The course of evolution is steered by selection pressure. For example, giraffes with the longest necks can reach more food, so the "long neck" trait is favored in reproduction. Over large time scales, DNA mutations may develop that further increase fitness. For example, consider a hypothetical mutation in the giraffe's upper vertebrate that enables even longer necks than could be structurally supported prior to the mutation.
My question is this: is this mutation completely random, or could the lifestyle of the giraffe tip the odds towards neck mutations? Perhaps the constant use of the neck muscles stimulates expression of the "long neck" genes (or maybe some other epigenetic process is at work), and this somehow makes future neck vertebrate mutations more likely than, say, kneecap mutations?
I have been thinking about this for a long time. I believe the answer is yes, but I would need some time to find whether one can make that case from current research. If you are interested in a more detailed argument, let me know, I will look into it.
Thanks Juliette, certainly am interested in learning more... even just a paper or a discussion to put me on the right direction.
I presume the prevailing response will be that mutations are simply random, and ones that re-enforce fitness are selected. These are the only ones that we see; we don't see the myriad of random mutations that were rejected. Yet, even on evolutionary time scales, it feels almost too convenient that animals mutate in ways that serve their needs. Perhaps this says more about my inability to comprehend evolutionary scales than anything...
Dear Adam,
I think this is an open and consistently interesting question. "Soft inheritance" happens when variations resulting from environmental conditions are passed on to the next generation (def from Mayr). This process exists and has been observed to produce interesting effects. A classic example of this comes from the licking and grooming in rats, which shows that the intensity of this behavior, experienced by a pup, can be epigenetically inherited from the mother’s behavior and maintained for some generations. However, as you explained, this process is not commonly observed and the rule of random mutations followed by selection remains the main process.Obviously the are many traits that we cannot directly observe and probably at cell level this process is more important than for higher level of integration.The old paradigm does not fail in finding an explanation; in fact epigenetic processes might rely on mechanisms that are themself genetically inherited.
Thanks Hannan- I'd never heard the term "Lamarkian". From Wiki's epigentic Lmarkian seciton: seems like certain traits can indeed be inherited epigenetically, but there's no reason to think that they get imprinted into the genome.
"A 2013 study published in Nature Neuroscience reported that mice trained to fear the smell of a chemical called acetophenone passed their fear onto at least two generations.[119][120] The science magazine New Scientist commented on the study saying, "While it needs to be corroborated, this finding seems consistent with Lamarckian inheritance. It is, however, based on epigenetics: changes that tweak the action of genes, not the genes themselves. So it fits with natural selection – and may yet give Lamarck's name a sheen of respectability."
Perhaps we'll find in the future that indeed epigenetic factors can affect mutation rates/direction, but there's probably no evidence for that yet.
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