Monday, July 21, 2014

On the mythology of natural selection: Part V. Niche construction

The usual Darwinian presentation of adaptive life assigns essentially all of it to natural selection, in which, going back essentially unaltered to Darwin, constraints of the environment (including overpopulation relative to resources, and competition for those resources, and predators, and competition for mates and territory) screen contending alternatives and allow some to reproduce more and others less.  We model this traditionally in terms of relative success within a local population with its local ecological circumstance, rather than in absolute terms.  And while competition is among organisms, the usual theory is that it really is all about genes and their  proliferative success.

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.

Niche construction
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!


Anonymous said...

Thank you for this piece. It preempts my comment and questions.
Do not organisms “compete” (adapt) against the total ever-changing environment whether niche or otherwise, not just other organisms? Is it not the environment (physical and social, harsh or lenient) that drives selection or more accurately, doesn’t materially interfere with the success of an organism bearing certain old or newly acquired traits by accidents of DNA replication, translation etc. and epigenetic control?

On to my fantasy about niche creation:
Has Religion and all its’ accoutrements created a world-wide niche environment in which adaption (God resides in the human brain) has occurred and is occurring still? Success in this niche is awarded to believers. It seems they do better. Besides a belief system that helps take the angst out of the unknown, pain, suffering and death adds to success by encouraging humans to proceed with hope despite the uncertainties of life. The placebo effect is very powerful “trait” in human psychology.
Religiosity is so widespread one can wonder whether it survives as a successful trait. Is there any evidence for such a notion?
Similarly other “psychological traits” putatively have been given survival benefits, such as greed and co-operation.
Lastly, is Sweden a niche environment that favors social and co-operative behaviors?
Some of these musings would be more likely if “free will” as some neuroscientists have speculated, were an illusion. Much behavior however is unconsciously initiated.

Ken Weiss said...

Alfred Wallace's idea of evolution was about groups competing against environmental constraints (we discuss that tomorrow, I think, in the context of 'group selection'. A regular Darwinian form of selection would say that we individually compete for resources and what counts is how we do that compared to our peers from the same species. In other words competition is for resources, not just (say) fighting with each other (that can be a form of sexual selection, also discussed tomorrow).

I can't comment on religion per se, but culture certainly is part of our human way of life. If it helps us gang together and gang up on other groups of humans, it could be seen as group selection. A number of authors have tried to fit religion into a Darwinian framework (e.g., The God Gene, Darwin's Cathedral, others).

Anonymous said...

How did fish become amphibians then terrestrial? Are my notions of evolution off the wall? I have no formal training in evolution to order my notions.
I presume Aquatic life diversified by random accidents of gene expression. Many forms evolved successfully and are still successful today through the Holocene (some in niches?).
A number of (co-related?) accidents of gene expression (altered gene products) produced organisms (walking fish etc.?) that the now harsh (ground and air, not water and dissolved oxygen) environment did not materially impede reproductive success. This led to diversity on land.
Diversity (random tinkering with DNA expression) gradually evolves forms that are “immune” to physical environmental impediments to reproductive success, even when there are few (no) other organisms that one had to compete with. Who did the first amphibians compete with?
I have difficulty ridding my brain of the notion that evolution is ultimately a contest between diversity and environment. Am I “Wallacean”?

Ken Weiss said...

Response on fish/amphibian comment.
Thanks for your comment and questions. I am by no means an expert on the emergence of terrestrial vertebrates, and can only give you a generic answer.

First, these things usually happen very slowly indeed (too slowly to notice if you were there at the time--and 'the time' may means millions of years), and usually locally not worldwide at the same time.

The general idea, and it's consistent with our post series, genetic variation arises by mutational change in DNA that is random -- that is, doesn't occur because of any particular function or need. It may affect the structure of proteins or RNA, or of their usage (expression), or it may have some other sort of function.

Some ways or other, the changes enabled the organisms to gradually move into life without being submerged all the time. Breathing, locomotion, and who knows what other functions (I certainly don't!) gradually, probably not very synchronously on the day-to-day time scale, accumulated.

The organisms with these variants, which would be 'advantageous' relative to the new environment rose in frequency.

You say in rather non-technical terms roughly what happened, but again very, very slowly compared to just listing off the changes as we tend to do.

This process involved and was enabled by genetic change. It could have been classically Darwinian by involving competition for limited resources, say, at a lake or ocean shore or something. Or some 'fish' could have gradually (countless generations) acquired the ability (say) to make some grooves in the sand that would have some water in them but let them move onto land and be 'semi-wet'. Or those who could absorb oxygen through their skins managed to jump to or move around on land for a bit. Or they may have been (for a very long time) in an area where there were limited food resources and being able to scrounge from the shore's edge did give an advantage.

Any of the set of ways of differential proliferation of genetic variation that we discuss in this series may have been involved. And it's not likely we know enough to parse them. But, again, a text on amphibian evolution is likely to be far more specific about time and place than I can -- though it may or may not attempt to go beyond the standard natural selection account.

I don't think you are bing particularly Wallacean. It's just that he tended to stress the competition of groups vis-a-vis their environment compared to Darwin's stress on inter-individual competition.

Go on line and find "Wallace's Ternate paper", and you'll be able to see his elegant (and short) statement of his view--the paper that stunned Darwin and led to the 1858 presentation of their ideas.

Longterm evolution as far as we know is about changing genetic variation in time and space. If there are other unknown factors, well, they'll just have to be added to our theory if/when we discover them. Our series was intended to show that reliance on raw competition for limited resources, which motivated both Darwin and Wallace, is not the only thing that happens. One reason for writing our posts is the stress that so many writers, popular and even scientific, place on the standard Darwinian part--and apply it to human affairs in ways we think careless and unjustified.