Transcript PowerPoint
Speciation “Is that how organisms become special, Ms. Bass?” “Whatever!” Review of Natural Selection You’ve already learned about adaptations. Let’s review by giving these some names. Common Ancestor In other words, organisms that look alike may have had a shared, or common, ancestor in their past. Darwin thought that the finches started with one type of beak that adapted to help them eat the food source on that island. Here are some examples: Nature has three basic ways of choosing what is a useful adaptation. Directional Selection is when nature chooses one adaptation over another one. For example, which squirrel would stand out in the forest? Nature would choose the brown one because it can hide easier. Eventually, enough multicolored squirrels would be killed and it would no longer be in the gene pool. Nature has three basic ways of choosing what is a useful adaptation. Disruptive selection is when nature chooses two extreme variations of a trait over one that is in between them. In this case, the middle size goes away. Sammy Seal says the big one fights too much so he lives. Sammy Seal says the small one is too hard to open so he can live. 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 what is a useful adaptation. Stabilizing selection is when organisms are chosen for being an average size. In this case, the middle size stays. Just right Too small Too big So then how are species “made”? Speciation is the process that organisms take to become a new species. Remember that a species is a group of interbreeding organisms. There are two basic reasons why species would grow apart. Let’s look at them. + If you can’t breed and make babies, or if you don’t have the same process you probably aren’t in the same species. Evolution of Species Geographic isolation When species are separated by a physical barrier, it becomes hard to breed. Eventually, the organisms adapt to the ones around them and the organisms on the other side of the barrier become foreign and form their own gene pool. This may cause the two to no longer be able to breed together. Evolution of Species Reproductive Isolation When mating seasons or structures change, it interferes with how organisms reproduce. If fertile seasons are different, the organisms could evolve into two different species because they will never have a chance to mate or share the same gene pool. If the reproductive structures aren’t compatible, the two organisms can no longer reproduce together. + = ? How does speciation happen? There are two theories that discuss how species develop over time: Gradualism says that organisms have changed slowly and consistently over the years. Punctuated equilibrium says that organisms change in spurts followed by long periods of no change at all. 100 Gradualism Punctuated Eq. 50 0 100 MYA 75 MYA 50 MYA 25 MYA How does speciation happen? Regardless of whether it happen it happened smoothly or in rapid periods of change, organisms try to survive in their environment. Two examples are this are divergent evolution and convergent evolution. Divergent Evolution All organisms adapt to their environment. If there is a particular niche (or role) that they fit into, the organism could develop an adaptation that would help them survive. This type of evolution is called divergent evolution. The animals start with a similar ancestor and separate from it. Convergent 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 develop a similar characteristic to perform the same function even though they don’t have a common ancestor. You have seen this before in analogous structures. Birds and flying insects have a common characteristic because it aids in their survival, not because they both have bones in their wings. Speciation How does all of this work again? Watch the video to review! Well that sounds stupid, thanks for wasting my time! Not completely!! This really does concern you! Watch this and see! So if evolution can make anything, couldn’t we learn to fly one day? Whoa!!! Not so fast! An adaptation like that would take billions of years and probably millions of adaptations to get there.