Chapter 18: Introduction to Darwinian Evolution

Convergent evolution

organisms evolved similar characteristics as a result of exposure to similar environmental challenges [natural selection]

Homologous

two different related species share a common ancestor with different adaptations of common ancestral feature

Homoplasy

two different, unrelated species that do not share a common ancestor share similar traits

Macroevolution

major evolutionary changes that occur over a long period of time resulting in large phenotypic changes such as the formation of new species

Microevolution

more minor evolutionary changes that occur over just a few generations (allele level)

Modern synthesis     

an explanation of evolution that incorporates many aspects of biology such as molecular genetics, phylogeny, natural selection, mutations, etc.

Population    

a group of individuals of the same species

Species

a group of successfully interbreeding organisms that also produce fertile offspring that interbreed

Vestigial structure

remnants of structures that were present and functional in the ancestral organisms

Two species have homologous structures. What can we infer?

A.) The structures are identical

B.) The structures have the same function

C.) The species have very different ancestors

D.) The species are related by a common ancestry

E.) The structure have the same function, and they are identical

D.) The species are related by a common ancestry

Natural Selection

Mechanism where organisms with best chance of survival pass on their genes

Evolution

gradual change in traits over time (accumulation of heritable traits)

-modifications can occur in just a few generations

Things to keep in mind with respect to evolution (4)

-organisms survive as a result of changes that occur in gene pool

-do not change to survive

-modifications or changes may not result in a more complex or ordered state

-natural selection favors genetic change supporting survival

(two population may diverge to the point of becoming different species )

Biological species are similar organisms capable of two major things

interbreeding and producing fertile offspring

Population

is a group of individuals of one species (live in same geographic area at same time)

Leanardo da Vinci

fossils as extinct animals/organisms

Hutton

Gradualism

Curvier

punctuated equilibrium

-catastrophes= mass extinction → new species fill void

Malthus

geometric vs arithmetic growth

-favorable variations for survival tend to be preserved, unfavorable ones eliminated

Jean Baptiste de Lamarck

traits acquired during one’s lifetime passed to offspring (natural phenomenon involved and evolutionary change occurs)

Lamarck

use vs disuse: extension of neck causes elongation so offspring will have longer neck

Darwin

(natural selection): variety of necks, longer necks

-reach higher leaves (one possibility)

-mate selection (males use necks to fight)

-heat regulation (vary amount of body surface in sun)

(genetic drift favors longer neck)

Darwin proposed that evolution occurs by natural selection based upon 4 observations…

-Variation: characteristics not same in all individuals in a population

-Overproduction: more offspring produced than can survive

-Limits on population growth: number of survivors limited by competition for resources

-Differential reproductive success (survival of the fittest): most favorable combination of characteristics likely to survive and reproduce

Explain the fossil record

• relationships/lineage/progression: connections between living and dead

• DNA analysis changing historical relationships (genetic relationships)

• Other fossil evidence (preserved footprints and embryos)

Homology Requirements

similar in origin, implies common ancestor: monophyletic

-diff species

-different adaptation/variation of common ancestral feature

-occurs as part of divergent evolution

Homoplasy: example

similar in appearance but not origin (same species, no common ancestor)

-birds compared to insects: vertebrate vs. invertebrate- wings (flight) evolved independently, not from a common ancestral feature

Analogous Structures

have a similar function but anatomically different

Homology Example vertebrates and mollusks

vertebrates: humerus→ ulna and radius

mollusks: foot for movement, anchoring, feeding

Convergent Evolution

(gives rise to homoplasy)

-similar natural selection pressure produce similar result (e.g. wings and flight)

Homology or Homoplasy

Homology: skeletal features (comes from common ancestor [both vertebrates])

Homoplasy: red in color (evolved separately)

Vestigial Structure

Remnants of past structure: overtime useful structure becomes smaller→ loss of function or may degenerate entirely

Vestigial Structure Examples (6)

-palmaris longus

-plica semilunaris (3rd eyelid blinks horizontally and still present in other animals)

-human fused tailbones, third molar wisdom teeth, muscles that move ears

-pelvic bones in other animals

-secum and appendix in humans

Explain

How and when genes are switched on and off during development results in diversity of form in species with similar genes

-fish, chickens, and humans are vertebrates (strikingly similar genes)

-different developmental pathways, different results (fins, wings, or limbs)