7.2.3 Common Ancestry, Speciation, and Extinction

Phylogeny/Cladogram

figure that shows the evolutionary relationships among organisms

“phylogenetic tree”

Leaves

Selected Taxa of phylogenetic tree

Root

point where the tree connects back to the rest of the tree of life

Node

most recent “hypothetical” ancestor

• all taxa are leaves → we cannot tell what true ancestors are

• even fossils will always be leaves

• We cannot distinguish ancestors from relatives

Speciation

the process of one species becoming two or more species

Species

Difficult answer: the smallest evolutionary unit

AP Bio answer: a grp of organisms that can interbreed (and create viable, fertile offspring)

Biological species concept

• requires reproductive barriers

  • Prezygotic barriers

    • prevents mating

  • Postzygotic barriers

    • prevents creation of viable, fertile offspring

Allopatric Speciation

new species appear in different areas

Vicariance

areas move

Migration

species move

Sympatric Speciation

New species appear in the same areas

Extinction

when all members of a species dies off

• sometimes opens up niche that new species can inhabit

Mass extinction

when a large percentage of Earth’s species die off at once

• 5 major ____ ____ events

• Humans might be causing the 6th

Adaptive Radiation

a rapid rate of speciation from a common ancestor, often associated with ecological and morphological diversity (Divergent evolution)

Gradualism

speciation associated with slow, gradual morphological changes

Punctuated Equilibrium

speciation associated with rapid morphological changes

Speciation-Extinction Equilibrium

a constant state of biological diversity

• speciation rate = extinction rate

cant tell if fossils could produce viable offspring/reproduce at all

BPQ

What are some problems with the biological species concept?