Evolutionary Thought

Evolutionary Thought #

pre-darwin: transmutation of species occurred, but no hypothesis of mechanism
- Oswald Avery, Crick + Watson: 1940s discovery of DNA

Consequence: offspring w/ favorable traits have more offspring, ⇒ adaptation by natural selection

5-year voyage on Beagle as naturalist
Galapagos islands:
- founder effect: evolution depends on small group of species who happened to arrive. first arrivers = little competition ⇒ more
- adaptive radiation: diversification
  - Syms Covington unto locations, John Gould realized all collected
  - each finch had a different beak to specialize in food types

during drought, food is scarce and only food is hard seeds
finches begin to adapt to have larger beaks
- those that already have big beaks more successful
decrease in variation in size

Success is local and temporary; environments are constantly changing.

bush structure: current adaptations built off of historical traits, but are not always getting “better”

This also applies to cultural evolution: culture is a response to the present environment, and must build off past cultures

2 problems:

makes them more vulnerable to predators
Solution: sexual selection — competition to reproduce, need to compete within a species
- can lead to lower survivability, higher reproductivity
handicap principle: expensive traits that demonstrate fitness
- example: peacock feathers, deer antlers, widowbird tails (longer = better)
- only the smartest, most fit individuals can survive predators w/ handicap
- typically honest indicators (no way to cheat), eg barn swallows who have lower parasite load have longer tails
Sexual selection has same goal as natural selection (increase offspring), but different process
- intrasexual: compete against same sex
- intersexual: attract opposite sex