The secret of evolution What makes populations change?

First, let’s clear up how evolution does NOT happen.

“If humans evolved from monkeys, then why are there still monkeys?”

Because we didn’t 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 common ancestors. Not from each other.

Species & Speciation species species similar organisms that can interbreed in nature to produce fertile, viable offspring. similar organisms that can interbreed in nature to produce fertile, viable offspring. population population all the members of a species living in a defined area all the members of a species living in a defined area speciation speciation the generation of new, separate species from a single population the generation of new, separate species from a single population

Descent with Modification Microevolution Microevolution Genetic change in a population without the generation of new species Genetic change in a population without the generation of new species

Descent with Modification Microevolution Microevolution Natural populations show this type of variation, too. Natural populations show this type of variation, too.

Descent with Modification Macroevolution Macroevolution Genetic (and other) changes that split one species into two new species that can no longer breed to produce fertile, viable offspring. Genetic (and other) changes that split one species into two new species that can no longer breed to produce fertile, viable offspring. When two species cannot produce fertile, viable offspring they are said to be reproductively isolated from each other. When two species cannot produce fertile, viable offspring they are said to be reproductively isolated from each other. Reproductive isolation defines different species. Reproductive isolation defines different species.

Reproductive isolation ECOLOGICAL ECOLOGICAL Two species’ habitats are not compatible Two species’ habitats are not compatible (pre-zygote) (pre-zygote)

Reproductive isolation TEMPORAL TEMPORAL Two species’ mating times are different Two species’ mating times are different (pre-zygote) (pre-zygote)

Reproductive isolation BEHAVIORAL BEHAVIORAL Two species’ mating rituals not compatible Two species’ mating rituals not compatible (pre-zygote) (pre-zygote)

Reproductive isolation HYBRID INVIABILITY HYBRID INVIABILITY Two species’ hybrid offspring can’t survive Two species’ hybrid offspring can’t survive (post-zygote) (post-zygote) X = X

Reproductive isolation HYBRID STERILITY HYBRID STERILITY Two species’ hybrid offspring can’t reproduce Two species’ hybrid offspring can’t reproduce (post-zygote) (post-zygote)

But How? 1. MUTATION 1. MUTATION The raw material of evolution The raw material of evolution Piglet with a mutation causing holoprosencephaly Piglet with a mutation causing holoprosencephaly

But How? A mutation is a change in the DNA A mutation is a change in the DNA Before a cell divides, it copies its DNA Before a cell divides, it copies its DNA

But How? Sometimes, an error—called a MUTATION—is made. Sometimes, an error—called a MUTATION—is made.

But How? Recall how genes encode information… Recall how genes encode information…

But How? Every three “letters” on the DNA stands for one amino ac id Every three “letters” on the DNA stands for one amino ac id The three-letter codes of mRNA (made from DNA) are called CODONS The three-letter codes of mRNA (made from DNA) are called CODONS

But How? We now know which codons represent which amino acids! We now know which codons represent which amino acids!

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 acids in a protein, you change that amino acid or protein. If you change the identity or order of amino acids in a protein, you change that amino acid or protein. That’s called MUTATION. That’s called MUTATION. Let's see how this happens and what it means. Let's see how this happens and what it means. Let's see how this happens and what it means. Let's see how this happens and what it means.

Mutation Mutation is the “raw material” of evolution. Mutation is the “raw material” of evolution. Without different forms of genes and traits, there can be no evolution. Without different forms of genes and traits, there can be no evolution. All organisms would be exactly the same. All organisms would be exactly the same.

Mutation (A group of genetically identical organisms is a CLONE.) (A group of genetically identical organisms is a CLONE.)

Mutation The form found most often in a wild population is called the WILD TYPE. The form found most often in a wild population is called the WILD TYPE. Any form different from that is said to be MUTANT. Any form different from that is said to be MUTANT.

But How? 2. SMALL POPULATION SIZE 2. SMALL POPULATION SIZE Random changes will have stronger effect. Random changes will have stronger effect. This is known as GENETIC DRIFT This is known as GENETIC DRIFT

But How? 3. MIGRATION 3. MIGRATION Separate populations share genes and mutations. Separate populations share genes and mutations. These effectively become small populations. These effectively become small populations. And that means genetic drift. And that means genetic drift.

But How? 4. NON-RANDOM MATING 4. NON-RANDOM MATING POSITIVE ASSORTATIVE MATING POSITIVE ASSORTATIVE MATING Similar individuals pair off more often than expected. Similar individuals pair off more often than expected. Small effective population means… Small effective population means… GENETIC DRIFT GENETIC DRIFT

But How? 4. NON-RANDOM MATING 4. NON-RANDOM MATING NEGATIVE ASSORTATIVE MATING NEGATIVE ASSORTATIVE MATING Dissimilar individuals pair off more often than expected. Dissimilar individuals pair off more often than expected. Small effective population size means… Small effective population size means… GENETIC DRIFT GENETIC DRIFT

But How? 5. NATURAL SELECTION 5. NATURAL SELECTION Darwin’s theory Darwin’s theory

Natural Selection: Any trait can be… Adaptive – increases chances of leaving genes to the next generation. Adaptive – increases chances of leaving genes to the next generation. Maladaptive – decreases chances of leaving genes to the next generation. Maladaptive – decreases chances of leaving genes to the next generation. Neutral – does not affect chances of leaving genes to the next generation. Neutral – does not affect chances of leaving genes to the next generation.

Let’s consider some common misconceptions about evolution Misconception: Evolution is a theory about the origin of life. Misconception: Evolution is a theory about the origin of life.Evolution is a theory about the origin of life.Evolution is a theory about the origin of life. Here's some of the latest news. Here's some of the latest news. Here's some of the latest news. 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. A few people apparently didn't get the memo. A few people apparently didn't get the memo. A few people apparently didn't get the memo. Misconception: Evolution is a process by which organisms become "better". Misconception: Evolution is a process by which organisms become "better".Evolution is a process by which organisms become "better".Evolution is a process by which organisms become "better". Misconception: Evolution is the result of life changing by random chance. Misconception: Evolution is the result of life changing by random chance.Evolution is the result of life changing by random chance.Evolution is the result of life changing by random chance. Misconception: Organisms purposefully "try" to evolve traits because they need them. Misconception: Organisms purposefully "try" to evolve traits because they need them.Organisms purposefully "try" to evolve traits because they need them.Organisms purposefully "try" to evolve traits because they need them.

Misconception: Evolution means "survival of the fittest". Misconception: Evolution means "survival of the fittest".Evolution means "survival of the fittest".Evolution means "survival of the fittest". Misconception: Evolution is "just a theory". Misconception: Evolution is "just a theory".Evolution is "just a theory".Evolution is "just a theory". Misconception: Even the scientific community can't agree on how evolution works. Therefore it's a bogus idea. Misconception: Even the scientific community can't agree on how evolution works. Therefore it's a bogus idea.Even the scientific community can't agree on how evolution works.it's a bogus idea.Even the scientific community can't agree on how evolution works.it's a bogus idea. Misconception: Gaps in the fossil record are a major problem for evolutionary theory. Misconception: Gaps in the fossil record are a major problem for evolutionary theory.Gaps in the fossil record are a major problem for evolutionary theory.Gaps in the fossil record are a major problem for evolutionary theory.

Misconception: Evolutionary theory has failed to explain everything about how life originated and how it evolved. Misconception: Evolutionary theory has failed to explain everything about how life originated and how it evolved.Evolutionary theory has failed to explain everything about how life originated and how it evolved.Evolutionary theory has failed to explain everything about how life originated and how it evolved. Misconception: Evolution can't be studied scientifically because it is not observable or testable. Misconception: Evolution can't be studied scientifically because it is not observable or testable.Evolution can't be studied scientifically because it is not observable or testable.Evolution can't be studied scientifically because it is not observable or testable. Misconception: Most scientists no longer believe Darwin's ideas about natural selection. Misconception: Most scientists no longer believe Darwin's ideas about natural selection.Most scientists no longer believe Darwin's ideas about natural selectionMost scientists no longer believe Darwin's ideas about natural selection Misconception: Believing that evolution happened leads to immoral behavior and mayhem. Misconception: Believing that evolution happened leads to immoral behavior and mayhem.Believing that evolution happened leads to immoral behavior and mayhem.Believing that evolution happened leads to immoral behavior and mayhem.

Misconception: Evolution by natural selection means that social Darwinism is natural and can't be avoided in human culture. Misconception: Evolution by natural selection means that social Darwinism is natural and can't be avoided in human culture.Evolution by natural selection means that social Darwinism is natural and can't be avoided in human culture.Evolution by natural selection means that social Darwinism is natural and can't be avoided in human culture. Misconception: Evolution and religion are incompatible. Misconception: Evolution and religion are incompatible.Evolution and religion are incompatible.Evolution and religion are incompatible. Misconception: Teachers should teach "both sides" of the argument and let students decide for themselves. Misconception: Teachers should teach "both sides" of the argument and let students decide for themselves.Teachers should teach "both sides" of the argument and let students decide for themselves.Teachers should teach "both sides" of the argument and let students decide for themselves. Misconception: Evolution is like a religion. Therefore, teaching it violates the First Amendment of the U.S. Constitution. Misconception: Evolution is like a religion. Therefore, teaching it violates the First Amendment of the U.S. Constitution.Evolution is like a religion.First AmendmentEvolution is like a religion.First Amendment

Next Time: Natural Selection We will be predators. We will be predators. We will prey upon beans. We will prey upon beans.