Natural Selection
There are three parts of natural selection:
1. There are a variety of traits in a given population due to mutations, sexual reproduction, gene flow, or genetic drift.
2. These different organisms don’t all reproduce the same amount. The ones that r best adapted to survive and reproduce are the ones that leave the most offspring.
3. Traits are passed down from parents, fit enough to reproduce, to their offspring. The offspring then have those better adaptations, which will help them thrive in their environment and reproduce successfully.
So, over a period of time, the traits most suited for a specific environment are passed down more frequently and more organisms in a population will have those traits.
Darwin’s example of natural selection: finches from the Galapagos Islands.
The finches from the mainland migrated to the islands and over time the finches on each island adapted to the specific environment of their island. The change is most apparent in the beaks of the birds that evolved for a specific food source on a specific island. The birds on each island changed because of sexual reproduction and/or mutations and through natural selection the ones that had the best adapted beaks survived and reproduced the most, thus changing the beaks of the entire population over time. (See figure 4)
Sexual Selection:
Sexual selection is a specific kind of natural selection, which is based on how appealing an individual is to the opposite sex. Females choose mates based on their traits so if a male has favorable characteristics the female will choose him and those traits will be passed on to the next generation.
Fitness and Adaptations
The struggle for existence leads to the survival of the fittest or, in other words, those who are “just good enough” to survive. Fitness is a result of adaptations (inherited traits that increase the chance of survival). Adaptations include camouflage, shorter or longer limbs, height, and speed.
Adaptations are present in a species because they provide an improved useful function. The better adapted an organism is, the more successful it is at surviving and reproducing. This way, the “fit” or “good enough” traits are passed down most often. An organism doesn’t necessarily need to be the best adapted in a group to survive. As long as its traits are “just good enough” to allow it to survive and reproduce, its genes will be passed on to the next generation, even if they aren’t the best possible.
