Evo-Devo, Cooperation, Microbial & Human Evolution: Key Concepts & Fossil Evidence

Ontogeny

The development of an organism from embryo → adult.

Evo-Devo

The study of how developmental processes evolve and how changes in genes lead to new forms.

Homeotic genes

Genes that determine the identity & position of body parts during development. Mutations cause body parts in wrong places.

Hox genes

A subset of homeobox genes that map the anterior-posterior body axis; deeply conserved across animals.

Colinearity (Hox genes)

The order of Hox genes on the chromosome matches the order of body regions they control.

Regulatory enhancer

A DNA sequence outside the gene that controls when/where/how strongly the gene is expressed.

Gene duplication

Creates extra gene copies that can evolve new functions or divide labor.

Paralog

A duplicated gene that diverges from the original, often evolving new functions.

Subfunctionalization

Duplicate genes split the original gene's job between them.

Neofunctionalization

One gene copy keeps the old job, the other evolves a new function.

Homeosis

Transformation of one body part into another (e.g., legs instead of antennae).

Heterochrony

Evolutionary changes in timing of development.

Recapitulation

When somatic traits appear earlier or reproductive traits appear later than in ancestors.

Paedomorphosis

Adults retain juvenile traits (e.g., axolotl retaining gills).

Hamilton's Rule

Altruism evolves when: r × b > c. (Relatedness × benefit > cost).

Inclusive fitness

Total fitness = direct fitness + indirect fitness through helping relatives.

Direct fitness

Producing your own offspring.

Indirect fitness

Helping relatives reproduce.

Eusociality

Cooperative brood care, reproductive division of labor, overlapping generations (seen in bees/ants/termites).

Reciprocal altruism

Helping unrelated individuals with expectation of future return.

Badge of status

Physical traits showing dominance (paper wasps' facial patterns, sparrow bib).

Three evolutionary paths to cooperation

Kin selection, reciprocal altruism, group selection.

Why microbes evolve fast

Huge populations, short generation times, high mutation rates.

Four causes of evolution

Mutation, natural selection, genetic drift, migration.

Absolute fitness (W)

Number of offspring an organism produces.

Relative fitness

Fitness of one genotype compared to another.

Selection coefficient (s)

Difference in fitness between genotypes.

Syntrophy

Two species complete a metabolic reaction together (e.g., hydrogen transfer).

Experimental evolution

Studying evolution in real time in controlled lab conditions.

Why study human origins in Africa?

Most early hominin fossils have been found there.

Out-of-Africa vs Multiregional models

Out-of-Africa: H. sapiens evolved in Africa, spread later. Multiregional: Modern humans evolved simultaneously in multiple regions from H. erectus.

Leaky Replacement Model

H. sapiens evolved in Africa but interbred with Neanderthals/Denisovans.

Sister group to humans

Chimpanzees and bonobos.

Physical differences: Neanderthals vs humans

Neanderthals = stockier, stronger, larger brow ridge, larger eyes.

Homo species that survived most recently (besides sapiens)

Homo floresiensis.

Levallois technique

Sophisticated stone flake production used by Homo heidelbergensis.

Bipedalism evolved before what?

Before large brains.

Conditions favoring fossilization

Rapid burial in soft sediment, low oxygen.

Background extinction

Normal, gradual extinction rate over time.

Mass extinction

Large, rapid loss of many species globally.

Permian Extinction cause

Massive volcanic eruptions → climate change, ocean anoxia. 'The event where life almost died.'

K-Pg extinction cause

Asteroid impact 65 mya.

Endemic species

Species native to one geographic area only.

Law of superposition

Deeper fossils are older.

Radiometric dating

Uses decay of isotopes to determine age.

Phyletic gradualism

Slow, continuous evolutionary change.

Punctuated equilibrium

Long periods of stasis + short bursts of rapid change.

Embryonic stage where groups are least similar?

Stage 4.

With recapitulation...?

Somatic earlier; reproductive later.

Totipotent cell?

Can differentiate into any cell.

What are the characteristics in the figure?

Evo-devo.

Paralog?

Duplicate of an existing gene.

True statement (neural crest / tube)?

All chordates have a neural tube.

Field that studies development + evolution?

Evolutionary developmental biology.

Mass extinction that killed dinosaurs?

K-Pg.

Human evolution diagrams A & B show?

Multiregional vs Out-of-Africa. (A = multiregional; B = out-of-Africa.)