Major Trends in Evolution

Microevolution Small changes over time in the allele frequencies within a species which could eventually lead to speciation Micro = Small

Macroevolution Large scale evolutionary changes that separate genera, families, orders, classes and even phyla of organisms Macro = Large

Patterns of Descent Evolution over time can follow several different patterns. Factors such as environment and predation pressures can have different effects on the ways in which species exposed to them evolve.

1. Gradual Change Direction selection towards a particular phenotype or genotype occurs very slowly

2. Divergent Evolution Speciation which results in 2 different species 2 populations diverge after being isolated Can occur via allopatric, parapatric or sympatric mechanisms

3. Adaptive Radiation Multiple divergence (speciation) which occurs more-or-less simultaneously. Many similar species arise from one common ancestor

4. Convergent Evolution Unrelated organisms (no common ancestor) evolve similar features due to environmental selective pressures Organisms have a common lifestyle or habitat Torpedo-shaped bodies for swimming in dolphins and sharks Wings for flight in insects, birds, mammals

5. Co-evolution 2 or more species affect one another’s evolution Plants and their insect pollinators Dodo birds and their food source Parasites and their hosts Predators and their prey

6. Parallel Evolution 2 similar organisms (with a common ancestor) evolve along similar lines due to living in similar environments with similar selective pressures. The 2 groups are isolated Sabre tooted cats, marsupial and placental mammals,

Name the Pattern of Descent

Gradual Change

Convergent Evolution

Adaptive Radiation

Co-evolution

Divergent Evolution

Parallel Evolution

Convergent Evolution

Trends in Microevolution Phyletic Gradualism vs. Punctuated Equilibrium

Phyletic Gradualism Darwin Gradual change over time Speciation occurs very slowly Gaps in the fossil record – many missing links or lack of transitional forms

Punctuated Equilibrium Eldridge and Gould Long periods of no change, punctuated by fairly large changes in a short time period Speciation occurs rapidly Explains why transitional fossils may not exist

It’s Story Time!! Read the information pages on Phyletic Gradualism and Punctuated Equilibrium Pick a number. Write a story for your assigned organism that parallels the story you read

Background for Evolution Stories Stripes and spots are for camouflage. Zebras are related to horses, they travel in herds and their predators are lions. They live in grasslands. Cheetahs are predators that have to chase their prey to catch it. They evolved from cougars who have plain coats. Snakes likely evolved from lizards who have legs. Snakes like to burrow beneath the ground.

Leopards are predators that have to chase their prey to catch it. They live in forests and are related to tigers. Pandas climb trees and use their hands to obtain their food (bamboo). Their thumbs are like human thumbs and allow for grasping. (See p.19 of your text book) Elephants trunks are modified noses. Aside from smelling, trunks can suck up water, rip leaves off branches and transfer these to the mouth. Rose thorns serve as protection against predators (herbivores that like to eat roses). Thorns are short sharp modified branches.