Evolution: the idea that one species changes into another over time

Natural Selection: Darwin’s suggestion for the process by which evolution might occur

Evolution by Natural Selection (Darwinian Evolution)

1. There is variation in a species

2. More individuals are born than the environment can sustain, so some individuals must die.

3. The individuals that survive tend to be those that have alleles which give them a selective advantage in their environment (i.e. they are the best adapted to their environment, e.g. camouflaged). These are the “fittest”

4. The fittest survive long enough to reproduce and pass their alleles onto the next generation.

5. Over a few generations the frequency of “fit” alleles increases and the frequency of “unfit” alleles decreases

6. Soon all / most individuals have the “fit” phenotype and the “unfit” phenotype is eradicated

7. This process continues over many generations

8. Over this time new mutations occur, which give new even better alleles

9. Over time the mutations accumulate in the phenotype until the organism is unable to reproduce (i.e. produce fertile offspring) with the original organisms. At this point a new species has been produced (speciation)

This process is speeded up by isolation (see 4.5.14) because this stops the influx of alleles from outside and allows new mutations to accumulate in the genotype more quickly.