For a long period, some scientists have been sceptical of the process of natural selection, saying that certain biological structures are far too complex to be a result of it. Examples of such complex structures include the eye and the brain. Evolutionary theorists’ explanations have always been that they emerged from simple structures to more complex ones over a long time.
However, a new study published in Evolutionary Biology offers another point of view. The researchers explain that instead of evolving from simple structures into complex ones, many could have evolved from a far more complex one that gradually became simpler. The authors of the study, Dan McShea and Wim Hordijk, call this phenomenon ‘complexity by subtraction’. They write, ‘Standard thinking says that the evolution of complex functionality proceeds by the addition of new parts, and that this build-up of complexity is driven by selection, by the functional advantages of complex design. The standard thinking could be right, even in general. But alternatives have not been much discussed or investigated, and the possibility remains open that other routes may not only exist but may be the norm.’
The researchers used computer models and trends in skull evolution to back up their hypothesis. In the computer model, complex structures are represented by an array of white and black cells. Here, the cells can change colour according to a set of rules. A programme that mimics biological processes like reproduction, mutation and inheritance was also used along with it. When the cells were given tasks, the better they got at the given jobs, the chances of those cells getting passed on to the next generation became more probable. A few generations later, the pattern of the cells had evolved into simpler ones. Also, these later cells were more efficient at performing tasks.
They also cited previous studies on vertebrate skulls. According to them, fossil fishes’ skulls consisted of a number of bones, which became simpler over the course of evolution. As fish evolved into amphibians to reptiles, and finally to mammals, skull bones underwent dramatic changes. In some instances, the bones became fewer. In others, they got lost or fused.