to have developed through the process of ring speciation; figure 4.17 shows the different species of the California salamander genus Ensatina.

Gradualism vs. Punctuated Evolution

• Gradualism refers to evolutionary changes occurring gradually and accumulating in a single unbroken and unbranching line
• What can be observed in the fossil record are static populations that are interrupted by sudden bursts of change--punctuated equilibrium.
• What can be observed in the fossil record are static populations that are interrupted by sudden bursts of change.
• This phenomenon of long periods of stasis, or no change, followed by quick periods of change is known as punctuated equilibrium.

The Tree of Life

• Evolution is neither linear nor progressive, but rather a branching process—a tree of life containing both areas of divergence and points of a shared common ancestry.
• During Darwin’s time, evolutionary relationships had to be determined largely by structural morphologies and physical characteristics
• Figure 4.18 shows Darwin's sketch of evolutionary relationships.
• Binomial nomenclature provides clues to evolutionary relationships; figure 4.19 shows monarch and viceroy butterflies
• Linnaean classification has limits
• Species exhibiting mimicry and larval forms can take on appearance of other organisms
• Close examination reveals that the markings on the wings are a bit different.
• The monarch is on the left, and the monarch mimic, the viceroy, is on the right

Structural Morphologies and Examples of Evolutionary Relationships

• Structural similarities may be derived traits (homologous structures), inherited from a common ancestor, or they may have developed independently (analogous structures).
• Homologous structures: grasping hand found in both humans and chimpanzees, which suggests that humans and chimpanzees share a common ancestor that also had a grasping hand
• Analogous structures: the wing of a butterfly and the wing of a bat--likely developed independently and do not necessarily share a common ancestor
• Identifying homologies is essential for creating hierarchies of phylogenetic relationships because homology indicates that shared features are due to common descent.
• Cladistics, or the use of cladograms, is a method of visually distinguishing between homologous ancestral and derived characteristics.
• Ancestral characteristics are found in the common ancestor of the species being classified, whereas derived characteristics are only found in the groups in question.
• An ancestral characteristic that humans share with common ancestors is opposable thumbs; a derived trait that is only found in modern humans is the chin.
• The structural similarities are homologous, meaning that the similarities are the result of these animals sharing a common ancestor; figure 4.21 refers

Molecular Biology & The Tree Of Life

• Molecular science has provided additional tools and lines of evidence to verify evolutionary relationships.
• Phylogenetic tree: a model used by modern taxonomists to reveal the complexity and diversity of life and its many branches; figure 4.22 represents the phylogenetic tree.
• Phylogenetic trees show how species and other taxon groups evolved from a series of common ancestors.
• They are based on both physical and genetic evidence.

What Is a Primate?

• Primates—including human beings—are characterized by a number of distinct physical features that distinguish them from other mammals:
• ● opposable thumbs and (in nonhuman primates) opposable big toes;
• ● the presence of five digits (fingers or toes) on the appendages;
• ● flat nails instead of curved claws;
• ● pads at the tips of the fingers made up of deposits of fat and nerves;
• ● reduced reliance on sense of smell and a relatively small snout;
• ● depth perception;
• ● binocular vision (being able to see one image with both eyes);
• ● a relatively slow reproductive rate;
• ● relatively large brain size; and
• ● postorbital bars (bony rings that completely surround the eyes).
• Figure 4.23 shows orangutans, one of many living primate species.

Primates Compared to Other Mammals

• The first four traits enhance dexterity and enable primates to use their hands and feet differently from other mammals.
• Other traits on this list represent a shift in emphasis among the sense organs between primates and other mammals.
• Primates are characterized by a greater emphasis on vision and a reduced reliance on smell relative to other mammals.
• The hands of a bonobo, including its opposable thumbs, look very similar to human hands in figure 4.24

Primate Behavioral Variation

• Comparative studies of humans with nonhuman primates help answer this question:
• “What makes us human?”
• Comparing the behavior of nonhuman primates and the behavior of human beings helps anthropologists identify what culture is and develop operational definitions for it.
• Without the comparative perspective provided by primatology, anthropologists would be missing an important piece of the puzzle of what makes humans human--would not be able to fully understand humankind.
• Studying nonhuman primates in their environment is key to understanding variations in behavior and can shed light on humanity’s ancient past.

Primate Habitats

• Primatologists are studying the chimpanzees at Gombe National Park in Tanzania, where they live in the rainforest.
• The behavior of chimpanzees that live in the tropical regions of Africa is quite different from the behavior of chimpanzees that live in the savanna at Fongoli in Senegal, in West Africa.
• Gombe chimps hunt red colobus monkeys without the use of tools while the Fongoli chimpanzees hunt galagos (also known as bush babies) using sticks that they adapt and used as spears (Pruetz, J.D, et al, 2015)
• An important question that primatologists and biological anthropologists seek to answer is the question, do nonhuman primates have culture?

Primate Culture

• Whenever we see an exchange of ideas where one individual is involved in teaching another and when that knowledge is passed on to others in a group is according to anthropologists, a form of culture.
• Figure 4.25 shows a chimpanzee from the Gombe National Park in Tanzania.
• We see this happen in chimpanzee groups where older chimpanzees teach the young how to use sticks to termite-fish, the process of extracting termites from a termite mound using a stick.

Explaining Primate Success

• Why primates evolved as they did and how they filled and exploited the range of ecological niches they now fill are questions that have not yet been adequately addressed.
• Over the last century, various hypotheses have been raised to account for the evolution of primates and their unusual anatomical characteristics. These theories include the arboreal theory, the visual predation hypothesis, and the angiosperm theory.

Hypotheses for Primate Evolution

• Arboreal theory: primates evolved traits as an adaptation to life in the trees; Matt Cartmill complicated this theory, recognizing that forward-facing eyes are characteristic not only of primates but also of predators such as cats and owls that prey on small animals.