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Extinction of the Dinosaurs left Living Space for Mammals

Extinction of the Dinosaurs Left a Large New Niche for Mammals

Howard Falcon-Lang, reporting for the BBC, tells us in an article entitled “Space is the Final Frontier for Evolution” that research by a Canadian student of Indian extraction, Sarda Sahney, and colleagues at the University of Bristol suggests that Charles Darwin may have been wrong when he argued that competition was the major driving force of evolution. It has led to a flurry of creationist and right wing websites gloating that the theory of evolution has finally had its coup de grace.

The central idea of Darwin was his explanation of why evolution occurred, evolution as a fact having been realized already by many intellectuals at the time. What was missing was an explanation of why it happened, and that is what Darwin gave. Darwin came from a wealthy family living in the countryside, so he was aware of how farmers selected the best stock to breed from. It gave him the idea of “natural selection”—that overpopulation led to competition for valuable resources among individuals of a species, as well as between species, so that the organisms that were best able to obtain the resources needed for life survived, and those unable to get sufficient resources died early, and did not survive overall. Ability to get the resources needed, Darwin called “fitness”. Only the fittest survived in the long run and so the idea was called at a later date “survival of the fittest”.

The environment that the organism lived in effected the selection by culling animals unable to get the resources they needed. Darwin was impressed by Malthus’s ideas on the growth of population. Populations would grow exponentially until they saturated the resources available, then organisms previously able to graze abundant resources comfortably, found themselves struggling to get a share of the now scarce resources. The ones successful in getting sufficient to survive on until they found a mate and reproduced would have offspring to continue their line. Characteristics were inherited, Darwin wasn’t sure how, but Mendel founded the study of genetics and provided a mechanism. So the young of any species able to reproduce would carry the characteristics of their successful parents—the ability to obtain scarce resources in competition with others of their own kind and other species seeking the same resources. So, organisms battled for supremacy and only the fittest survived.

The Bristol study suggests the availability of “living space”, rather than competition, is the driving force for evolution. Studying fossils the scientists showed from evolutionary patterns over 400 million years of history, that biodiversity closely matched the availability of living space over time. Professor Michael Benton said they did not find that competition played any role in the pattern of evolution.

By living space, the scientists were actually referring to a suitable ecological niche to live in. The ecological niche concept of biologists is that environments have within them ecological niches that a species can occupy. A niche means that particular resources are available to an organism fitted to use them, and so any such organism can thrive free of competition from any other species that is not fitted to occupy that particular niche. It includes such as the availability of food and a favorable 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, niches not available to other animals, triggering a new evolutionary burst. Similarly, the extinction of the dinosaurs left many niches empty, or left large volumes of living space open, free for the still surviving mammals to move into. It challenges the notion of “nature red in tooth and claw”, that intense competition for resources in overcrowded habitats is the major driving force of evolution. Professor Mike Benton, a co-author on the study, told BBC News:

Competition did not play a big role in the overall pattern of evolution. For example, even though mammals lived beside dinosaurs for 60 million years, they were not able to out compete the dominant reptiles. But when the dinosaurs went extinct, mammals quickly filled the empty niches they left and today mammals dominate the land

However, Professor Stephen Stearns, an evolutionary biologist at Yale University, US, told BBC News he found the patterns interesting, but the interpretation problematic:

To give one example, if the reptiles had not been competitively superior to the mammals during the Mesozoic, then why did the mammals only expand after the large reptiles went extinct at the end of the Mesozoic? And in general, what is the impetus to occupy new portions of ecological space if not to avoid competition with the species in the space already occupied? What is the impetus to occupy new portions of ecological space if not to avoid competition?

Stearns is showing that it was competition against the superior dinosaurs that kept the mammals in their minor position as little more than rats scurrying around the feet of dinosaurs for millions of years, the whole of the period the dinosaurs dominated the earth, because mammals arose at about the same time as the dinosaurs but were unable to find any niches to expand into. The dinosaurs had nearly them all. Once the dinosaurs died out, the competition was removed and the mammals could move into the “living space” dinosaurs had once occupied.

Darwin was aware of the importance of empty niches, because he had studied the Galapagos finches, which had themselves found a plethora of empty niches when they found their way to the islands, and began to diverge into different niches available. Why did they not all just move into the same niche? Plainly it was because competition in the favored niche was fierce once sufficient of the finches had bred. Thereafter, the birds could avoid such fierce competition by going for some other niche, and diversified.

Isolation of any segment of a species on to an island was recognized as a way in which evolution could speed up. The small number on the island were not likely to have a typical distribution of genes, and the conditions were not typical of those of the whole original population so the match between the characteristics of the sample and the resources available were not as well matched as they had been among the whole group. Quicker evolution is the outcome.

So, there seems on the face of it to be nothing really new in the Bristol paper except the viewpoint or emphasis. Eldredge and Gould’s hypothesis of punctuated equilibrium has suggested that evolution happens in spurts after long periods of stability, and the opening of “living space”, or the emptying of niches by large extinctions is one reason why spurts might happen, climatic and geological change might be other reasons for major change, and there could be many others down to new predators or new diseases affecting particular species that had been stable for long periods until this novel event happened.

So, it is hard to see anything in this new work that is revolutionary, and certainly nothing to stimulate creationist triumphalism. Indeed, the incomprehendable thing about the creationist fuss about Darwinism is that Darwin’s ideas could be utterly superceded by something new like this, but the mechanism that explains how evolution happens is not evolution. The theory can change, but the facts of evolution will simply remain to be explained. If it is to be Intelligent Design (ID), then the manifest facts of Unintelligent Design by an Omnipotent God (UDOG) have to be addressed by the creationists.


Written by mikemagee

25 August, 2010 at 10:18 pm

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