Back To CourseHolt McDougal Biology: Online Textbook Help
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Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.
Evolution is the process where organisms change over time. Of course, when you think of evolution, images of fish growing legs and walking on land may come to mind. But evolution is a slow process, taking thousands or even millions of years, so fish don't suddenly sprout legs and walk out of the water.
In this lesson, we are going to explore divergent and convergent evolution so you can have a better idea of why organisms look the way they do! Both of these types of evolution are going to be impacted by environmental selective pressures. In other words, those organisms best suited to an environment will be able to survive and reproduce, passing on their genes as they do so. Organisms that are not well-suited will die off, as will their genes.
It's also important to remember that a population must have a lot of variety in order for this to happen. For example, consider variation in humans: some are tall, some are short, some have red hair, some have black hair, some are light-skinned, and others are dark-skinned. Like humans, other organisms have a lot of variation within a population.
We are going to follow a group of imaginary critters, which we'll call the Blumps, through the process of divergent evolution to help us understand it. Divergent evolution is the process whereby members of a species become more and more different, eventually resulting in two (or more) new species. In other words, the Blumps will 'diverge,' thus creating a new species. Remember, like humans, the Blumps have a lot of variation: some are large and some are small, and some are darker and some are lighter.
One spring, a flood disrupts the Blumps' environment, causing the population to be divided. On one side of the water it's marshy, and on the other side it's mountainous. The population remains divided for millions of years, and each new environment has unique selective pressures.
For example, the marshy side suits light, small Blumps that can blend in with the grasses and sneak up on prey (and hide from predators). The mountainous side favors Blumps that are large and dark. The darker, larger Blumps blend in with the landscape and are able to navigate the large mountainous peaks. Because the Blumps that are best suited for each environment survive and reproduce, over time the marshy side has predominantly light, small Blumps and the mountainous side has predominantly dark, large Blumps. Over hundreds of generations, the two populations of Blumps become more and more different and eventually become two separate species. And, viola, you have divergent evolution!
Adaptive radiation is a type of divergent evolution where a group of organisms quickly diverges into new species. Now, when you hear the word 'quickly' you might think of only a few days, but 'quickly' in evolutionary terms is much longer - like 500,000 years or more. So keep that in mind, and realize these things don't happen overnight! This process gets the name 'radiation' because new species radiate from a common ancestor. This tends to occur when organisms move into a new environment with a lot of available opportunities.
To help us understand this, let's talk about a real-life example. On the Galapagos Islands, there are many species of finch. When Charles Darwin visited the Galapagos, he noted that the islands' finches looked a lot alike, yet some had key differences like the size and shape of their beaks. As the population of finches encountered each new island, those best suited to eat the food on that island would survive and reproduce. The common ancestor of the finches underwent adaptive radiation, with several new species developing. For example, on one island where seeds were plentiful, the finches that had the beaks best suited for seed eating survived and reproduced. On another island, the finches best suited for insect eating survived and reproduced. In the end, there were many new finch species, each with slightly different beaks.
You've probably noticed that nature is a powerful thing. In our Blumps story, different environments shaped the Blumps into two separate species, and on the Galapagos Islands, different selective pressures resulted in finches with different beaks. However, nature cannot only create new species from a common ancestor, but it can also cause two unrelated species to look alike. Convergent Evolution is just that, when unrelated organisms evolve similar characteristics due to similar environmental pressures. The word 'converge' means to come together, so two unrelated organisms 'come together' to have similarities due to environmental pressures.
Let's examine another made-up scenario to illustrate this idea. Pretend there are two similar environments that both grow a speckled tree. These two environments are thousands of miles apart. In each environment, there are animals that feed on the speckled tree's fruit. The animals that blend in with the speckled tree are better able to survive and reproduce, since predators don't eat them as often. Over time, the animals living in both environments evolve a speckled-colored coat. Even though the two species are unrelated, the selective pressures from the two environments caused them to have a similar coloration.
Now, let's look at some real examples. Sharks and dolphins live in similar environments that select for organisms that can swim well. Sharks and dolphins are not closely related, yet they are similar in color and have a similar body shape. They also live in similar habitats, which has selected for a specific body shape and color.
Another example of convergent evolution is the evolution of flight. Certain environmental pressures favored flight, and those animals that could fly were able to survive and reproduce, thus promoting the species. Flight has evolved separately in birds, bats, and insects. Birds, bats, and insects are not closely related, and their wings have evolved from different structures in each of these groups. Yet, they all have wings because the environments they lived in selected for flight.
Understanding evolution, or how organisms change over time, is the basis for understanding biology. This lesson examined divergent evolution, or how organisms 'diverge' and become separate species. We used the made-up Blumps to illustrate how a flood can isolate a species and how different environmental pressures can cause that species to 'diverge' into two (or more) new species. Then, we looked at the real example of Darwin's finches, which underwent adaptive radiation, or divergent evolution that occurs rapidly and causes a species to 'radiate' into many new species.
Finally, we examined convergent evolution, where unrelated species 'converge' on certain similar characteristics due to environmental pressures. We used the made-up speckled tree environments to illustrate how two unrelated species could develop similar coloring. Real-life examples of convergent evolution include the body shape and color of sharks and dolphins and the different, yet functionally similar, wings of birds, bats, and bees.
Try to set a goal, at the end of the video, to be able to:
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Back To CourseHolt McDougal Biology: Online Textbook Help
34 chapters | 314 lessons