The age of the Earth-9: Biologists join the geologists against the physicists

By Mano Singham

Fleeming Jenkin (a physicist, engineer, and collaborator of Kelvin) had, in a review of Origins, delivered a severe critique of Darwin's theory. He pointed out that not only was the time available insufficient for natural selection to work, but that the then-dominant theory of 'blending inheritance' (which said that children had a mixture of the qualities of their parents) worked against Darwin's theory, since even if one parent experienced an advantageous mutation, that person's child would only have half of it because the other parent would not have it, the grandchild one-fourth, and so on. The mutation would thus get diluted and disappear over time, and not grow and dominate the population, as natural selection argued.

Darwin had in fact already anticipated this difficulty and pre-emptively suggested that if the mutation occurred in several people and they mated with each other, then the dilution of the advantage would not occur and the population could grow. But he knew this was a weak argument. As a result, by 1880 Darwin was yielding somewhat on natural selection, saying that he had never argued that it was the only mechanism at work, which was true. He had always allowed for some Lamarckian influence though he was not fond of the idea. He now started giving greater room for Lamarckian mechanisms than he had done in the past.

But he was still hopeful that natural selection would eventually weather the storm caused by the short time scales, and that new understanding about the physics of the Earth and the rate of species change physics might vindicate his theory. Writing in his final published statement on the topic he said:

With respect to the lapse of time not having been sufficient since our planet was consolidated for the assumed amount of organic change, and this object, as urged by [Lord Kelvin], is probably one of the gravest as yet advanced, I can only say, firstly that we do not know at what rate species change as measured in years, and secondly that many philosophers are not yet willing to admit that we know enough of the constitution of the universe and of the interior of our globe to speculate with safety on its past duration. (Burchfield, p. 79)

When Darwin died in 1882, he was widely mourned as a great scientist who had convinced the world that the theory of evolution is a fact from which there is no going back. But the vindication of his theory of natural selection had to wait another thirty years.

In the previous post, I said that by the end of the 19th century, geologists had started balking at the ever-reducing ages of the Earth coming out of physicists calculations, most of the latter based on thermal cooling models developed by Kelvin and going back to Buffon. They felt that 100 million years was as far as they were willing to go. Some physicists were also starting to question Kelvin's models and the values of the thermodynamic parameters on which his calculations depended.

Biologists were also getting tired of being pushed around by the physicists. Perhaps emboldened by the resistance from geologists and some physicists, they too started arguing that the evidence from paleonotology for an old Earth was too strong to be dismissed, and that the cause of any discrepancy with the results from physics lay with physics and not with biology.

The professor of zoology at Oxford Edward Poulton (1856-1963), in a talk to the British Association in 1896, picked up on some recent critiques of Kelvin's work by other physicists that had pointed out that if one changed Kelvin's assumptions of the thermal properties of the Earth by relatively small amounts, the age of the Earth could be made to increase by a factor of over fifty. Poulton then made the case as to why the case for an older Earth based on biological and paleontological evidence should not be dismissed. He pointed out that:

[E]volution results first in the divergence of general characteristics and then of specific characteristics, that natural selection requires much longer to alter simple organisms than more complex ones, and that the origin of no phylum can be found anywhere in the stratified record – he proceeded to argue that the degree of specialization found in the lower fossils can only be accounted for by a very long period of evolution prior to the beginning of geological record. (Burchfield, p. 139)

He concluded that the physicists must be wrong about their young Earth.

This was the state of affairs near the dawn of the twentieth century. It was an impasse, with geology and physics at loggerheads, and the theory of evolution by natural selection hanging in the balance, whose fate would be decided by which side would emerge the ultimate winner.

(Main sources for this series of posts are The Chronologers' Quest: The Search for the Age of the Earth (2006) by Patrick Wyse Jackson and Lord Kelvin and the age of the Earth by Joe D. Burchfield (1975).)

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

This series is archived here.