Biology
Evolution by Natural Selection
Evolution by natural selection is the process by which species change over generations. It requires three things: variation (individuals differ), inheritance (offspring resemble parents), and differential survival/reproduction (some variants leave more offspring). Over many generations, populations shift toward variants that best survive and reproduce.
How to Approach Evolution by Natural Selection
Variation arises
Mutations during DNA replication, plus recombination during sexual reproduction, generate genetic variation among individuals. Some variants are neutral, some harmful, some advantageous.
Selection pressure acts
The environment 'tests' each individual: predators, food scarcity, mates, climate. Individuals with advantageous traits survive and reproduce at higher rates than those without. 'Fitness' is reproductive success, not strength.
Population shifts over generations
Because advantageous traits are heritable, the next generation has more individuals with those traits. Repeat over millions of generations: the population accumulates adaptations. Geographic isolation eventually creates new species.
Frequently Asked Questions
What's the difference between evolution and natural selection?+
Evolution is the observed change in populations over time (the fact). Natural selection is one mechanism (the leading theory) that drives it. Other mechanisms include genetic drift, gene flow, and mutation.
Why isn't natural selection 'survival of the fittest'?+
It's actually 'differential reproduction.' An organism that survives but doesn't reproduce contributes nothing to the next generation. 'Fitness' specifically means reproductive success, not physical strength or survival per se.
Does evolution have a direction?+
No. Evolution doesn't aim at complexity or 'progress' — it's response to environment. A successful parasite can evolve to be simpler than its ancestor. Species also go extinct when conditions change faster than they can adapt.
Related Topics
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