Variation thats important to evolution

You can partition variation by whether it's heritable (or not) or has fitness consequences (or not):

1 Heritable variation: This type of variation is genetic; these are the differences at the DNA level that are passed from parent to offspring.

i Non-heritable variation: This type of variation is the result of the environment factors, things like diet, amount of sunlight, and so on — not genes.

i Variations that have fitness consequences: These variations impact, for better or worse, how well an organism is able to survive and reproduce.

1 Variations that don't have fitness consequences: These variations don't impact either positively or negatively an organism's ability to survive and reproduce.

The type of variation determines in what manner (or even whether) it has an impact on the genetic makeup of future generations:

1 If a variation has a fitness consequences but the variation isn't heritable, it won't lead to evolution. For example, people with really cute tattoos may be more likely to pass along their genes, but there's no genetic component to getting a tattoo. Their genes are, on average, no different from anyone else's genes. Remember: Without heritable variation, there is no evolution (or evolution books, for that matter).

1 If a variation is heritable but it doesn't cause any fitness differences, then the frequencies of these differences in a population will change only as a result of genetic drift, not natural selection.

1 If variation is both heritable and has fitness consequences, well then, evolution by natural selection can occur.

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