I would hazard a guess that itās a bit of both. For all populations, long term evolutionary pathways begin with selection of standing variation in the initial population. There could have been populations that were on the boundary of savanna and jungle so that selection could have favored populations that began to venture outside of their previous range. Subsequent changes could have increased fitness in this environment.
Judging by what little I know of human evolution, the wide and squat human pelvis appeared to evolve much earlier than other adaptations. For example, we see a very human like pelvis in Ardipithecus, but very ape like features elsewhere.
I suspect itās a bit like the rock pocket mice above. Could there have been a few black mice out there in the light colored desert that were able to immediately take advantage of the black basalt as soon as it appeared? Perhaps. It is also possible that the black phenotype emerged after the black basalt island was already there. If the black phenotype had never emerged you would still have the light colored phenotype in the light colored desert.
I still remember trying to get that across to a NASA guy who insisted that no humans could have genes making it just fine to live in 38% Earth gravity; his argument was that until people have lived in some situation they canāt have mutations making them fit to do so.
I suspect this error comes from misunderstanding the meaning of āadaptationā.
While I am not in a position to provide a detailed response to the study you referred, I form a strong impression that the mice studied have the inbuilt mechanisms that produce the colours. From the paper:
"Whereas Mc1r darkening mutations have been identified in other species (16, 21ā25), the ecological context for the changes either is not understood (24, 25) or is due to artificial selection (22, 23). Owls are important predators of pocket mice (8, 9) and are known to discriminate between light and dark mice on light and dark substrates even when foraging at night under low light intensity (10). Thus, it is likely that owls play an important role in selecting for concealing coloration. The data reported here present a rare example of the molecular changes underlying adaptation in a simple and natural ecological setting."
It is clear that this does not address my point, in that random mutations occur while random environmental/ecological changes also happen.
Iām not sure what you mean by āinbuilt mechanismā. It required at least one mutation to get the black phenotype, assuming ancestors were light colored. āInbuiltā to me means either phenotype could be produced in the same genetic background, but you may have a different definition.
The leap to ātherefore selection is impossibleā is what I donāt see support for. All you need is enough environmental stability over a long enough period of time for those environmental conditions to change the allele frequencies within a population. Just as another example, taking an oral antibiotic will produce selective pressures and changes in both the species distribution of bacteria in your gut and the genetics of those species that stick around. The correlation of human skin color and latitude is another example of selective pressures for UV protection and vitamin D production. The geographic correlation between the sickle cell trait in humans and endemic malaria is another classic example:
If selection is impossible, why do we see it all throughout nature?
Lamarckism is very intuitive, even if it ends up being wrong. I donāt blame non-scientists for these types of misunderstanding, unless they decide to lecture all biologists on how they are wrong about everything.
My Dad once asked me how 23andme and other similar services worked. I tried to explain the implications of mitochondrial, y-chromosomal, and autosomal DNA sequencing and I wasnāt able to make any headway, at least in the short amount of time we had. Even the concept of diploidy was difficult to explain in a way that he comprehended (again, in a quick 3 minute explanation). Biology, and genetics in particular, isnāt well understood by the random Joe/Jane on the street. It reminds me of the time my organic chemistry lab TA felt frustrated when I was constantly moving protons between atoms instead of electrons. He must have felt the same way I did trying to explain DNA sequencing.
I get the feeling we are not discussing the same thing. I maintain that variation is ubiquitous but do not support the overall theory of random evolution with the version of natural selection. Inbuilt mechsnism(s) mean just that, in that changes at the molecular level are in the final analysis subject to the laws of chemistry, albeit for very complicated sytems.
Maybe @T_aquaticus means to say that natural selection adapts a population to the prevailing environment at the time. If the change in environment is directional, the phenotypic change in organisms as a result of N.S. will also be directional. e.g., a blacker substrate will result in blacker coat colour in miceāa directional change in the āblacknessā of fur. If the environment is stable, we expect stabalizing selection (the average phenotype is selected) resulting in no phenotypic shift. However, one could hypothetically say that the soot-covered black rocks somehow get clean again, such that the direction of selection is back to white fur in mice.
Over time, one would see an evolutionary pattern of mice becoming blacker, and then āreversingā to become whiter again. A long term perspective would show that evolutionary change did not result in a permanent shift of phenotypes in a continual direction (evolutionary theory does not entail that populations must move in a continual, predictable direction).
But these phenotypic changes are not ārandomā. They are specifically those changes that adapt a population to the prevailing environment at the time.
Umm . . . No. Where did I say anything about a read only genome?
I agree that it is important to note that Crick was talking about sequence information, and that it canāt move from protein to protein or from protein to nucleotide sequence. In this instance, sequence information is the order of nucleotide bases in DNA/RNA or the order of amino acids in proteins. In other words, there is no biological process that uses the amino acid sequence of a protein as a template for creating a string of nucleotide bases or to construct a string of amino acids.
Crick called it the Central Dogma because it was the most basic understanding that molecular biologists were working from at the time. It is worth noting that Crick was instrumental in discovering the role of transfer RNA in protein translation.
I would strongly advise reading Crickās 1970 paper on the Central Dogma where he confronts the misunderstandings that existed more than 50 years ago, and seem to persist to this day.
Is there a different procedure for copying a non-write protected SD card? I donāt understand what difference the write protection plays in this context.
I would also argue that any similarity between copying DNA and copying digital media is very surface level. There isnāt much in the way of specific similarities.
Both mutations and abiotic environmental changes happen randomly with respect to each other. Organisms without advanced biotech abilities canāt say āI think it would be useful to mutate these bases to gain this ability.ā The environment doesnāt change to fit particular mutations (although mutations change the characteristics of neighboring organisms and thus affect the environment. )
But mutations and environmental changes are both constrained by laws of nature, existing structures, etc. Likewise, a coin toss can be considered random because we canāt predict heads versus tails, but we can be rather confident that the coin toss will produce one of those two options and not flying green elephants with wings oh so blue.
Both mutations and environments generally make many small changes rather than sudden big ones. The tendency of humans to make sudden big changes in the environment is one reason why we are so good at wiping out other species.
The peppered moth example has the advantage that we do have some before and after data. Extra-dark individuals occurred rarely in the population. As pollution made more tree trunks dark, the dark forms became more successful. Improved environmental regulations led to a decrease in dark tree trunks and a corresponding decrease in dark moths. The mutations were random in the sense that the moths couldnāt decide to mutate and couldnāt anticipate the need. They were non-random in that they reflected the exising genetic makeup of the moths and the probability of mutations for the exact gene region.
The issue I see is whether information can pass from the organism to the genome. I see Noble saying this can happen in a limited number of verifiable circumstances.
That hinges on what you mean by passing information to the genome.
Does the insertion of a retrovirus into the host genome count? If an environmental stressor activates a transposon that then randomly inserts itself into the genome, does that count? What about methylation of DNA in response to the environment? All of these mechanisms, and more, are already included in the modern theory of evolution.
What doesnāt happen is sequence information being transferred from an amino acid sequence to a nucleotide sequence.
I want to continue on this subject, but I am wondering right now if you saw the definition I shared of āphysiological functionā, the term Noble used, and if you can see how that is synonymous with āfitnessā.
