Patterns in evolution: 17-2, 17-4

Endosymbiotic theory

• Proposes that complex cells arose from smaller prokaryotes invading the larger eukaryotes.

• The cells that used oxygen to make ATP became mitochondria.

• Those that could photosynthesize became chloroplasts.

• Evidence: both contain DNA different from nuclear DNA

Sexual reproduction• Eukaryotic cells begin

to reproduce sexually.• The reshuffling of genes

greatly increases gene combinations and variation.

• This increased diversity and the speed of evolutionary change Tetrahymena thermophila

Multicellularism

• Began a few million years after sexual reproduction.• Life became multicellular, experiencing great diversity

over time.• All developed in the sea.• Because of their soft bodies, few fossils remain.

hydra microfossils

Big ideas of evolution: Extinction• 99% of all species once

living are now extinct• Most succumb to natural

selection• Mass extinctions have

several causes• Survivors experience a

burst of evolution, producing many new species

Diatrymas: 55-65 MYA stood 2 m tall

Adaptiveradiation

• A single species or a small group of species evolve into many diverse forms, living in different niches.

Anole lizards of theCaribbean islands

Convergent evolution

• Unrelated organisms can develop to look similar to others if they adapt to the same environment

• Ex: all species that swim in the water are streamlined, with paddles for locomotion

Shark, dolphin, and penguin representaquatic fish, mammal, and bird species

Coevolution

• Organisms that are closely connected often evolve together

• Occurs often in flowers and their pollinators• Plants evolve poisons to ward off insects that eat

them, who become immune over time.

Gradualism• The idea that

evolution happens at a slow, steady pace.

• Exception: horseshoe crabs have changed little from their fossils.

Punctuated equilibrium

• Evolution can proceed at different rates

• There can be long periods of stability, then brief periods of more rapid change

Developmental genes and body plans

• Master control genes guide the development of major body parts in animals

• Small changes in the expression of developmental genes can cause large changes in the adult

Antennapedia and wingless fruit flies

Plant and animal mutations

The human evolutionary tree