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.