What Evolution NeedsPosted: March 24, 2009
Evolution needs six essential properties for the process to start and continue. Understand that these six points come from pages 104-5 of How Brains Think by William H. calvin.
- It involves a pattern. Classically, this is the string of DNA bases called a gene. As Richard Dawkins pointed out in The Selfish Gene, the pattern could also be a cultural one such as a melody, and he usefully coined the term meme for such patterns. the pattern could also be the brain activity patterns associated with thinking a thought.
- Copies are somehow made of this pattern. Cells divide. People hum or whistle a tune they’ve overheard. Indeed, the unit pattern (that’s the meme) is defined by what’s semi-reliably copied–for example, the gene’s DNA sequence is semi-reliably copied during meiosis, whereas whole chromosomes or organisms are not reliably copied at all.
- Patterns occasionally change. Point mutations from cosmic rays may be the best-known alterations, but far more common are copying errors and (as in meiosis) shuffling the deck.
- Copying competitions occur for occupation of a limited environmental space. For example, several variant patterns called bluegrass and crabgrass compete for my backyard.
- the relative success of the variants is influenced by a multifaceted environment. For grass, the operative factors are nutrients, water, sunshine, and how often the grass is cut, and so on. We sometimes say that the environment “selects,” or that there is selective reproduction or selective survival. Charles Darwin called this biasing by the term natural selection.
- The next generation is based on which variants survive to reproductive age and successfully find mates. The high mortality among juveniles makes their environment much more important that that of adults. This means that the surviving variants place their own reproductive bets from a shifted base, not from where the center of the variations was a conception (this is what Darwin called the inheritance principle). In this next generation, a spread around the currently successful is again created. Many new variants will be worse than the parental average, but some may be even better “fitted” to the environment’s collection of features.