In this part

£r volution by natural selection requires mutations.

Now, there aren't many times when you hear the word "mutation" and think it's a good thing. Even in evolutionary terms, most mutations are bad. But some mutations give an organism a fitness advantage resulting in its being able to survive and reproduce. The result? More of the genetically advantaged organisms in future populations.

But selection isn't the only evolutionary force. Genetic drift (a fancy way of saying random events) can affect gene frequencies, too. If a mudslide wipes out a large portion of a wildflower that just happens to bloom pink in a particular area, then there will be fewer pink-flowering plants in later generations.

This part tackles the mechanisms of evolutionary change (variation, mutation, selection — both natural and artificial — genetic drift, and so on); their results (loss of genetic variation, change in genetic variation, and specia-tion); and how to retrace past evolutionary events and see the relationships among species (through phylogenetic trees).

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