Bio Unit 4 Intro to Evolution

Creation Evolution Positions

A scientific creationism, Scientific creationism, Old Earth Creationism, Intelligent Design creationism, Evolutionary creationism, Theistic Evolution

Two books model

book of scripture and book of nature → God’s word and creation are both perfect and compatible

Book of Scripture

God's word, theological understanding/human interpretation

Book of Nature

God’s creation, scientific understanding

Darwin

Evolution through descent with modification

Events that led to Darwin's “On the Origin of Species”

Education: Medical school, Ministry, Naturalist on H.M.S. Beagle (1831

H.M.S Beagle

Observed regional similarity of organisms (island vs mainland), theory of Darwin's finches

Lyell

principles of Geology – age of geological formation of Earth, Earth looks old because it is old (impacted darwin)

Malthus

theory of limited resources and struggle for existence (impacted darwin)

Artificial selection

change can be observed in real time – chose to breed fancy pigeons (impacted darwin)

Descent with modification

newer organisms are modified descendants of older organisms, through natural selection they have the most favorable traits of older organisms

Alleles

responsible for variations in traits,

Differences in alleles

result in genetic variation

Sources of Genetic variation

Mutations, sexual reproduction (crossing

What causes changes in allele frequency

Natural selection, genetic drift, gene flow, mutations and non

Natural selection

individuals vary, and the “best” variants survive

Genetic drift

chance alteration of allele frequency, new population with different frequency develops from the mother population (can lead to loss of genetic variation)

Bottleneck effect

Type of Genetic Drift → by chance the population was reduced, reducing the gene pool

Founder effect

Type of Genetic Drift → establishes a new population on a small number of individuals

Gene flow

movement of genes from one population to another (through migration and pollination)

Mutations

chase change in allele frequencies

Non random mating

organisms choose mating

Assortative mating

organisms chose mate off of similar traits

Why natural selection is the only mechanism that consistently leads to adaptive evolution (change)

it increases the frequency of alleles that improve survival and reproduction.

Hardy Weinberg equilibrium Assumptions

No selection, gene drift, gene flow, mutation, and mating is random

Phenotypic evolution

Changes in phenotypic frequency (physical traits), due to changes in allele frequency. Happens naturally or artificially

Assumptions for natural selection

Phenotypic variation, Different number of offspring survive, Genetic basis for traits

Fitness

Ability to survive, mating success, number of offsprings

Negative Allele Frequency driving natural selection

more common phenotypes more preyed upon/rare phenotypes have higher fitness, maintains allele variation

Positive Allele frequency driving natural selection

having common phenotypes allows you to blend in/rare phenotypes have lower fitness, reduces genetic variation

Stabilizing Selection

intermediate/average traits favored, tall skinny curve in middle (Ex: Clutch size in robin’s nests)

Directional Selection

favors extreme phenotype at one end of the graph, curve shifts left or right (Ex: Tongue length in anteaters)

Disruptive Selection

both extreme traits favored (Ex: beak size in African seedcracker finches)

Limitations to natural selection

Lack of variation, historical constraint, trade offs, gene flow, pleiotropy

How guppies offer a modern example of natural selection

demonstrate how predator pressure influences traits and different environments favor different phenotypes.

Evidence for evolution

Natural selection, fossils, anatomy, convergent evolution, biogeographical record

Fossils

show species changing from one to another

Vestigial structures

Anatomy evolution evidence: structures that no longer serve function, but once did (Ex: pelvic bone on whale)

Homologous structures

Anatomy evolution evidence: anatomical features that share origin, but have different functions in different organisms (Ex: vertebrate forelimbs)

imperfect structures

Anatomy evidence for evolution: shows evolutionary randomness (Ex: backwards photoreceptors in human eyes)

embryonic development

Anatomy evidence for evolution: post anal tail and gills (Ex: present in both humans and chickens)

Convergent evolution

Anatomy evidence for evolution: unrelated organisms evolve similar adaptations based on similar selective pressures (Ex: streamline bodies in marine predators)

Biogeographical record

study of geographic distribution of species

Relative vs radiometric dating

Relative dating: based on how far down in the ground the fossil is Radiometric dating: based on carbon in fossil, and how many half lives it had decayed (using carbon 14 to carbon 12 ratios)

Phenotypic evolution

change of allele frequency within population → species is still the same but just looks or behaves differently

Speciation

change of one species to another → requires phenotypic divergence and reproductive isolation

Phenotypic evolution vs speciation

Phenotypic is variation within species, speciation is not the same species anymore

Morphological Species Definition

based on physical traits (similarities and differences)

Morphological Species Definition weakness

unclear boundaries, which traits are focused on → subjective

Phylogenetic Species Definition

smallest group of individuals that share a common ancestor are grouped as a species

Phylogenetic Species Definition weakness

how to know when to stop, how much difference is needed to classify, its ever

Biological Species Definition

species are groups of successfully interbreeding organisms. Ernst Mayer theory (ex dogs)

Biological Species Definition weaknesses

there are examples in nature of organisms that aren’t the same species interbreeding (liger)

Requirements for successful reproduction

separation of gene pools through pre or post zygotic barriers

Prezygotic barriers

prevention BEFORE fertilization

Types of prezygotic barriers

habitat, temporal, behavioral, mechanical and gametic isolation

Habitat isolation

two species separated by location

Temporal isolation

breeding at different times

Behavioral isolation

different courtship rituals

Mechanical isolation

incompatible reproductive parts

Gametic isolation

incompatible gametes (broadcast spawning)

Postzygotic barriers

prevention AFTER fertilization

Types of postzygotic barriers

reduced hybrid vitality and fertility, hybrid breakdown

Reduced hybrid vitality

short lived offspring who don’t survive long enough to reproduce

Reduced hybrid fertility

offspring are infertile (ex mules)

Hybrid breakdown

fertile hybrids w/ sterile offspring

What is required for speciation to occur

Phenotypic divergence and reproductive isolation

Causes of reproductive isolation

Genetic drift (Ex: Founder effect, Population bottleneck), Natural selection

Allopatric speciation

“other fatherland” geographic isolation (typically) (Ex: Little paradise king fischer)

Adaptive radiation

often follows allopatric speciation: rapid emergence of new species from single species introduced to a new environment

Character displacement

Often follows allopatric speciation: occurs when two otherwise ecologically distant species come together, natural selection favors organisms that can utilize different resources

Sympatric speciation

“same fatherland” occurs without geographic isolation (Ex: polyploidy in plants): Occurs through disruptive selection, if two distinct enough phenotypes are created

How gene flow can act against reproductive isolation

constantly mixing alleles between populations, preventing them from diverging enough to become separate species

The two major models on the timing of speciation

Gradual and Punctual

Punctual

periods of lots of change followed by periods of minimal change

How mass extinctions have been followed by sudden diversification

Mass extinctions are often followed by periods of rapid diversification as surviving lineages fill newly available niches.

Evidence for a 6th mass extinction

High extinctions per millions of species per year, rates that have corresponded to previous extinction rates

Monkeys vs Apes

If it doesn’t have a tail its not a monkey, Apes closest living relatives to humans

Hominims

species more related to humans than they are to chimps, have bipedalism, larger brains

Homo neanderthalensis vs Homo sapiens

homosapiens more imaginative, creativity, social attachment, belief, neanderthals had shorter stockier bodies and larger brains

Evidence for the Out of Africa” theory

Early Homo sapiens fossils from Ethiopia (~195,000 years old), A clear timeline of migration out of Africa between 85,000–55,000 years ago, Global dispersal patterns consistent with fossil and genetic data

Melanin

drives skin color variation

High melanin

protects against UV radiation and folate degradation

Low melanin

allows sufficient UV absorption for vitamin D synthesis

Driving force of natural selection

Negative/Positive allele frequency, Directional/Disruptive/Stabilizing selection

Definitions of Speciation

Morphological, Phylogenetic, Biological (Ernst Mayer)

Reproductive Isolation Mechanisms (Required for Speciation)

Prezygotic and Postzygotic mechanisms

Causes of Reproductive Isolation

Genetic drift, natural selection

Mechanisms of Speciation

Allopatric (Character Development and Adaptive Radiation) and Sympatric

Old World Monkey

Arboreal + ground dwelling, down nostrils, no prehensile tail

New World Monkey

All arboreal, side nostrils, all prehensile tail

Homo

Defined by larger brains

Hominid

Broad category encompassing all the great apes