Transcript Major Trends in Evolution

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
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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.