Natural Selection vs. Opportunity in Macroevolutionary Patterning of the Fossil Record

I'm going to talk about one or two peer reviewed papers, but in doing so, I'm going to have to say a few words ... and this will not be pretty ... about a certain science writer's report at the BBC.

In an article titled "Space is the final frontier for evolution, study claims" BBC "science writer" Howard Falcon-Lang uses the old, tired, and quite frankly, stupendously unethical tack of making a claim that Darwin has been overthrown by new research. If someone actually overthrows Darwin, then so be it. But this is not what has happened. Falcon-Lang, or perhaps his BBC handlers, have used the cheap trick to sell their wares, and this is not appreciated.

If Howard Falcon-Lang did not a) claim to be a science reporter and b) have a dumb-ass hyphenated name, I'd be nice in my critique of his recent writeup. But no. He left me no choice. I will have to take it apart red in tooth and claw.

Charles Darwin may have been wrong when he argued that competition was the major driving force of evolution.

OK, this is a little premature for me to say here, but as you read on you'll see that my assertion is justified: Mr. Falcon-Lang is not really in a position to make any kind of claim regarding the wrongness or rightness of a genius of the level of Dr. Darwin.

He imagined a world in which organisms battled for supremacy and only the fittest survived.

No. That is the world that so many hack science writers, creationists, and various Darwin detractors imagine. Darwin wrote endlessly about differential survival, differential reproduction, mate selection, and all the myriad forces that determine selection (and randomness). He did not imagine the thing Mr. Falcon-Lang imagines him to have imagined.

But new research identifies the availability of "living space", rather than competition, as being of key importance for evolution.

Never start a sentence, let alone a paragraph, with the word "but" especially when the rest of the essay is something one has essentially pulled out of one's "butt."

Now, a reality check: Living space, including nesting sites, feeding territories, reproductive or social territories, and just having space for a number of reasons has been on the books as a thing to compete over since ... well, since Darwin first talked about it. So has the actual focus of the paper in question: Niche space. Sub-habitats or resources that can be exploited by a particular type of organism. You know the drill: The woodpecker niche, the soil detritus niche, the niche of flight, etc. to which organisms are constantly shifting their adaptive positions. More of those equals more types of organisms, and since most species can not be of more than one 'type' (though some can, interestingly) that also means more species diversity.

Findings question the old adage of "nature red in tooth and claw".

I'm pretty sure this sentence/paragraph was supposed to be a heading but some dumb-ass editor screwed up. In any event, yes, there is an adage. We do not do science with adages. A science writer should know that. Adage indeed. There is also an old adage that one should never believe what is written by the press.

The rest of the essay is a description of the research, and is not terrible. Of course, Pagel and colleagues demonstrated that part of the key effect that is being observed here some years ago when they showed that species diversity correlates to the width of the continent better than to latitude in the New World, thus offering a better explanation for the pattern of species diversity than the "the equator has got lots of it" hypothesis. The rest of it: niche space, we also already had a good idea about, but this new study is more comprehensive and much larger scale.

Focusing on land animals - amphibians, reptiles, mammals and birds - the scientists showed that the amount of biodiversity closely matched the availability of "living space" through time.

Living space - more formally known as the "ecological niche concept" by biologists - refers to the particular requirements of an organism to thrive. It includes factors like the availability of food and a favourable habitat.

The new study proposes that really big evolutionary changes happen when animals move into empty areas of living space, not occupied by other animals.

For example, when birds evolved the ability to fly, that opened up a vast range of new possibilities not available to other animals. Suddenly the skies were quite literally the limit, triggering a new evolutionary burst.

This concept challenges the idea that intense competition for resources in overcrowded habitats is the major driving force of evolution.

OK, let's put aside the press report at this time. I'll just say this: It is quite possible that Mr. Falcon-Lang was the victim of some very bad messing around by an editor who is not a science writer. At the BBC. If so, I hope he lets us know that so we can all write letters of complaint to said editor.

Getting back to the point at hand, what the paper actually says is this, from the abstract:

Tetrapod biodiversity today is great; over the past 400 Myr since vertebrates moved onto land, global tetrapod diversity has risen exponentially, punctuated by losses during major extinctions. There are links between the total global diversity of tetrapods and the diversity of their ecological roles, yet no one fully understands the interplay of these two aspects of biodiversity and a numerical analysis of this relationship has not so far been undertaken. Here we show that the global taxonomic and ecological diversity of tetrapods are closely linked. Throughout geological time, patterns of global diversity of tetrapod families show 97 per cent correlation with ecological modes. Global taxonomic and ecological diversity of this group correlates closely with the dominant classes of tetrapods (amphibians in the Palaeozoic, reptiles in the Mesozoic, birds and mammals in the Cenozoic). These groups have driven ecological diversity by expansion and contraction of occupied ecospace, rather than by direct competition within existing ecospace and each group has used ecospace at a greater rate than their predecessors.

The idea of empty niches being filled by the available taxa is not new, nor is the idea that an evolutionary "event" .... like some non-flying taxon developing the power of flight .... results in species radiation. What is new in this paper is that a survey has been done using relatively good available data that demonstrates this concept.

There has not been an overthrow of Darwin, though I'm sure various creationists will now incorrectly and inappropriately use this press report to suggest that there has been. There has not been the introduction of a new idea regarding macroevolution, though the work here is important and interesting. As is often the case with evolutionary biology, the specific role of natural selection (and in this entire discussion, read "natural selection" when you see "competition") vs. opportunity (read "drift"), and different people with different views will differentially see the role of one or the other as more important as they look at the same data. The realty of the situation is probably simpler: Competitive advantages have a chance of winning out, in the same way that buying a lottery ticket with better odds makes you more likely to win. But you'll probably still lose. But to even buy the lottery ticket, there has to be one of those little gas stations on the corner that sells them.

Pagel, M., May, R., & Collie, A. (1991). Ecological Aspects of the Geographical Distribution and Diversity of Mammalian Species The American Naturalist, 137 (6) DOI: 10.1086/285194

Sahney, S., Benton, M., & Ferry, P. (2010). Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land Biology Letters, 6 (4), 544-547 DOI: 10.1098/rsbl.2009.1024