A Far More Satisfactory Theory

The legendary American folk singer Pete Seeger sounds like a thoroughly good chap: not only did he actively participate in the American civil rights movement of the 1960s, and inspire an excellent album by Bruce Springsteen, but, according to a recent story in the Guardian newspaper, nowadays he'll spend hours in [the Beacon Sloop] club, mischievously giving out bumper stickers reading "Gravity - it's just a theory" and encouraging people to send them to anyone in Kansas, heartland of the anti-Darwinism, creationist movement.

Nice one, Pete.

Seeger isn't the first to compare gravity and evolution. Darwin himself made a similar comparison in the oft-quoted and wonderful (albeit grammatically incorrect) final sentence of On the Origin of Species:

There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Darwin's point is that people have no difficulty accepting that the motion of the Earth is determined by set physical laws, so why not the formation of species as well? It's an excellent point. It would be interesting to know where evolution-deniers draw the line. (Actually, spare me the emails, no it wouldn't.)

In a land rich in scientific heroes, Darwin and Newton are Britain's (and, perhaps, the world's) two greatest. It is entirely appropriate, therefore, that these two great men are buried within nodding distance of each other in Westminster Abbey, the final resting place of many of Britain's national heroes.

The real beauty of Newton's Law of Universal Gravitation is its simplicity: the gravitational force between two masses is proportional to the product of the masses and inversely proportional to the square of the distance between them. How simple is that? And yet, from so simple a beginning, we can predict the motions of the tides and planets, and send people to the moon.

The effects of gravity are all around us. They are part of our everyday world. We constantly observe and are constrained by them, while hardly giving them a second's thought. But we can measure them if we care to. I'll never forget the thrill of calculating the acceleration due to gravity in my bedroom as a boy, armed only with a length of cotton, a ruler, a wristwatch, a pocket calculator, and a squash ball for a weight. My result (9.91ms^-2) was within 1% of the official figure. Universal Newtonian gravitation, it seemed, also held true in my bedroom.

True, a precocious young man named Albert Einstein did eventually iron out a few Newtonian anomalies by coming up with a slightly more accurate explanation of gravitation (begging Newton's posthumous forgiveness as he did so), but classical Newtonian gravitation is still good enough for people living in the real world, rather than imagining themselves riding on beams of light.

As with gravity, the effects of Darwinian evolution are all around us. We see them in the pigeons in our streets, the spiders in our bathtubs, and the opposable thumbs on our hands. Yet most of us hardly give them a second's thought. And, as with gravity, precocious young whippersnappers have amended and improved Darwin's original theory, but its original essence is still very recognisable in the latest thinking.

But here the comparison begins to break down. Where Darwinian evolution differs from Newtonian (and, indeed, Einsteinian) gravitation, for the time-being at least, is that we do not yet have an observable mechanism for gravity. What actually makes gravity work? Yes, physicists can hypothesise about gravitons and gravitational waves as much as they like, but they have not yet been able to detect either of them in the laboratory (and I will surely never be able to detect them in my bedroom).

Darwinian evolution, on the other hand, certainly does have observable mechanisms driving it: variations amongst the individuals of a species, heredity and—Darwin's big idea—Natural Selection (capital 'N', capital 'S'). We can see all of these mechanisms at work on a daily basis, if we take the trouble to look. We can see them in our streets and gardens, on our bird feeders, and in the cobwebs on our bedroom ceilings. Everywhere we care look, Nature is still red in tooth an claw.

Darwinian evolution does not rely on mysterious, unobservable particles or waves; its mechanisms are in action all around us in our everyday world. Which is why, although Newtonian gravitation has a certain attraction, it seems to me, Darwinian evolution is, in this way at least, a far more satisfactory theory.

This article was written in 2007.

The existence of the Higgs Boson was effectively confirmed on 4th July, 2012.