We have pointed out that many conditions must persist well enough, and long enough for this to be a helpful explanation for complex traits. Not that it is wrong per se but that it is usually offered without much qualification or reservation yet is quite difficult to prove and verges on tautology. One can, of course, define as 'natural selection' any change in relative frequency of some genetic variant. But that is then just a description, not a scientific statement--even though it seems by far to be the normal practice, especially among those not formally trained or knowledgeable in evolutionary theory (such as many if not most human geneticists).
We have described two means of differential proliferation of genetic variants, organismal and functional selection, which are completely consistent with evolutionary history as the basis of the origin of biological traits, but are different from classical Darwinian natural selection. In organismal selection, organisms explore and choose 'niches' as they are called, or ways to live. Functional selection simply refers to failed development or function if some contributing molecule just doesn't work in a satisfactory way. In organismal selection, organisms are proactive rather than passive, and there is another way this can happen as well.
Organisms, even plants, explore their environment and where possible go where they can do well. They choose or 'select' their environment. This can have a genetic basis and serve as a source of evolution of complex traits that are not just the product of competitive natural selection. But organisms can also alter their environment to make it, in a sense, the way they'd like it to be. This is known as nice construction. The term was first used, to our knowledge, by Olding-Smee, Layland, and Feldman in the 1990s; if there was a former coining of the term, we are not aware of it. You can see more at the Wikipedia entry by the same name, which gives examples.
|Beavers constructing their niche in Tierra del Fuego. Wikimedia.|
The idea is that individuals in a species modify their environment, and that in turn makes the environment suitable for the species. Earthworms modify the soil which is then good for earthworms (Darwin, who wrote an interesting book on earthworms, knew about this!). Earthworms have genes 'for', that is genomes whose effects function well in, the particular environment. This alteration of the environment is not the same as an 'autonomous' environment screening competing organisms. In that sense, the evolution of niche constructors and their niches is not the same as passive natural selection.
|Harlaxton Manor, England. Wikimedia|
Niche constructors extroadinaires: you and me!
Of course we humans are the pinnacle of niche construction today--though bees, ants, and even earthworms and perhaps even such species as corals and bacterial biofilm makers do this very well at their own scale and pace. That makes one wonder what ulterior motive lurks in the minds of those who are obsessed with finding genetic reasons for every little facet of our normal behavior, including sociocultural traits.
That point aside, not all niche construction is 'intentional' the way beavers intentionally build their dams or we build manor homes. But to the apparent great extent by which evolution proceeds very slowly in assembling complex traits, including behaviors, it is not clear how much good old-fashioned natural selection is responsible or required for the ability to modify the environment. Likewise, organismal selection may be an important part of the gradual accretion of such powers, with those who bore appropriate genotypes finding the modified environment and modifying it further. A tiny beginning could make it such that most of the evolution is by non-'Darwinian' means.
The usual argument is that there is a back-and-forth feedback between natural selection and niche construction. But whether this is a chicken-and-egg debate about which came first, and how and when and to what extent natural selection was important, niche construction is clearly an example of evolution by means beyond the usual view. Again, as with our other examples, niche construction doesn't 'overthrow' Darwinian processes, but it does show that the classical view needs to be nuanced. And, again, nothing mystical or even mysterious or strange is involved!