We all have in mind that evolution from one species to the next has occurred thanks to a succession of small changes, creating, at the end of the day, big changes. One selected change represents a possible adaptation to the environment. But was each innovation optimal in terms of efficiency? The human machine, from a biological as well as a psychological point of view, can appear improbably complex, reaching perhaps perfection, which would tend to make us think that a good intentioned God has had his word to say in all this.
However, looking at things in a more pessimistic way, we only consider the omnipresent occurrence of physical or mental disease, or the effects of ageing, all these “defects” which seem inherent to human nature, and we can’t help wondering why they survived to natural selection. There are theories explaining these “defects” in terms of adaptations, but they are only partly satisfying and surely don’t explain everything. So are Humans, and the other species who have won at the natural selection game, at the top of perfection? Are we the uncontested winners of a great contest?
On these questions, two major specialists of evolution have differing opinions. One one side of the ring: UK ethologist and evolution theorist Richard Dawkins, famous author of “The selfish gene” in 1976. For him, the only engine of evolution is adaptation of species to their environment. As soon as one individual or group of individual is better adapted than others, his genes will be passed down in priority to the next generations. This vision supposes a permanent fight between gene lines, those who carry the most useful adaptations winning a little more replication than others. The different species and the different individuals in one environment would therefore be constantly competing for long term survival of their genes. After a gigantic numbers of generations, it would be reasonable to imagine that those that are still there are safe in most new competitions, and are therefore close to perfection, at least in stable environmental conditions.
Opposite him on our ring: American paleontologist Steven Jay Gould, professor of geology and history of sciences at Harvard, deceased in 2002. This other evolution theorist has had the opportunity to notice that the basic body plan of species living today has not changed for a long time, even though there was enough time for it to evolve into a potentially better adapted version. Does that mean that the existing body plans are at the top of perfection in terms of adaptation to their environment? That seems a little surprising… Thinking about it, eyes behind my back or a couple of extra arms could have come in handy (well, for as much as sexual selection would allow this kind of thing, but that’s another issue)… Has competition stopped somewhere in the way, only ever looking at small details after that?
That’s not all: It would seem that all the body plans existing today have appeared on earth at more or less the same period, during the Cambrian explosion. Since then, no major innovation in the basic organization of these beings has occurred. On the other hand, the number of differing body plans of individuals has diminished since the Cambrian era (even if the number of different species, being identical in terms of body plan, has itself increased). Why has the Cambrian era given birth to so many novelties in terms of body plans? Why many of these plans have today disappeared? Why did the only novelties occurring after the Cambrian era only concern adaptive traits (like human intelligence), but not new ways of building and organizing bodies? Even passing from the aquatic environment to terrestrial environment has not generated huge changes in species. The basic plan has remained the same (snails, worms,…), but with adjustments to terrestrial environment.
What is important to remember is that natural selection can only act on already existing organisms, and in a very slow and laborious way, and that it is always at risk, at any time, of being extinct due to various more or less natural causes. That’s what makes Gould think that if everything had to start again since the origins of life, the result today would possibly be very different than it is.
We must get used to the idea, the species existing on earth today are not necessarily the best possible adaptations. Chance has had its word to say, and we were maybe not all meant to be precisely this way.
However, we can imagine that, all environmental constraints being equal, certain things would anyway have remained identical. There are not that many different ways of moving, of stocking energy. Let’s not therefore fall into adaptationnism, which consists in considering every trait observed in a species or even in an individual as an adaptation.
Let’s consider the eye. It has obviously been selected for and optimized because it gives the great advantage of seeing what’s around. But how about other traits, like for instance the color of blood? It’s only red thanks to the presence of hemoglobin to carry oxygen to our cells. The same reasoning could be made, according to S. J. Gould, concerning the number of fingers of our hands. Fossils have been found with various numbers of fingers at the end of each member, going up to eight. So why five fingers would they be more adaptive than six or eight? It’s probably simply a matter of chance if the mother species, the one having more luck than others in the natural selection and extinctions game, happened to have five fingers.
So Dawkins seems to think that if we are here today it’s a victory over chance, and that we have been selected by the Evolution human resources department thanks to our biological CVs. Gould, on the other hand thinks that that It’s in great part thanks to chance if I am here sitting at my desk, with all my attributes, and that I was only helped by the fact that my ancestors were there before me and have avoided plan shots of restructuring… OK so it's not as glorious but isn't it slightly more pleasing to think this way?