Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane Read Free Book Online

conclusion. Play back the film of life, says Conway Morris, and life will flow down the same channels time and time again. It will do so because there are only so many possible engineering solutions to the same problems, and natural selection means that life will always tend to find the same solutions, whatever they may be. All of this boils down to a tension between contingency and convergence. To what extent is evolution ruled by the chance of contingency, versus the necessity of convergence? For Gould all is contingent; for Conway Morris, the question is, would an intelligent biped still have four fingers and a thumb?
    Conway Morris’s point about convergent evolution is important in terms of the evolution of intelligence here or anywhere else in the universe. It would be disappointing to discover that no form of higher intelligence had ever managed to evolve elsewhere in the universe. Why? Because very different organisms should converge on intelligence as a good solution to a common problem. Intelligence is a valuable evolutionary commodity, opening new niches for those clever enough to occupy them. We should not think only of ourselves in this sense: some degree of intelligence, and in my view conscious self-awareness, is widespread among animals, from dolphins to bears to gorillas. Humanity evolved quickly to fill the ‘highest’ niche, and a number of contingent factors no doubt facilitated this rise; but who is to say that, given a vacated niche and a few tens of millions of years, the kind of foraging bears that break into cars and dustbins could not evolve to fill it? Or why not the majestic and intelligent giant squid? Perhaps it was little more than chance and contingency that led to the rise of
Homo sapiens
, rather than any of the other extinct lines of
Homo
, but the power of convergence always favours the niche. While we are the proud possessors of uniquely well-developed minds, there is nothing particularly improbable about the evolution of intelligence itself. Higher intelligence could evolve here again, and by the same token anywhere else in the universe. Life will keep converging on the best solutions.
    The power of convergence is illustrated by the evolution of ‘good tricks’ like flight and sight. Life has converged on the same solutions repeatedly. While repeated evolution does not imply inevitability, it does change our perception of probability. Despite the obviously difficult engineering challenges involved, flight evolved independently no less than four times, in the insects, the pterosaurs (such as pterodactyls), the birds, and the bats. In each case, regardless of their different ancestries, flying creatures developed rather similar-looking wings, which act as aerofoils—and we too have paralleled this design feature in aeroplanes. Similarly, eyes have evolved independently as many as forty times, each time following a limited set of design specifications: the familiar ‘camera eye’ of mammals and (independently) the squid; and the compound eyes of insects and extinct groups such as trilobites. Again, we too have invented cameras that work along similar principles. Dolphins and bats developed sonar navigation systems independently, and we invented our own sonar system before we knew that dolphins and bats took soundings in this way. All these systems are exquisitely complex and beautifully adapted to needs, but the fact that each has evolved independently on several occasions implies that the odds against their evolution were not so very great.
    If so, then convergence outweighs contingency, or necessity overcomes chance. As Richard Dawkins concluded, in
The Ancestors Tale
: ‘I am tempted by Conway Morris’s belief that we should stop thinking of convergent evolution as a colourful rarity to be remarked and marvelled at when we find it. Perhaps we should come to see it as the norm, exceptions to which are occasions for surprise.’ So if the film of life is played back over and over