Friday, November 2, 2007

Expanding the Wheel?: Lotka's Max Power Principle and Human Ecology

A lot of blogs are about the most current and hottest new research published in a given field. For the blog to be interesting they have to get to it before most other people, often posting on papers that aren't yet released to the public. Or that's one approach anyway.

Going to another extreme, this is about a paper published in 1922 in PNAS by the influential physicist Alfred Lotka. The paper is titled "Contribution to the energetics of evolution." It's been cited thousands of times (unfortunately none of the citation indexes I have access to go back far enough to see how many) but I wonder what proportion of the people citing it have read it. A pdf of the paper is posted under week 12 (see sidebar to right). Yes it would have fit last week's theme better, but work with me here... It may alter the way you think about the world or you may just find it an interesting bit of science history - to read such an important paper that was published 85 years ago, count 'em, that's a lotta years.

The paper argues that a physical property underlies evolution by natural selection - the maximum power principle. A fairly concise view of the principle is given by the following quote:
"In every instance considered, natural selection will so operate as to increase the total mass of the organic system, to increase the rate of circulation of matter through the system, and to increase the total energy flux through the system, so long as there is presented an unutilized residue of matter and available energy.
This may be expressed by saying that natural selection tends to make the energy flux through the system a maximum…”

The point usually emphasized in the literature is this maximizing of flux through the system.

At the end of the paper, Lotka briefly ponders the relevance of his principle for an understanding of human evolution:
"We have thus derived, upon a deductive basis, at least a preliminary answer to a question proposed by the writer in a previous publication. It was there pointed out that the influence of man, as the most successful species in the competitive struggle, seems to have been to accelerate the circulation of matter through the life cycle, both by ‘enlarging the wheel,’ and by causing it to ‘spin faster.’ The question was raised whether, in this, man has been unconsciously fulfilling a law of nature, according to which some physical quantity in the system tends toward a maximum. This is now made to appear probable; and it is found that the physical quantity in question is of the dimensions of power, or energy per unit time…”

Lotka's views were echoed by a lot of later researchers who attempted to take a more thermodynamic view of human evolution - like Leslie White, Richard Adams, and Joseph Tainter. And were also applied to general biological phenomenal such as the evolution of body size (see Brown, Marquet, and Taper, The American Naturalist, 1993).

Its a classic and thought-provoking paper that should be read by everyone.


1 comment:

Beck said...

Am looking into relating Lotka to Liebig's Law of Minimum and Linares' Garden Plot Hunting.Will get back here later. If you have any insights please let me know. Thanks.

Locations of visitors to this page