Skills 4 - 7: Types of evolution
Convergent evolution
Convergent evolution
Skill 4:
Skill 4:
a) How are convergent and divergent evolution different?
a) How are convergent and divergent evolution different?
b) Which species are more closely related, those from convergent or divergent evolution?
b) Which species are more closely related, those from convergent or divergent evolution?
Convergent evolution is the process by which unrelated species evolve similar physical characteristics because they have the same environmental pressures.
Convergent evolution is the process by which unrelated species evolve similar physical characteristics because they have the same environmental pressures.
'Converge' means to come together.
'Converge' means to come together.
"Diverge" means to move apart.
"Diverge" means to move apart.
Divergent evolution is the process by which a species evolves into two different species. Each group is subject to different environmental pressures which select for different survival advantages. What environmental conditions could have caused the species on the left to become larger and darker while the species on the right became smaller and lighter?
Divergent evolution is the process by which a species evolves into two different species. Each group is subject to different environmental pressures which select for different survival advantages. What environmental conditions could have caused the species on the left to become larger and darker while the species on the right became smaller and lighter?
Speciation
Speciation
Skill 5: Explain speciation, or the formation of new species from one original species.
Skill 5: Explain speciation, or the formation of new species from one original species.
These are finches, a type of bird that Darwin observed on many of the Galapagos islands. He noticed that they all appeared to be finches, yet the birds on each island had distinct differences from those on other islands, such as their beak size and structure. He proposed that different environments on the various islands applied different selective pressures. For example, a thick beak might be good on an island with a lot of seeds, while a thinner beak would be better for getting nectar from flowers.
These are finches, a type of bird that Darwin observed on many of the Galapagos islands. He noticed that they all appeared to be finches, yet the birds on each island had distinct differences from those on other islands, such as their beak size and structure. He proposed that different environments on the various islands applied different selective pressures. For example, a thick beak might be good on an island with a lot of seeds, while a thinner beak would be better for getting nectar from flowers.
There are several types of isolation that can lead to new species.
There are several types of isolation that can lead to new species.
Geographic isolation
Geographic isolation
If two groups of the same species are separated by the geography of the area, the different environmental pressures can cause changes between the two groups and eventually lead to the groups becoming different species. They do not mix or mate because the geography of the area keeps them physically separated.
If two groups of the same species are separated by the geography of the area, the different environmental pressures can cause changes between the two groups and eventually lead to the groups becoming different species. They do not mix or mate because the geography of the area keeps them physically separated.
Behavioral isolation
Behavioral isolation
Since these two groups of Meadowlarks find mates by singing a certain song and each group's song is different, they will not mate with each other. This is a behavior that prevents the groups from mixing or mating. They are isolated from each other by their behavior.
Since these two groups of Meadowlarks find mates by singing a certain song and each group's song is different, they will not mate with each other. This is a behavior that prevents the groups from mixing or mating. They are isolated from each other by their behavior.
Temporal (time)
Temporal (time)
If species do not reproduce at the same time, they will not mix or mate with each other. For example, I have early blooming and late blooming apple trees in my yard. When the early bloomers have flowers and are starting to form apples, the others are not reproducing yet. When the late bloomers have flowers and are reproducing, the early bloomers have already finished. This temporal isolation keeps my apple trees from cross pollinating each other.
If species do not reproduce at the same time, they will not mix or mate with each other. For example, I have early blooming and late blooming apple trees in my yard. When the early bloomers have flowers and are starting to form apples, the others are not reproducing yet. When the late bloomers have flowers and are reproducing, the early bloomers have already finished. This temporal isolation keeps my apple trees from cross pollinating each other.
Gradualism and punctuated equilibrium
Gradualism and punctuated equilibrium
Skill 6: Explain why evolution is sometimes gradual and sometimes punctuated.
Skill 6: Explain why evolution is sometimes gradual and sometimes punctuated.
In an evolutionary timeframe, sometimes changes accumulate in a species "quickly" and sometimes it is very gradual.
In an evolutionary timeframe, sometimes changes accumulate in a species "quickly" and sometimes it is very gradual.
Due to gradual changes in the horse's environment, small changes accumulated over a very long period of time. This type of evolution is called "gradualism" as it happens gradually.
Due to gradual changes in the horse's environment, small changes accumulated over a very long period of time. This type of evolution is called "gradualism" as it happens gradually.
At other times, there are sudden changes in a species' environment, leading to rapid change in a species who survive the change. This could be the result of a natural disaster such as a volcanic eruption, asteroid impact with earth, or ice age. In these scenarios, many organisms will die off, but some individuals will have a survival advantage and repopulate the area. The new individuals are significantly different than the original 'norm' or else they wouldn't have survived the event. Since many individuals died, there are extra resources for those who survived to reproduce and repopulate quickly.
At other times, there are sudden changes in a species' environment, leading to rapid change in a species who survive the change. This could be the result of a natural disaster such as a volcanic eruption, asteroid impact with earth, or ice age. In these scenarios, many organisms will die off, but some individuals will have a survival advantage and repopulate the area. The new individuals are significantly different than the original 'norm' or else they wouldn't have survived the event. Since many individuals died, there are extra resources for those who survived to reproduce and repopulate quickly.
The cartoon above is just for fun!
The cartoon above is just for fun!
Fossil record
Fossil record
Skill 7: Explain how examination of the fossil record supports the theory of evolution.
Skill 7: Explain how examination of the fossil record supports the theory of evolution.
When an organism dies, if it is not decomposed, but covered by soil, it can become a fossil. The fossil record shows us what lived in a certain area at a particular time. Notice how the type of environment changed over time. It was first a lake and later, dry land.
When an organism dies, if it is not decomposed, but covered by soil, it can become a fossil. The fossil record shows us what lived in a certain area at a particular time. Notice how the type of environment changed over time. It was first a lake and later, dry land.
The older fossils are found deeper in the ground. That makes sense, because they were covered in dirt and then something else lived above them.
The older fossils are found deeper in the ground. That makes sense, because they were covered in dirt and then something else lived above them.
Sideling Hill
Sideling Hill
Near Hancock, Maryland
Near Hancock, Maryland
As you can see in the picture to the left, the strata, or layers of rock, are very obvious. Sometimes, they are not flat which can make it harder to tell which layers are older. Do you know how geologists can date fossils to see how old they are?
As you can see in the picture to the left, the strata, or layers of rock, are very obvious. Sometimes, they are not flat which can make it harder to tell which layers are older. Do you know how geologists can date fossils to see how old they are?
*Class activity - half-life demonstration using pennies and removing 'tails.'
*Class activity - half-life demonstration using pennies and removing 'tails.'
*Guest herpetologist - Rattlesnake demonstration to show how instincts evolve
*Guest herpetologist - Rattlesnake demonstration to show how instincts evolve
Those who come in with their work finished can watch, "Cosmos - Some of the Things That Molecules Do."
Those who come in with their work finished can watch, "Cosmos - Some of the Things That Molecules Do."