Rabbits!  An Example ofHow Evolution Works              Emily Gaydos, 4-10-12
Once upon a time, there were rabbits in a desert. They    were very happy and bred like… well, rabbits.
There was variation in the population—some rabbits were darker, some were           lighter. It didn’t matter, though—they...
But then, hawks discovered the rabbits and the hunt was on!
On one side of the desert, the sand was lighter in color, and that made it    easier for the hawks to see and catch dark o...
On the other side, the sand was darker, and that made it easier for the hawks                 to see and catch light or ve...
Because of the selection pressure of hawk predation, the frequency of traits in                 the population of rabbits ...
On the side with lighter soil, the dark and very light rabbits disappeared—eaten by the hawks. On the other side, the ligh...
Since rabbits tend to breed with nearby rabbits, most of the light-coloredrabbits bred with other light-colored rabbits an...
On the other side, the dark-colored rabbits bred with other dark-coloredrabbits and had mostly dark-colored offspring. The...
Thus, over time, the rabbits began to look like two different populations—onewith a higher frequency of the trait/genes fo...
Since the selection pressure was maintained by Hawk Predation, genes for      Dark Coats were pretty much wiped out in rab...
And then one year, a mighty rain cut a new flood channel in the       desert, separating the rabbits from each other!
Since they could no longer mingle and exchange DNA, the separated  populations of rabbits became more and more unlike each...
??                                           ??Over time, they became so different genetically that they couldn’t interbre...
Evolution is the change of trait/gene frequencies in a population over time.
Natural selection happens when something about the environment—like soil   color or predation—makes an animal’s traits eit...
If an animal’s traits are a better fit to the environment and therefore result in    more offspring, the number of critter...
If an animal’s traits are a worse fit to the environment and therefore result in    less offspring, the number of critters...
Selection pressures can be complex, leading to complex adaptations. Let’s saycoyotes also move in. Now, faster, skinnier r...
…while on the other side, the sandier soil makes it easy to dig burrows, and smaller, fatter rabbits with a tendency to bu...
The difference in fitness between competing animals doesn’t have to be big to  matter. If a trait gives a critter even a s...
Over time, even these slight adaptations can add up as the trait/gene frequencies       are pushed in different directions...
The relationship between animals and the selection pressures of their environments can be outrageously complex. All creatu...
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Rabbits an example of evolution 1

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The relationship between animals and the selection pressures of their environments can be outrageously complex. All creatures on the planet today are the result of millions and millions of years of these interactions—generation after generation of natural selection for traits/genes just a little bit more fit for each population’s unique and changing environment. Yet, for each species and each adaptation, the underlying mechanism is the same:

In response to selection pressure, the frequency of traits and the genes controlling those traits changes in a population over time. That’s evolution.

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Rabbits an example of evolution 1

  1. 1. Rabbits! An Example ofHow Evolution Works Emily Gaydos, 4-10-12
  2. 2. Once upon a time, there were rabbits in a desert. They were very happy and bred like… well, rabbits.
  3. 3. There was variation in the population—some rabbits were darker, some were lighter. It didn’t matter, though—they were all happy.
  4. 4. But then, hawks discovered the rabbits and the hunt was on!
  5. 5. On one side of the desert, the sand was lighter in color, and that made it easier for the hawks to see and catch dark or very light rabbits.
  6. 6. On the other side, the sand was darker, and that made it easier for the hawks to see and catch light or very dark rabbits.
  7. 7. Because of the selection pressure of hawk predation, the frequency of traits in the population of rabbits began to change.
  8. 8. On the side with lighter soil, the dark and very light rabbits disappeared—eaten by the hawks. On the other side, the light and very dark rabbits were eaten first. Over time, only the best camouflaged rabbits remained.
  9. 9. Since rabbits tend to breed with nearby rabbits, most of the light-coloredrabbits bred with other light-colored rabbits and had light-colored offspring. The bunnies born without good camouflage were quickly eaten up.
  10. 10. On the other side, the dark-colored rabbits bred with other dark-coloredrabbits and had mostly dark-colored offspring. The bunnies born without good camouflage there were also quickly eaten up.
  11. 11. Thus, over time, the rabbits began to look like two different populations—onewith a higher frequency of the trait/genes for lighter coats and the other with a higher frequency of the trait/gene for darker coats.
  12. 12. Since the selection pressure was maintained by Hawk Predation, genes for Dark Coats were pretty much wiped out in rabbit population on lightsoil, while genes for Light Coats dwindled in the population living on dark soil.
  13. 13. And then one year, a mighty rain cut a new flood channel in the desert, separating the rabbits from each other!
  14. 14. Since they could no longer mingle and exchange DNA, the separated populations of rabbits became more and more unlike each other.
  15. 15. ?? ??Over time, they became so different genetically that they couldn’t interbreed when they did meet again. The frequency of traits/genes had changed so dramatically that the rabbits had become two distinct species!
  16. 16. Evolution is the change of trait/gene frequencies in a population over time.
  17. 17. Natural selection happens when something about the environment—like soil color or predation—makes an animal’s traits either more fit or less fit (advantageous) in that given environment.
  18. 18. If an animal’s traits are a better fit to the environment and therefore result in more offspring, the number of critters having those traits will increase.
  19. 19. If an animal’s traits are a worse fit to the environment and therefore result in less offspring, the number of critters having those traits will decrease.
  20. 20. Selection pressures can be complex, leading to complex adaptations. Let’s saycoyotes also move in. Now, faster, skinnier rabbits might have a better chance at surviving to have more offspring with their faster, skinnier genes…
  21. 21. …while on the other side, the sandier soil makes it easy to dig burrows, and smaller, fatter rabbits with a tendency to burrow have a better chance at surviving to breed more small, fat burrowing rabbits…
  22. 22. The difference in fitness between competing animals doesn’t have to be big to matter. If a trait gives a critter even a slight advantage that results in a few moreoffspring, there will be slightly more of those advantageous genes in the population.
  23. 23. Over time, even these slight adaptations can add up as the trait/gene frequencies are pushed in different directions in response to selection pressure.
  24. 24. The relationship between animals and the selection pressures of their environments can be outrageously complex. All creatures on the planet today are the result of millions and millions of years of these interactions—generation after generation ofnatural selection for traits/genes just a little bit more fit for each population’s unique and changing environment. Yet, for each species and each adaptation, the underlying mechanism is the same: In response to selection pressure, the frequency of traits and the genes controlling those traits changes in a population over time. That’s evolution. Emily Gaydos, 4-10-12
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