SpeciationSpeciation

““Is that how organisms become Is that how organisms become special, Ms. Bass?”special, Ms. Bass?”

““Whatever!”Whatever!”

Review of Natural SelectionReview of Natural Selection

You’ve already You’ve already learned about learned about adaptations. Let’s adaptations. Let’s review by giving review by giving these some these some names.names.

Common AncestorCommon Ancestor

In other words, In other words, organisms that look alike organisms that look alike may have had a shared, may have had a shared, or common, ancestor in or common, ancestor in their past. Darwin their past. Darwin thought that the finches thought that the finches started with one type of started with one type of beak that adapted to beak that adapted to help them eat the food help them eat the food source on that island. source on that island. Here are some Here are some examples:examples:

Nature has three basic ways of choosing Nature has three basic ways of choosing what is a useful adaptation.what is a useful adaptation.

Directional Selection is Directional Selection is when nature chooses one when nature chooses one adaptation over another adaptation over another one. For example, which one. For example, which squirrel would stand out squirrel would stand out in the forest? Nature in the forest? Nature would choose the brown would choose the brown one because it can hide one because it can hide easier. Eventually, easier. Eventually, enough multicolored enough multicolored squirrels would be killed squirrels would be killed and it would no longer be and it would no longer be in the gene pool.in the gene pool.

Nature has three basic ways of choosing Nature has three basic ways of choosing what is a useful adaptation.what is a useful adaptation.

Disruptive selection is when nature chooses two extreme Disruptive selection is when nature chooses two extreme variations of a trait over one that is in between them. In variations of a trait over one that is in between them. In this case, the middle size goes away.this case, the middle size goes away.

Sammy Seal says the small one is too hard to open so he can live.

Sammy Seal says the big one fights too much so he lives.

Sammy Seal says this medium one is just right so he gets eaten tonight and won’t have any kids.

Nature has three basic ways of choosing Nature has three basic ways of choosing what is a useful adaptation.what is a useful adaptation.

Stabilizing selection is Stabilizing selection is when organisms are when organisms are chosen for being an chosen for being an average size. In this average size. In this case, the middle size case, the middle size stays. stays.

Too small

Too bigJust right

So then how are species So then how are species “made”?“made”?

Speciation is the process Speciation is the process that organisms take to that organisms take to become a new species. become a new species.

Remember that a species Remember that a species is a group of is a group of interbreeding organisms.interbreeding organisms.

There are two basic There are two basic reasons why species reasons why species would grow apart. Let’s would grow apart. Let’s look at them.look at them.

+

If you can’t breed If you can’t breed and make babies, or and make babies, or if you don’t have the if you don’t have the same process you same process you probably aren’t in the probably aren’t in the same species.same species.

Evolution of SpeciesEvolution of Species Geographic isolationGeographic isolation

When species are When species are separated by a physical separated by a physical barrier, it becomes hard to barrier, it becomes hard to breed.breed.

Eventually, the organisms Eventually, the organisms adapt to the ones around adapt to the ones around them and the organisms on them and the organisms on the other side of the barrier the other side of the barrier become foreign and form become foreign and form their own gene pool.their own gene pool.

This may cause the two to This may cause the two to no longer be able to breed no longer be able to breed together.together.

Evolution of SpeciesEvolution of Species Reproductive IsolationReproductive Isolation

When mating seasons or When mating seasons or structures change, it structures change, it interferes with how interferes with how organisms reproduce.organisms reproduce.

If fertile seasons are If fertile seasons are different, the organisms different, the organisms could evolve into two could evolve into two different species because different species because they will never have a they will never have a chance to mate or share chance to mate or share the same gene pool.the same gene pool.

If the reproductive If the reproductive structures aren’t structures aren’t compatible, the two compatible, the two organisms can no longer organisms can no longer reproduce together.reproduce together.

+ = ?

How does speciation happen?How does speciation happen?

There are two theories that discuss how species develop There are two theories that discuss how species develop over time:over time: Gradualism says that organisms have changed slowly and says that organisms have changed slowly and

consistently over the years.consistently over the years. Punctuated equilibrium says that organisms change in spurts says that organisms change in spurts

followed by long periods of no change at all.followed by long periods of no change at all.

0

50

100

100 MYA 75 MYA 50 MYA 25 MYA

Gradualism

Punctuated Eq.

Regardless of whether it happen it Regardless of whether it happen it happened smoothly or in rapid periods of happened smoothly or in rapid periods of change, organisms try to survive in their change, organisms try to survive in their environment. environment.

Two examples are this are divergent Two examples are this are divergent evolution and convergent evolution.evolution and convergent evolution.

How does speciation happen?How does speciation happen?

Divergent EvolutionDivergent Evolution

All organisms adapt to All organisms adapt to their environment. If there their environment. If there is a particular niche (or is a particular niche (or role) that they fit into, the role) that they fit into, the organism could develop organism could develop an adaptation that would an adaptation that would help them survive. This help them survive. This type of evolution is called type of evolution is called divergent evolution. The divergent evolution. The animals start with a animals start with a similar ancestor and similar ancestor and separate from it. separate from it.

Convergent evolutionConvergent evolution Why do most birds fly?

To get from one place to another. For safety reasons. Etc. What about insects?

Same thing. Then why isn’t a mosquito a relative of a bird.

Because they have evolved convergently.

Convergent evolution is when two different organisms Convergent evolution is when two different organisms develop a similar characteristic to perform the same develop a similar characteristic to perform the same function even though they don’t have a common function even though they don’t have a common ancestor. You have seen this before in analogous ancestor. You have seen this before in analogous structures. Birds and flying insects have a common structures. Birds and flying insects have a common characteristic because it aids in their survival, not characteristic because it aids in their survival, not because they both have bones in their wings.because they both have bones in their wings.

SpeciationSpeciationHow does all How does all

of this work of this work again?again?

Watch the Watch the video to video to review!review!

Well that sounds stupid, thanks Well that sounds stupid, thanks for wasting my time!for wasting my time!

Not Not completely!!completely!!

This really This really does concern does concern you!you!

Watch this Watch this and see!and see!

So if evolution can make anything, So if evolution can make anything, couldn’t we learn to fly one day?couldn’t we learn to fly one day?

Whoa!!!Whoa!!! Not so fast!Not so fast! An adaptation An adaptation

like that would like that would take billions of take billions of years and years and probably millions probably millions of adaptations to of adaptations to get there.get there.