Arc 1: Midterm Prep Anthropology

Arc 1: Evolution

Darwin + The Darwinian Revolution

Monday September 9th, 2024

Pre-darwinian Assumptions

  1. Creationism

    1. What is creationism?

  2. Young Earth (4004 BCE - 6004 BCE)

  3. Great chain of beings

  4. Grand Design

    1. Everything was made on purpose by an intelligent designer

  5. Typological / Essentialistic thinking

    1. Species have an “essence” / there’s a type of animal with minor differences between

  6. Fixity / Stability / Immutability of species

    • Species don’t change

  • Key question to study: what were the pre-darwinian assumptions? Explain each and how it shaped the world? How does this relate to how colonialists felt about conquering the world and how were fossils explained back then?

Setting the Stage

Rumblings on fixity

  1. Buffon [1707-1788]

    1. He said that the geography & environment played a role in variation

    2. Don’t just name and classify, try to explain the patterns behind

  2. Erasmus Darwin [1731-1802]

    1. Transmutation of one species into another

    2. Longer history of earth

  3. Lamarck [1744-1829]

    1. First true evolutionist

    2. Really tried an explanation, not just a suggestion

    3. He explained the idea of inheritance of acquired characteristics

      1. A “favorable” characteristic gets passed on

Explaining extinct life forms

  1. Cuvier [1769-1832]

    1. Was a young earther

      1. Introduced the idea of catastrophism

      2. Events like “Noahs flood” contributed to the fossil record

  2. Lyell [1797-1875]

    1. Uniformitarianism (what was this?)

    2. Geology can be good by itself without theology

      1. Not talking yet about the biological world

    3. Hints at the idea of a long period of biological time

In another vein

  1. Malthus [1766-1834]

    1. Proposed the idea of struggle for existence.

      1. Starts sounding very similar to “survival of the fittest”

    2. Noted that populations should double every year but they don’t

      1. There’s something that keeps them on check

Charles Darwin

The man

  1. Darwin [1809-1882]

    1. Did a trip around the world in the HMS beagle

    2. After coming home he found differences in beak size

    3. 233 variations of capybaras

    4. Reading Malthus is pivotal to Darwin

    5. Darwin sits on its paper for 16 years

    6. He picks up on the practices from animal breeding

      1. There was an “artificial” selection

      2. In evolution he said, “nature” does the selection

Alfred Russel Wallace [1829-1913]

  • Wallace also observed the patterns of evolution but in Australia

  • He also was influenced by Malthus

Changed Assumptions

  1. Biology is not explained by creationism

  2. Older earth

  3. No great chain of being

    1. Man pulled back into the natural world

  4. No gran designer

  5. No fixity / No stability / Transmutation of species

  6. Populational thinking

    1. No inherent essence

    2. Variation is everywhere

Reactions then and now

  • Darwin is just a midpoint in the revolution

  • Sparked to the study call to explain variation

    • Led to the discovery of mitosis and meiosis

  • “Nothing in biology makes sense except in the light of evolution”

  • Key questions to internalize: who were the people that influenced Darwin and in what way? How did the assumptions of biology and science changed after Darwin? Why is it said that Darwin is just a midpoint in the revolution?

Evolutionary Forces - What are they and how they operate

Wednesday September 11, 2024

Introduction - what is evolution

  • In one word “change”

  • Evolution is a change in the genetic composition of a population over time

    • An increase in frequency % of a genotype

    • A genetic trait becomes more common in a population

  • Unit of evolution is the population [Hardy-Weinberg formula]

    • Population: a group of individuals likely to reproduce with each other

  • What causes the change?

    • EVOLUTIONARY FORCES

      • Mutation

      • Migration

      • Genetic drift

        • Founder effect

        • Bottleneck

        • Sampling error

    • The effects can be random or systematic

      • Random: in no specific direction

      • Systematic: in a specific direction or pattern. Driven by a clear advantage or purpose.

Evolutionary forces

Evolutionary Force

Definition

Effect

Optimal population size

Impact on variation within population

Impact on variation between population

1. Mutation

Change in DNA composition

Random

Large

⬆ small increase initially

⬆ small increase initially

2. Migration (gene flow)

Movement of genes between populations

Systematic

Small

Increases, more diversity of traits is introduced

Decreases, both populations become more similar

3. Genetic drift

When a genetic trait gets selected but for no advantageous reason

1. Sampling error: error due to small sample size doesn’t follow bell curve distribution (all female kids)

2. Bottleneck: when in the sample a trait survives for a random reason (color blindness in an island)

3. Founder effect: when a small part of a population starts a new one.

Random

Small

Decrease, only some traits get selected and the population becomes more similar

Increases, the populations become more different

4. Natural selection

Obtain traits that give you an advantage to survive

Regional and timely

Systematic

Large

Decreases, the ones that don’t survive and are different die

Increases, the populations start to look more different

Types of Selection

  1. Balancing / Stabilizing / Normalizing

    1. Selects for the middle of the bell curve

  2. Directional selection

    1. Selects for one extreme of the bell curve

      1. If the environment changes in one direction or another, that extreme will be favored.

      2. For example, if it got colder, those within the bell curve extreme with cold adaptations will survive (fur, more fat, etc…)

  3. Diversifying selection

    1. Both extremes of the bell curve get selected

      1. For example, the anoles that survived in different parts of the trees.

      2. In an island with only small and large seeds, the birds with middle sized beaks would dissappear.

Group and individual selection

  • The traditional view is that the unit of selection is the “individual” organism

    • Genes that help the individual survive are selected

  • It’s being challenged by the view that the unit of selection is the “group”

    • Genes that help the group survive are selected

  • Key questions to internalize: can you apply and do an analysis of which evolutionary forces are involved in different case studies? Don’t forget about the lecturette

Patterns of Micro and Macro Evolution

Monday September 16, 2024

Introduction

  • Ear wax example

    • Most people have wet earwax but some have dry and flaky earwax, why is that?

      • Natural selection might have occurred, prevents bug and mud from coming inside in hot humid places, presenting an advantage

      • Systematic because it follows a direction and a normalizing selection

Micro + Macroevolution

  • Microevolution: happens within short time frames

  • Macroevolution: Changes in large time frames

The modern synthesis

  • Combination of Mendelian genetics and Darwin.

  • Traditional view

    • Evolution is guided by small genetic changes guided by natural selection

    • Natural Selection is the most important force

      • The composer of evolutionary change

    • Macroevolution is a magnification of microevolution events

      • Opportunistic

        • Takes advantage of any genetic trait that helps the organism survive

      • Irreversible

        • Thought that once a trait was acquired it didn’t go back

      • Not directed

        • No goal, just a continuous process of adapting to a changing environment

What is a species? + How do we get new ones

Initial definition of a species

  • The biological species concept (BSC) [Ernest Mayr 1904-2005]

    • Group of interbreeding organisms that is reproductively isolated from other groups

    • Populations that don’t reproduce with other populations

      • To what extent does that apply? If I don’t like a certain physical characteristic or ideology and I wouldn’t want to reproduce would that make me a different species?

Modes / Models of speciation

  • How new species form

  1. “Allopatric” speciation

    1. Geographic barrier involved

      1. Natural selection changes each population

      2. There has to be some kind of selective pressure in either side

      3. Now they wouldn’t interbreed even if they meet because of so many differences

    2. “Allo” = other, “patria” = homeland

      1. Occurs when populations are in different places

  2. Parapatric speciation

    1. No geographic barrier involved

      1. Populations start to become separate, could be due to low mobility, and genetic drifts starts accumulating

      2. Also, there could be varying selective pressures across a range

        1. For example, there were different selective pressures in different parts of the tree and different lizards evolved

  3. “Sym” = together / same, “patria” = homeland

    1. Occurs when populations live in the same area

    2. Normally associated with host-parasites

      1. For example, in some lakes parasitic lice infest different species of cichlid fish leading them to become specialized on their type of host and become reproductively isolated from other fish

Reproductive Isolating Mechanisms (RIMS)

  • Ways in which two species stop interbreeding

  • They are generally a byproduct of genetic, ecological or behavioral divergence between populations

Premating RIMS

  1. Habitat

    1. They prefer to be in different habitats

      1. Top of the tree vs. bottom of the tree

      2. They will never meet and breed

  2. Seasonal

    1. They like to mate in different seasons

      1. Some might like to mate in spring, while others in summers

      2. Day person vs. night person

  3. Behavioral

    1. Different behaviors

      1. For example, there can be some behavior that totally turns you off

      2. People who have different “mood musics”

  4. Mechanical

    1. The parts don’t fit

Post-mating RIMS

  1. Gamete mortality

    1. Sperm and egg don’t meet

  2. Zygote mortality

    1. Doesn’t survive to birth

  3. Hybrid mortality

    1. Doesn’t live to reproductive age

  4. Hybrid sterility (partial or complete)

    1. The offspring can mate but not reproduce

      1. Partial: the hybrid has some reproductive ability, though reduced

        1. Ligers: male lion + female tiger

      2. Complete sterility: The hybrid is fully infertile

        1. Mules: male donkey and female horse

The results of speciation

Generalized + specialized forms

  • Generalized Forms: Species that adapt to a wide range of environments or niches.

    1. Often more flexible in their behavior, diet and habitat use.

    2. Rats, cockroaches, humans

    • Specialized Forms: Species highly adapted to a specific environment

      1. Tend to have a limited diet, specific habitat requirements, often depend on a single resource or specific conditions for survival

      2. Vulnerable to environmental changes but highly competitive in their niche

      3. Pandas highly specialized because they primarily eat bamboo

      4. Koalas rely mainly on eucalyptus, they die if they eat lettuce

Homologous / Analogous traits

  • Homologous: similarities between species due to a common ancestor

    • Analogous: Similarities due to adaptation to similar environment or function

      1. Wings formed in bees and birds to adapt to the air

Patterns of evolutionary change

  • Adaptive Radiation

    1. Repeated speciation / diversification from ancestral form

    2. Depends on opportunity + adaptive potential

      1. Opportunity: availability of new or unoccupied ecological niches

        1. Colonization of new environments

        2. Mass extinctions that wipes out dominant species

      2. Adaptive potential: species genetic ability to adapt and diversify

        1. Species that breed more often and have more offspring have more potential

        2. Genetic variation and flexibility in traits (ex. beak shape in birds=

    • Divergent Evolution

      1. Diverging from a common ancestor

    • Convergent Evolution

      1. Ancestor in distant past

      2. Convergent evolution refers to when unrelated species independently develop similar traits due to similar environmental pressures,

        1. Sharks (fish) and dolphins (mammals) developed a similar body shape and fins to adapt to the same environment

      3. As with parallel evolution, it’s the independent development of similarities in different regions

    • Parallel Evolution

      1. Ancestor in recent past

      2. Two related species evolve similar traits independently of each other, often because they experience similar environments or selective pressures after they diverge from a common ancestor

        1. Sabertooth cats and the marsupial sabertooth

          1. Both groups evolved elongated canine teeth and similar body structures independently despite being from different mammal lineages

          2. They evolved in parallel due to the similar selective pressure of being large predators that used their teeth for killing prey

  • Key questions to consider: what is the difference between macro and microevolution? What is the modern synthesis and its characteristics (views on evolution)? What is a species? What are the RIMS and when can they occur? What is the difference between post-mating rims and premating rims? What are the different types of RIMS for pre and post mating, describe each one of them? What are the different modes of speciation and describe them? What are the results of speciation? What types of similar traits can result? What are the patterns of evolutionary change and describe each one of them?

Challenges to the modern synthesis

Wednesday September 18, 2024

  • Quick recap of traditional view of modern synthesis

    • Natural selection is the composer of evolutionary change

    • Macroevolution is an extrapolation of microevolutionary events

Which is the most important evolutionary force?

  • “The battle over the “primate movers” of evolutions

  • Seleccionists vs Mutationists

    • The difference is just which force they emphasize more, it’s a matter of perspective.

    • Although not mentioned, in my opinion mutationists might view selective breeding, artificial selection or genetic engineering as evolution while selectionists don’t because it’s not selected by “nature”.

  • Neutral Theory of Evolution [Kimura, King, James]

    • Some DNA sequences or genes have mutations without any increase in fitness and are passed on, mostly due to genetic drifts or random mutations

    • In mutation driven evolution [Nei], the focus is on how novel mutations create new genetic material and selection acts later to eliminate harmful changes

Critique of the Adaptationist Program

  • beware of a “Panglossian view” (everything happens for a reason)

  • While trying to explain everything you might be explaining “spandrels”, or byproducts of adaptation

    • For example, the Cathedral of San Marco in Venice had arcs but it also had spandrels that were not intentional but byproducts of that architecture

The tempo and mode of evolutionary change

Traditional View

  • Mode: anagenesis

    1. “Ana” = up, “genesis” = origin

    2. Slow gradual change

    3. Changes in an entire species – without splitting

    4. There are arbitrary divisions between species

    5. So anagenesis means that a population has slow gradual changes and that’s how they evolve but they can keep interbreeding with themselves, there’s no speciation.

      1. It’s just the addition of changes of a population with time.

    • Overall pattern: phyletic gradualism

      1. “Phylon” = tribe / race.

        1. Refers to lineages

        2. Evolutionary changes that occur within a single lineage over time without branching out into multiple species

Alternate View

  • Mode: cladogenesis

    1. “Clade” = branch, “genesis” = origin

    2. Discrete beginnings / Clear distinction between species

      1. When a species splits, each one starts with a distinct, separate origin

    • Overall pattern: punctuated equilibria

      1. Periods of small or no change (equilibria), with sudden periods of splitting

Which one is correct?

  • Punctuated equilibria [Gould] has been accepted by an unambiguous and incontrovertible majority

  • Gradualism [Allen] is widely accepted as the most important and prevalent type of evolution

  • No one denies either, the questions is which is the most prevalent pattern

    • Apparently gradualism is the most prevalent

    • We’ll have to solve later, based on the fossil record, which mode of evolution is happening?

Relationship between macro & micro evolution

  • In the traditional view (according to gradualism), macroevolution might just be a corollary / extension of microevolution.

    • Microevolution stretched out = macroevolution

  • If punctuated equilibrium accurately describes microevolution - with its slow, gradual change or periods of stasis (lacks) it cannot explain the sudden bursts of branching and rapid speciation that define the macroevolution model

    • So decouple them and study them separately

Recent challenges

EvoDevo - Evolutionary Development

  • EvoDevo is what happens during development to the individual. The changes in developmental genes can lead to evolutionary differences between species.

    • If a mutation occurs of a developmental gene controls limb growth during development, that can lead to evolutionary changes in body structure.

Ecology and impact of organisms in their environments

  • You change your environment, your environment changes you

    • Certain species of ants construct construct underground colonies, modifying the soil and the microenvironment around them

      • These changes influence moisture levels, temperature, and the availability of nutrients

      • Over time, the environment inside and around these colonies selects for ants that are better adapted to these newly created conditions leading to evolutionary shifts in the ant population

Non-genetic or soft-inheritance / Epigenetics

  • Inherited stuff (altered regulation of genes but no actual change in the genes= f from what happened to their during parents during their lifetime

In Sum …

  • For some the synthesis is flexible enough to include these new views

  • For others, the synthesis is an “aging, decrepit beast” and a new paradigm is needed

  • It’s up to you to decide your stance

    • [Won’t be asked your opinion on the exam]

  • Key questions to consider: what were the characteristics of the modern synthesis or its view on evolution? What does the modern synthesis think is the main force for evolutionary change and what challenges arose? What do those challenges of the main force say? What are the tempo and modes of evolutionary change? Which tempo and mode is the traditional and which one is the alternative? Which of the tempo and modes is correct? Which one is more prevalent? Do they deny each other? Using the fossil record describe which mode is present? What is the traditional and alternate view on the relationship between micro and macroevolution? What have been other recent challenges, describe them?

Classification, systematics & the ordering of nature

Wednesday September 18, 2024

Introduction: why classifying + the tie to science

  • Systematics: the all encompassing study of classifying life

A note on Liminality (Gray areas)

  • Liminal / anomalous

    • Liminal: things that exist on the boundaries or in gray areas in established categories. Don’t fit neatly into one classification or another.

    • Anomalous: refers to things that don’t conform to what’s typical or expected within a given classification. These are outliers or exceptions that don’t easily fit into predefined categories

    • When something is liminal or anomalous, how you choose to classify reveals more about you, the classifier

      • Reflects our perspectives, priorities and limitations

        • Scientist bring their own understanding, cultural biases, and assumptions into the process

        • Classification systems are, to some extent, subjective or shaped by human perspectives

        • For example, a box of 64 crayons people will choose to classify it differently

        • In some cases people might push something fit into an existing category, even if it doesn’t quite belong there because they don’t want to create a new category. In other cases, the liminal or anomalous case might force the classifier to create a new category or reconsider the structure of the classification system itself.

Taxonomic Philosophies / Schools

Evolutionary / Orthodox Taxonomy

  • Phylogeny → “Ancestor descendant relationships”

    • Phylogenetic approach

    • Focuses on homologous character complexes

    • Weights traits – some more important than others

      1. Uses grades

    • Considers unique traits

Phenetic / Numerical Taxonomy

  • [Sokal & Sneath]

    • Group not by evolutionary relationships instead grouping by overall similarity

      1. Phenetic approach would group a lizard and croc together, but a bird separately

      2. Cladistic approach would group croc and bird together because they share a more proximate common ancestor than the lizard.

Cladistic / Phylogenetic Taxonomy

  • Cladistic is NOT related to cladogenesis

    1. Cladistic is classifying by common ancestry

      1. Seeks to reflect phylogeny

    2. Uses clades, groups that reflect the last common ancestor

      1. Chimps and humans under the same clade

      2. Evolutionary taxonomists would place the chimp with the orangutan and gorilla because they weigh based on who’s in the zoo vs who goes to the zoo.

        1. The difference is how close they place the humans to the chimps

        2. Actually the chimp and human are more closer than chimp & gorilla

  • Which classification tree you use depends on your goals & methods, for example if you are doing a

  • Unclear still: what is an ape? Where are they classified and at what level? What taxonomic school do they belong to? What was a prosimian and why might it look a bit outdated?

  • Key questions to consider: what is systematics? What is liminality and anomaly and why are they important to have them in consideration when viewing classification systems? What are the evolutionary taxonomies and describe them? What is the difference between a grade and a clade?