Anthropology 201

Biological Anthropology

Subfield of anthropology that studies humans as a biological species

• we are subject to the same processes that shape all living species

Trying to understand how humans came to be as we are today.

Theory of Evolution

Change through time - the framework that allows us to understand how species came to be today.

A Theory that is constantly tested, and never falsified, supported by genetic evidence, and has stood the test of time

Evolution

Changes in gene frequencies in populations between generations

A change in the inherited characteristics of biological populations over successive generations - a change in phenotypes reflects changes in the underlying genetic composition of the population

• including the appearance of new species

• changes occur at all levels of organization, species, individuals, and molecules

Microevolution

Evolution within populations -species

changes in allele frequencies and associated traits within populations

Macroevolution

Changes that occur after many generations. Speciation, claves, etc.

Evolution of species, genera, families, and other higher order levels of classification

relevant to interpret the fossil record

Stasis of species

Fixity of species(Christian) - all life forms were created by god, and therefore are perfect, without need for change

Great Chain of being (aristotle) - all life forms belong within a hierarchy based on complexity. Humans near the top, below a deity

Previous thoughts on Earths age

Based on Christian scripture, earth was believed to have began Sunday October 23rd, 4004 B.C. Making the earth only ~6000 years old today

Scientific Revolution

A shift in understanding of our world and its inhabitants

Development of the scientific method, creating room for experimentation, theories/hypothesis

Discovery of the new world forced a change in fundamental views about our world.

• Exposed us to new plants/animals

Carolus Linnaeus - Systema Naturae

Father of taxonomy - created the binomial nomenclature (genus species). Took collections of speices and organized based on similarities/differences in morphology.

Placed humans among animals, with primates - which he named 42 of. (likely multiple races called different species)

Erasmus Darwin

Charles Darwins grandfather

proposed that species may have evolved from a common ancester (Zoonomia)

Georges Cuvier

First real paleontologist, established it as a discipline.

Proved that species had and therefore could go extinct using fossil evidence. This went against christian doctrine.

began the study of the earths fossil record

Jean-Baptiste Lamark

Advocate for evolution of species:

• Idea that as environments changed, animals changed through use/disuse of structures. As they adapt through their lives, the aquired changes are passed down to offspring.

The idea of inheritance of acquired characteristics

Thomas Malthus

Political economist/demographer - Essay on the Principle of Population

• Populations grow exponentially when they can, until checked by famines, disease, etc. Populations grow exponentially while resources only grow linearly.

• Competition to survive - plants and animals produce more offspring than can survive. Mutations that are beneficial for survival are more likely to be passed on.

Social ills caused by

• Overproduction of children + moral irresponsibility of people

Charles Lyell

Uniformitarianism - the same processes occuring on earth today (erosion, landslides) Influnced the earth in the past.

• The earth must be much older than current views allowed.

Alfred Russel Wallace

Fellow ship naturalist who indepentantly developed the idea of natural selection. Reached out to Darwin to compare notes, leading them both to publish.

They proved each other, but Darwin was a better communicator.

Darwins Influences - Summery

Lyell: The earth is old enough for significant changes to have taken place

Lamarck: Species can change over time

Malthus: Organisms compete over limited resources

his identity and background

General reading and correspondence

his experience as a naturalist

Darwins Contribution

Provided a mechanism for organic evolution: Adaptation by natural selection

• Species can change

• Species evolve from other species through the mechanism of natural selection

Darwins 3 Postulates

1. Individuals compete because resources are finite

2. Individuals vary in ways that affect their ability to survive

3. Some variation must be heritable

Darwins First Postulate - Competition

Populations can expand indefinitely, but resources are always finite

Individuals compete for limited resources within a particular habitat

Not all individuals survive long enough to reproduce

Darwins Second Postulate - Variation

There is variation among individuals in a population

Some individuals will possess traits that make them more successful (higher fitness)

Those traits allow them to survive and reproduce or produce more offspring

Darwins thrid Postulate - Heritable

Differences amoung individuals are transferred from parents to offspring

Those advantagous wil become more common in successive generations

He did not understand the mechanisms of inheritance

Natural Selection

The process that leads to adaptations when the three postulates hold

Acts on variation

can provide directional change in allele frequency (relative to environment)

If the environment changes, selection pressures change. If the environment changes long-term in the same direction, the allele frequencies will shift gradually from generation to generation

Adaptation

A trait that is shaped by natural selection and allows the individual to survive and reproduce more successfully (increases fitness)

Arrtificial selection

Naming it natural selection, Darwin explains that if us humans are manipulating other genetics, surely nature can as well.

Directional selection

One of the extremes is selected against, leading to a shift towards the opposite extreme

Stablizing selection

Both extremes are selected against. The mean remains constant, but variation decreases. Preserves the status quo

Disruptive Selection

The median/mean is selected against, leading to two extremes, eventually leads to speciation

Misconseption - natural selection can’t explain the evolution of complex traits

while some changes occur quickly, many smaller changes over a long period of time can lead to massive changes.

tinkering not building

Convergent evolution - many animals have evolved to appear very similar even though they have no near ancestors

Misconseption - Units of selection

Natural selection occurs at the individual level, not the species/group

Evolution occurs at the population level

• changtes in gene frequencies

Misconseption - All traits are adaptive

Traits are only adaptations if they contributes to fitness. Some current traits are results of former adaptations, and some traits are just traits

Misconseption - Evolution is progress

Evolution does not always progess in one direction, meaning there is no such thing as better - only better suited to a certain environment

Why weren’t his ideas accepted?

Went against religous views, as it is a result of natural processes, not a higher power.

He couldn’t properly explain two of the three postulates.

• wasn’t sure how variation could be maintained (blended inheritance)

• Couldn’t explain the mechanism of inheritance

19th Century View of inheritance

Offspring appeared to be an average of the traits of their parents, attributed to blended inheritance, which should have led to a decrease in variation over time.

The Cell

Basic units of life

Complex life forms are made up of billions of cells.

• Adult humans = ~1 trillion cells

Comrpomised of genetic material and other structures

Prokaryotic Cells

Life originated on earth as these cells 3.7 billion years ago

Single celled organisms

• bacteria

• algae

Notable have no nucleus around the genetic material in the cell

Eukaryotic Cells

Structurally complex cells

appeared 1.2-2.1 billion years ago, sharing a common ancestor with prokaryotc cells

Genetic material is contained within a nucleus

all other things on earth other than bacteria/algea

Chromosomes

Small linear bodies contained in the cell nucleus

replicated during cell division

exist in homologous pairs in diploid organisms

• humans have 23 pairs

• two copies of each chromosome (one from each parent)

Mitosis

Normal cell division

creates two exact copies of chromosome pairs (diploid)

Part of normal growth in the body

Meiosis

Special cell division just to produce gamates

creates single chromosomes (half of a pair) in a haploid gamete

Meiosis and Fertilization

Haploid sperm joins a haploid ovum, forming a new pair of chromosomes in a diploid zygote

Zygote then divides through mitosis to build a new organism

State of affairs by 1950

Cell division mechanisms are well known

Chromosomes contain two complex molecules

• proteins (histones)

• Nucleic acids

DNA likely carries hereditary information

DNA Structure

Discovered by Francis Crick and James Watson 1953

Matching strands in a double helix, 2m long chromosome

backbone of phosphate and sugar

Inner links between strands are pairs of nucleotides - bases

• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Thymine (T)

A only bonds with T, C only bonds with G

1 cell has ~3 billion base pairs

DNA is excellent for storage of information

Stable molecule → information is safely stored

Cellular machinery can read the information and replicated it to extreme accurace (1 mistake per 1 billion BPs)

DNA encoding

1. some codes for proteins (specify the sequence of amino acids)

2. Some codes for regulatory sequences

Leading to variation of traits

Protein-coding genes - enzymes

Catalyze chemical reactions in cells, going from one compound to another involved the structure and function of those cells

DNA encoding non-enzymatic proteins

Other DNA sequences encode proteins that are not involved in enzymatic reactions but play a role in the normal structure and function of cells

DNA specifies the primary structure of proteins

DNA is paired in codons, the sequence of which codes for amino acids that are folded into complex 3D shapes

64 codens are possible, only 20 amino acides are present. multiple code for the same amino acids

redundance in coding protects against deleterious changes in protein structure caused by DNA damage (synonymous substitutions)

Exons and Introns

In eukaryotes genes contain coding sequences interrupted by one or more non-coding sequences

• introns are removed then the exons are spliced back together

important source of protein diversity + variation

same DNA sequences can code for multiple proteins

• >80% of human genes are alternatively spliced

Some DNA encodes regulatory sequences

Operators that determine if/when other protein-coding sequences are expressed

Non-coding but near the protein coding sequence

Usually binding sites for repressor or activator proteins

large source of phenotypic variation

Regulatory Sequences

All cells have the complete genetic library

if all DNA was expressed, then all cells would be the same

gene regulation for cell differentiation from single cell zygote

varitation arises due to differential regulation of the same DNA among cells

Changes to DNA - mutation

Mutations can occur as copying error in transcription during DNA replication - point mutations

Other types of mutations can cause a change in chromosome #/structure

Mutations are not always negative - source of variation

Mutation

Change in DNA sequence

Changes to DNA - recombination

New combinations of alleles through breaking and rejoining of DNA strands into a new order

can occur during meiosis when chromosomes are paired

• maternal/paternal chromosomes exchanging a piece of DNA - crossing over

• can occur during transcription.

Gregor Mendel

Silesian Monk who completed a series of experiments on garden peas, leading him to establish mechanisms of inheritance

Mendels Experiments

Used true-breading peas (yellow/green, wrinkled/smooth)

• cross-bred variants for several generations

• Discrete types - no blending of traits

Led to key concepts in inheritance

particulate inheritance

• traits determined by discrete “particles” passed intact from parents to offspring (genes)

Dominant and recessive traits

two laws

Dominance

A variant of a ‘particle’ (gene) that suppresses other forms

F0 - true breeding peas, homozygous for their specific colour

• yellow gamates were all A, green all a

F1 cross btw true breeding yellow/green were all Aa, and presented yellow.

Yellow allele was dominant

Recessive

A variant whose expression is suppressed by dominant forms

Law of Segregation

• alternative versions of genes account for varitation in inherited characters

• For each character, an organism inherits two genes (1 from each parent) and only passes 1 one (haploid gametes created through meiosis)

Law of Independent Assortment

• Each particle equally likely to be transmitted when gametes (eggs/sperm) are formed

• Emergence of one trait will not affect the likelihood of emergence of another trait

  • Yellow vs Green will not impact wrinkled vs smooth

Rediscovering Mendel

While his work was published in 1866, his insights were ignored for ~40 years. Rediscovery in 1900 was promted by advances in cell biology

• cell theory (all living beings made of cells)

• cell anatomy - chromosomes

• Cell division - mitosis/meiosis

Genes

Segment of DNA that makes a functional product and segregates as a unit during gamete formation

Unit of heredity

A segment of DNA that makes a functional product and segregates as a unit during gamete formation

Composed of introns and exons

Arranged on chromosomes like beads on a string

each gene is found at a specific point on the chromosome

Have alleles - multiple variants of a gene

Alleles

Variation of a gene

Homozygous

An individual who carries two identical alleles for a given gene

Heterozygous

A person who carries two different alleles for a gene

Genotype

The combination of alleles an organism carries

Phenotype

Observable characteristics of an individual

Two traits - linkage

Independant assortment for traits is predictable when traits are found of different chromosomes, but when located on the same chromosome, their transmission is connected

Crossing over

Allows for variation in linked traits, where homologous chromosomes can break and recombine during meiosis, created new combinations that did not exist in the parents.

• impacted by loci. Two traits close together on a chromosome are less likely to recombine than ones on opposite ends

Genotypes/phenotypes - A blueprint

BB and Bb often create the same phenotypes, and many phenotypes depend on the environment, as the same genotype can look very different depending on the situations surrounding them

• height gene without nutrients needed to grow = short

Population genetics

The study of changes in gene frequencies in populations under natural selection

The Modern Synthesis

The synthesis of genetics and Darwinian evolutionary theory.

reconcilled genetic processes with gradual evolution by natural selection, accounts for generation and maintenance of continuous variation

Traits can be controlled by many genes, each of which only has a small impact on phenotypes

Continuous Variation

Where traits present as a range of phenotypes, not a set pair/handful of options (height) . Caused by multiple genes controlling the single trait, and environmental impact, creating a bell curve of options

Environment Variation

Phenotypes are often affected by the development and environment avaliable (food resources, parental guidence, prenatal nutrition, etc)

Allows for a smooth overlap in phenotypes that arise from discrete genotypes

Blending phenotypes without blending genotypes

Forces of Evolution

Natural Selection (reduces variation)

Mutation (increases varitation)

Gene Flow (maintains variation)

Genetic drift (typically decreases)

Forces of Evolution - Natural selection

Reduces varitation by removing disadvantageous phenotypes (and their underlying genotypes)

Forces of Evolution - Mutation

Increases varitation through the creation of new variants

Gene Flow

Maintains variation and can introduce new variants into a population (by moving them around, not creating new ones)

The movement of genetic material within or between populations

• maintain similarities between members of the population(s)

• counters the effect of selection for different phenotypes

Evolutionary constraints

A factor limiting the adaptative potential of phenotype

• limits direction, nature, rate, and amount of evolutionary change that is possible

• can prevent evolution of optimal adaptations, and can lead to maladaptive traits

three broad types

1. Historical constraints

2. Developmental/genetic constraints

3. material constraints

Historical constraints to evolution

The adaptive potential of a population depends on the history of that population

• genetic drift

• disequilibrium

• local and global optimal adaptations

Genetic Drift

Changes allele frequencies through random chance, normally decreasing variation

Populations can crash and rebound, creating small populations that can have issues with sample variation

Drift causes unpredictable evolution, isolated populations become genetically different from one another, variation increases

can result of fixation (even of maladaptive traits)

Fixation

All individuals of a population have identical alleles at a locus

Founder Effect

Establishment of a new population by a few orignal females, which only carry a small fraction of the total genetic variation of the parental population

• diseases are often more common due to inbreeding

Disequilibrium

Selection produces optimal adaptations only at equilibrium. Populations may continue to undergo selection after reaching ‘optimal adaptation’

Human diets currently include fat, salt, and sugar, which our bodies aren’t actually adapted too

Local vs Global optima

Selection is myopic

• small improvements to existing phenotypes based on which one increases fitness

• existing phenotypes are a function of phylogenic history

• changes occurs until an optimum is reached

  • reaching another optimum would only happen by reducing fitness, therefore will not happen.

An optimum may only be local, not global

Developmental Constraints

Variation is patterned by normal genetic and developmental processes

• some will be used multiple times pver the course of ones development

• genes that affect multiple aspects of the phenotype are pleiotropic - causing certain characters to be corrolated

Material Constraints

Adaptive potential is limited by the laws of chemistry and physics

requires organisms to be able to function properly in their environments

• diffusion ans surface/volume ratios

• gravity

• fluid dynamics

Species Concepts

Species are basic units of analysis for macroevolution, individuals belonging to a species are similar to one another, distinct from others.

We usually have an intuitive sense of what species are, but can be difficult to define

Biological Species Concept (BSC)

Most popular definition among evolutionary biologists

Species = a group of acutally or potentially interbreeding organisms that is reproductively isolated from other groups

Reproductive isolation

Individuals who cannot mate successfully outside group

• isolating mechanisms (geographic separation, differences in behaviour, physical appearance, #chromosomesl reproductive physiology)

• No Hybridiaztion - or hybrids die/are sterile

• Creates a barrier to gene flow between species

Probelms with BSC

Many clearly distinct species are not reproductively isolated,

some species are easy to define, others are not.

Humans like to put things in boxes, nature doesn’t care about our boxes

Speciation

Appearance of new species

but is often difficult to study

• occurs to rapid to show up in fossil record, while usually working to slow to observe in living pops

Anagenesis or Cladogenesis

Allopatric Speciation

Geographic spearation; non-overlapping ranges - reproductive isolation

two or more populations of a single speices become isolated geographically and then to form two+ new species

Truely tested if/when the isolated populations meet up again, if they cannot mate, they are different species

Character Displacement

Competition for resources will promote greater morphological differences (niche separation)

competition may lead one group to shift their habitat to one with less competition.

If no geographic overlap is present (no competition either) two species can have similar traits (diets, etc)

Reinforcement

Parents initially adapted to different environments, hybrid offspring can have a wide range of traits from each parent that makes them less fit for either environment

• hybrid offspring have lower fitness - less viable therefore reducing interbreeding

Parapatric Speciation

Limited overlap in ranges - no true barrier, but groups in different parts experience different environments

at overlap, hybrids will be selected against, keeping interbreeding low due to the waste of resources

Sympatric Speciation

Largely hypothetical,

Overlapping ranges, with differences arrising usually due to disruptive selection - different adaptations to the same environment

Ecological niche

How a species exploits/works within its habitat

• varies according to food, space, time

Adaptative radiation

occurs when a species colonizes a new habitat with many open niches

• fewer competitors, speices differntiate to fill empty niches quickly

Phyletic Gradualism

Tiny changes accumulate gradually via microevolution

gradual transformation from one species into another

rates of evolution are constatn and slow

Anagenesis

Punctuated Equilibrium

Short periods of rapid change after long periods of little or no change (Stasis)

New species arise through splitting isolation

Often fast

Cladogenesis