MEPX
Chapter 4 of 10All chapters
  1. 1The mechanism
  2. 2Where variation comes from
  3. 3Selection
  4. 4Chance
  5. 5How species form
  6. 6The evidence
  7. 7Common misunderstandings
  8. 8Deep time
  9. 9Human evolution
  10. 10Why it matters practically

Chapter 4 of 10

Chance

Not everything is an adaptation.

Genetic drift

In small populations, which variants spread is heavily influenced by luck. A useful trait can vanish and a neutral one can take over, purely by chance.

  • Founder effects appear when a small group starts a new population.
  • Bottlenecks after a crash leave lasting marks on diversity.

Beware just-so stories

Not every feature has an adaptive explanation. Some are by-products, some are leftovers, and some are the result of drift, so an explanation needs evidence rather than plausibility.