*remained or spread because they /survived/. This is not exactly chance. The original genetic mutations are chance, the ones that stick around are not.evolved by accident, and remained or spread by chance.
Interestingly, there is emerging evidence in epigenetics that non-DNA changes can also lead to heritable traits. So perhaps Lamarck wasn't all wrong. Grabbing the link, I just learned of paramutation, which is weird. It seems it's going to become even more difficult to speak properly about evolution. :/
Yeah, TBH I don't think I understand paramutation enough to explain it, even after reading this a couple of times. I wonder if paramutations themselves might be activated or inactivated by environmental factors. For example, perhaps in times of environmental stress paramutation can be enhanced, leading to more phenotypic variability, and thus, more possibilities to find a more advantageous phenotype. I have to think that dogs have to have some of this going on. I recall reading a study that it only takes a few generations of selective breeding to turn a wild canine into a very different-looking domestic dog.Interestingly, paramutation can result in a single allele of a gene controlling a spectrum of phenotypes. At r1 in maize, for example, the weaker expression state adopted by a paramutant allele can range from completely colorless to nearly fully colored kernels. This is an exception to the general observation that traits that vary along a continuum are usually controlled by multiple genes.
True enough -- but it's also true that we can't claim to know what everything in our body does and why. Eye color, obviously, is not going to turn out to have some amazing significance, but a different example might. Also, I'm interested in knowing if varying eye color is strictly a mutation or not, and if so how the various colors came about. Raises some questions for me.
People with lighter eyes tend to have more sensitivity to light. Couldn't there be a biological advantage to having darker eyes?
Perhaps not the best source but then, I'm about to watch a movie and am short on time.
Not always. There can easily be two or more genetic variants that have more or less even odds of survival, but one happens to be dominant, say, in a valley that gets flooded, thus ending their lifespan. The one that's left over then gets to acquire this niche when the flooding subsides. Chance is a very key player in evolution, not just w.r.t. gene mutation.