The The secret of secret of evolutionevolution

What makes What makes populations populations

change?change?

First, letFirst, let’’s s clear up clear up

how how evolution evolution does NOT does NOT

happen.happen.

““If humans evolved from If humans evolved from monkeys, then why are monkeys, then why are

there still monkeys?there still monkeys?””

Because we didnBecause we didn’’t t evolve from monkeys.evolve from monkeys.

Mushrooms don't evolve into pine trees.Mushrooms don't evolve into pine trees.

Fish don't evolve into amphibians.Fish don't evolve into amphibians.

Frogs don't evolve into reptiles.Frogs don't evolve into reptiles.

Reptiles don't evolve into birds.Reptiles don't evolve into birds.

Birds don't evolve into mammals.Birds don't evolve into mammals.

New species evolve from New species evolve from common ancestors.common ancestors.

Not from each other.Not from each other.

Species & SpeciationSpecies & Speciation• species species • similar organisms that can similar organisms that can

interbreed in nature to produce interbreed in nature to produce fertile, viable offspring.fertile, viable offspring.

• population population • all the members of a species living all the members of a species living

in a defined areain a defined area

• speciation speciation • the generation of new, separate the generation of new, separate

species from a single populationspecies from a single population

Descent with Descent with ModificationModification

MicroevolutionMicroevolution Genetic change in a population Genetic change in a population

without the generation of new without the generation of new speciesspecies

Descent with Descent with ModificationModification

MicroevolutionMicroevolution Natural Natural

populations show populations show this type of this type of variation, too.variation, too.

Descent with Descent with ModificationModification

MacroevolutionMacroevolution Genetic (and other) changes that split Genetic (and other) changes that split

one one species into species into two two new species that new species that can no longer breed to produce fertile, can no longer breed to produce fertile, viable offspring.viable offspring.

When two species cannot produce When two species cannot produce fertile, viable offspring they are said to fertile, viable offspring they are said to be be reproductively isolated reproductively isolated from each from each other.other.

Reproductive isolation Reproductive isolation defines defines different different speciesspecies..

Reproductive isolationReproductive isolation

ECOLOGICALECOLOGICALTwo specieTwo specie

ss ’’ habitats habitats are not are not compatiblecompatible

(pre-(pre-zygote)zygote)

Reproductive isolationReproductive isolation

TEMPORALTEMPORALTwo speciesTwo species’’ mating times are different mating times are different (pre-zygote)(pre-zygote)

Reproductive isolationReproductive isolation

BEHAVIORALBEHAVIORALTwo speciesTwo species’’

mating mating rituals not rituals not compatiblecompatible

(pre-(pre-zygote)zygote)

Reproductive isolationReproductive isolation

HYBRID INVIABILITYHYBRID INVIABILITY Two speciesTwo species’’ hybrid offspring can hybrid offspring can’’t survivet survive (post-zygote)(post-zygote)

X = X

Reproductive isolationReproductive isolation

HYBRID HYBRID STERILITYSTERILITY

Two speciesTwo species’’ hybrid hybrid offspring canoffspring can’’t t reproducereproduce

(post-zygote)(post-zygote)

But How?But How?

1. MUTATION1. MUTATION The raw material The raw material

of evolutionof evolution

Piglet with a Piglet with a mutation mutation causing causing holoprosencephholoprosencephalyaly

But How?But How?

A mutation is a change in the DNAA mutation is a change in the DNA

Before a cell divides, it copies its DNABefore a cell divides, it copies its DNA

But How?But How?

Sometimes, an error—called a Sometimes, an error—called a MUTATIONMUTATION—is —is made.made.

But How?But How?

Recall how genes encode information…Recall how genes encode information…

But How?But How?

Every three “letters” on the DNA stands for Every three “letters” on the DNA stands for one amino acone amino acidid

The three-letter codes of mRNA (made from DNA) are The three-letter codes of mRNA (made from DNA) are called called CODONSCODONS

But How?But How?

We now know which codons represent which We now know which codons represent which amino acids!amino acids!

But How?But How?

Each amino acid has a unique “personality”.Each amino acid has a unique “personality”.

If you change the identity or order of amino If you change the identity or order of amino acids in a protein, you change that amino acids in a protein, you change that amino acid or protein. acid or protein.

That’s called That’s called MUTATIONMUTATION..

Let's see how this happens and what it means.

MutationMutation

Mutation is the “raw material” of Mutation is the “raw material” of evolution.evolution.

Without different forms of genes and Without different forms of genes and traits, there can be no evolution.traits, there can be no evolution.

All organisms would be exactly the All organisms would be exactly the same.same.

MutationMutation

(A group of genetically identical organisms (A group of genetically identical organisms is a is a CLONECLONE.).)

MutationMutation

The form found most often in a wild The form found most often in a wild population is called the population is called the WILD TYPEWILD TYPE..

Any form different from that is said to be Any form different from that is said to be MUTANT.MUTANT.

But How?But How?

2. SMALL POPULATION SIZE2. SMALL POPULATION SIZERandom changes will have Random changes will have

stronger effect.stronger effect.This is known as This is known as GENETIC DRIFTGENETIC DRIFT

But How?But How?

3. MIGRATION3. MIGRATION Separate Separate

populations populations share genes and share genes and mutations.mutations.

These effectively These effectively become small become small populations.populations.

And that means And that means genetic drift. genetic drift.

But How?But How?

4. NON-4. NON-RANDOM RANDOM MATINGMATING POSITIVE POSITIVE

ASSORTATIVE ASSORTATIVE MATINGMATING

Similar individuals Similar individuals pair off more often pair off more often than expected.than expected.

Small effective Small effective population means…population means…

GENETIC DRIFTGENETIC DRIFT

But How?But How?

4. NON-4. NON-RANDOM RANDOM MATINGMATING NEGATIVE NEGATIVE

ASSORTATIVE ASSORTATIVE MATINGMATING

Dissimilar Dissimilar individuals pair off individuals pair off more often than more often than expected.expected.

Small effective Small effective population size population size means…means…

GENETIC DRIFTGENETIC DRIFT

But How?But How?

5. NATURAL SELECTION5. NATURAL SELECTION DarwinDarwin’’s theorys theory

Natural Selection: Natural Selection: Any trait can be…Any trait can be…

Adaptive Adaptive – increases chances of leaving – increases chances of leaving genes to the next generation.genes to the next generation.

Maladaptive Maladaptive – decreases chances of leaving – decreases chances of leaving genes to the next generation.genes to the next generation.

Neutral Neutral – does not affect chances of leaving – does not affect chances of leaving genes to the next generation. genes to the next generation.

LetLet’’s consider some common s consider some common misconceptions about misconceptions about

evolutionevolution Misconception: Misconception:

Evolution is a theory about the origin of life. Here's some of the latest news. On the origin of life…On the origin of life… A few people apparently didn't get the memo.

Misconception: Misconception: Evolution is a process by which organisms become "better".

Misconception: Misconception: Evolution is the result of life changing by random chance.

Misconception: Misconception: Organisms purposefully "try" to evolve traits because they need them.

Misconception: Misconception: Evolution means "survival of the fittest".

Misconception: Misconception: Evolution is "just a theory".

Misconception: Misconception: Even the scientific community can't agree on how evolution works. Therefore Therefore it's a bogus idea.

Misconception: Misconception: Gaps in the fossil record are a major problem for evolutionary theory.

Misconception: Evolutionary theory has failed to Misconception: Evolutionary theory has failed to explain everything about how life originated and explain everything about how life originated and how it evolved. how it evolved.

Misconception: Evolution can't be studied Misconception: Evolution can't be studied scientifically because it is not observable or testable. scientifically because it is not observable or testable.

Misconception: Most scientists no longer believe Misconception: Most scientists no longer believe Darwin's ideas about natural selection. Darwin's ideas about natural selection.

Misconception: Believing that evolution happened Misconception: Believing that evolution happened leads to immoral behavior and mayhem.leads to immoral behavior and mayhem.

Misconception: Evolution by natural Misconception: Evolution by natural selection means that social Darwinism is selection means that social Darwinism is natural and can't be avoided in human natural and can't be avoided in human culture. culture.

Misconception: Evolution and religion are Misconception: Evolution and religion are incompatible.incompatible.

Misconception: Teachers should teach "both Misconception: Teachers should teach "both sides" of the argument and let students sides" of the argument and let students decide for themselves. decide for themselves.

Misconception: Evolution is like a religion. Misconception: Evolution is like a religion. Therefore, teaching it violates the First Therefore, teaching it violates the First Amendment of the U.S. Constitution.Amendment of the U.S. Constitution.

Next Time: Natural Next Time: Natural SelectionSelection

We will be predators.We will be predators.

We will prey upon beans.We will prey upon beans.