In 1996, palaeontologist Mike Benton published a fascinating analysis of tetrapod evolutionary data and concluded: "Competitive replacement has probably played a minor role in the history of tetrapods. In an assessment of the origins of 840 families of amphibians, reptiles, birds, and mammals, fewer than 26%, and probably fewer than 13%, were identified as candidate competitive replacements (CCR's)." The alternative mechanism proposed was adaptation into new habitats. This finding was presented in the paper as bringing a different emphasis to our understanding of speciation than was brought by Darwin:
"A classic view in evolution has been that many successful radiations of plant and animal groups in the Past have been mediated by competitive interactions. Newly successful groups are said to have outcompeted and displaced the previously established organisms, and hence to have demonstrated some progressive or advantageous feature. [. . .] The pattern of radiation of tetrapods, and indeed of many other groups, suggests that it is unlikely that competitive replacement was paramount."
The pattern of evolution of the vertebrates, showing the relative importance of the major groups through time. (Source and further details here)
Moving the clock forward to the present, with the benefit of a more comprehensive database, Benton has repeated the study. The authors say: "This is the first numerical study investigating the link between tetrapod taxonomic and ecological diversity on a global scale." The findings vindicate the 1996 study and the primary driver of diversification is said to be expansion into new ecospace. Competitive pressures are considered to be of limited importance because evidence for direct competition was not been forthcoming in the study. The emphasis was all on expansion:
"The data show multiple lines of evidence for the role of expansion as the main driver of tetrapod diversification: (i) tetrapods have only explored a third of habitable modes of life; (ii) tetrapods have occupied an exponentially increasing number of modes; (iii) ecological diversification has been driven at an increasing rate by the different tetrapod classes; (iv) successively dominant tetrapod classes have increased the maximum rate of mode utilization; and (v) Tetrapoda exhibit ecological incumbency, observed by a limit at which mode utilization decreased, except at times of mass extinction."
This interpretation of the data has been widely reported because it presents a significantly different picture than is found in the textbooks. BBC News carried the tagline: "Charles Darwin may have been wrong when he argued that competition was the major driving force of evolution." The report continued:
"He imagined a world in which organisms battled for supremacy and only the fittest survived. But new research identifies the availability of "living space", rather than competition, as being of key importance for evolution. Findings question the old adage of "nature red in tooth and claw". [. . .] This concept challenges the idea that intense competition for resources in overcrowded habitats is the major driving force of evolution. Professor Mike Benton, a co-author on the study, explained that "competition did not play a big role in the overall pattern of evolution"."
In her blog, Sarda Sahney, the PhD student who conducted the study with colleagues, identified the writer of the BBC report as Howard Falcon-Lang (the significance of this is the subject of comment below). She provides a summary of the take-home message of this research:
"[T]he rich biodiversity we see on Earth today has grown out of expansion, not competition. Darwin cited competition among animals, coined 'survival of the fittest', as a driver of evolution in his book, On the Origin of Species; since then competition has been considered key to having grown Earth's biodiversity. But while competition has been observed on a small scale, (eg. between species), there is little evidence of competition guiding large-scale shifts in biodiversity, such as the dominance of mammals and birds over reptiles and amphibians in today's world. Our new research supports the idea that animals diversified by expanding into empty ecological roles rather than by direct competition with each other."
Consequently, the implication of all this is that we need to do some hard thinking about Darwin's primary mechanism of evolutionary transformation: the natural selection of hereditable variations. The evidence from the fossil record does not support this account of origins. Instead, vertebrate radiations are expansive radiations into ecospace. Die-hard Neodarwinians should sit up and take note of this! However, the reactions of some are to protest about misreading the significance of the research reported. A member of NCSE staff, Steven Newton, wrote a strongly worded piece with the title: Darwin Was Not Wrong--New Study Being Distorted. His first target is the BBC report:
"Science fares poorly in the media. [. . .] When scientific topics are reported, they are consistently misunderstood and spiced-up with such sensationalism that the original significance is contorted beyond all recognition. Such misreporting has happened again--this time involving Charles Darwin and evolution.
A recent paper in the journal Biology Letters, "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land," by Sarda Sahney, Michael Benton, and Paul Ferry, has caused quite a stir. The normally-staid BBC wrote of this paper, "Charles Darwin may have been wrong when he argued that competition was the major driving force of evolution.""
The significance of Howard Falcon-Lang being the writer of the BBC report can now be clarified. Falcon-Lang is a professional scientist who has widely published in peer-reviewed literature. He writes as a scientist, not as a journalist picking up a story second-hand. He knows that the public needs to read both accurate and interesting science. Did he misunderstand the paper? According to Newton: "A press release for the paper noted that when examining large-scale changes in biodiversity, the data suggest: 'Animals diversified by expanding into empty ecological roles rather than by direct competition with each other'. This paper does not argue that Darwin's conception of small-scale competition within species is incorrect. It does not argue that new species arising out of accumulating changes is a flawed concept. It does not argue Darwin was wrong." Newton is the one misreading the paper, which sets out to identify factors relevant to biodiversification (the origin of species). It claims that competition between species, whether small-scale or large-scale, is not relevant to understanding the phenomenon. Darwin was not wrong to say that "small-scale competition within species" is a real occurrence - but he was wrong to think this phenomenon helps explain the origin of species!
In a previous blog, it was noted that sometimes it is OK to say Darwin was wrong. No one minds when it is said that Darwin was wrong about the origin of the domestic chicken. But there is tremendous resistance to any questioning of his more serious errors. This new work documents one of these. No one disputes that Darwin correctly documented competition between breeding communities and between different species. However, what is the evidence that this is relevant to the origin of species? This new research presents solid data showing that other factors govern vertebrate radiations on land. The ideas have been around at least since 1996, and it is now high time for Darwinists to cool their rhetoric and take these scientific findings on board.
Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land
Sarda Sahney, Michael J. Benton and Paul A. Ferry
Biology Letters, 2010, 23(4) 544-547 | doi: 10.1098/rsbl.2009.1024
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.
Benton, M. J. Testing the roles of competition and expansion in tetrapod evolution. Proceedings of the Royal Society B, 1996, 263, 641-646 | doi:10.1098/rspb.1996.0096
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