In this year of all things Darwinian I’m surprised how often I hear it said that it was Darwin who thought up the concept of evolution.
He did not.
The idea of evolution – of organisms changing their characteristics over time – had been around for quite a while before Darwin’s day. The problem was that no one had managed to figure out correctly why or how it occurred until Darwin came along. The brainwave of Darwin (and Alfred Russel Wallace and perhaps a few other, totally forgotten, individuals) was in coming up with the process by which evolution worked – a process described by Darwin as natural selection.
Here’s a little ‘prehistory’ of the theory of evolution.
In the 1790s Erasmus Darwin (Charles’ grandfather, and an eminent thinker in his own right) wrote Zoönomia, in which he suggested that all warm-blooded creatures arose from one “living filament” and had “the power of acquiring new parts” in response to external stimuli in the environment, with these improvements being inherited by successive generations.
In the first decade of the 1800s Jean Baptiste Lamarck drew upon the knowledge of the age and proposed what was up until then the most complete evolutionary theory to be put forward. He postulated that evolution was powered by two dynamics: a natural tendency for the complexification of life forms and a tendency of those life forms to adapt themselves to their specific surroundings or environments. It is the second of these postulations for which Lamarck is most famous. He considered it likely that evolution may occur due to the fact that the features that an organism acquired during its lifetime were passed on to its descendants (This is in line with the ideas that were held by others at the time).
Thus, to use a human example, if a child had parents who were athletes then the child would inherit the strong muscles that the parents had developed as a result of their sporting activities. Equally, if a child had parents who were couch potatoes the child would inherit the excessive fleshiness and the atrophied legs of the parents. This is commonly known as the theory of evolution by acquired characteristics. Here’s a caricature or cartoon of Lamarck that I’ve created using a contemporary portrait of the man and a wood engraving of a giraffe by Thomas Bewick (from around the same time). The concept behind the caricature is a tribute to the iconic caricature of Charles Darwin as an ape that you can see in my previous post.
The choice of a giraffe in my image is a reference to the common use of this animal as an example of the theory of evolution by acquired characteristics in action. According to the theory the giraffe’s neck was so remarkably long due to the fact that competition between different animals for food encouraged giraffes to stretch upward in order to eat leaves that were beyond the reach of other creatures, causing their necks to strengthen and lengthen – and that this lengthened neck was passed on to their descendants.
What’s the difference between this theory and the theory of evolution by natural selection? According to the theory of evolution by acquired characteristics the new, evolved features that are possessed by the offspring of a creature are features that were deliberately cultivated by the parent (such as a giraffe stretching its neck). With natural selection however, the features are simply random variations. (Darwin, who coined the phrase ‘natural selection’, was actually slightly unhappy with the term, as he felt that people may think that it implied deliberate, conscious selection rather than the purely automatic process that he intended.)
According to natural selection, when a creature has offspring, those offspring all vary very slightly in quite random ways (such as by being slightly different colours, different sizes and so on). Some of these offspring, purely by chance, will be better suited for survival in their particular environment (By being a different colour, for instance, they may blend in with their surroundings better, and thus be less likely to be seen by a predator). These offspring will thus be more likely to survive and have their own offspring – which will on average have inherited the same fortunate variation that improved the survival chances of the parent. Thus the trait will be passed on from generation to generation.
Let’s look at an example of the process in action (taken from my forthcoming book on the nature of ‘things’). Imagine an animal that lives in a very cool, though not freezing cold, sub-Arctic climate. Say a type of fox. The climate’s pretty nippy, but the fox has fur, so it survives quite comfortably. Gradually, over a very long period of time (quite a few fox generations) the climate changes as the earth moves into one of its periodic ice ages. The fox’s world gets noticeably colder and harsher. As the climate gradually cools, successive generations of fox are seen to sport longer and thicker fur that helps to keep them warm. The foxes’ coats get longer almost in step with the cooling climate. This looks very much as though the fox has decided to grow more fur to suit the new conditions. But it isn’t so. Here’s what really happens. Whenever a fox has a litter of cubs each cub will inevitably be physically slightly different from the others. Some will be larger, some smaller, some stronger, some weaker, some darker, some lighter, some more furry, some less furry, and so on. Imagine that a pair of foxes has a litter of three cubs: one that’s more furry than its parents, one with the same amount of fur as its parents, and one with less fur than its parents. On average, that’s exactly the fur-distribution that you’d get in a typical litter of three. These three cubs are born into a world that’s slightly colder than the one that their parents were born into. The cub that has less fur than its parents finds the conditions too harsh, and dies of hypothermia. The other two cubs survive. However the cub that has the same amount of fur as its parents finds the going tough in the cold, so it grows up to be a less than perfectly healthy specimen of foxdom. The third cub – the one with the most fur – survives quite well because it is adequately insulated from the cold. This cub grows and thrives. It mates with another fox that has thrived (which quite probably also had slightly more fur than its parents). The resulting cubs produced by this coupling will have similar traits to their parents – though as usual with minor variations, including a variation in the density of their fur. Imagine that this pair had a litter of three cubs, just as described for the parents above: one that’s more furry than its parents, one with the same amount of fur as its parents, and one with less fur than its parents. If these cubs were born into a world that was continuing to cool down the cub that would be most likely to survive would be the one with the thickest fur. This cub is slightly more furry than its parents, but is noticeably more furry than its grandparents. So it is that if the furriest offspring of each generation are the ones that survive the whole species becomes more furry in small steps. I must emphasize the fact that the survival of any individual fox is purely the luck of whether or not its characteristics mesh well with the prevailing conditions. I have just described the scenario in which the fox cub with the thickest fur survived as the climate cooled: however if exactly the same three cubs had been born at a time when the climate was warming up instead, the fox cub with the least fur would have been the most likely one to have survived (as its more thickly furred siblings would have found their own stifling coat a hindrance, just as you yourself find a thick coat a burden on a hot day).