We are surrounded by a limitlessly complex world. Plants, although simple and green on the surface, contain intricate machineries that allow it to wield its photosynthetic powers. Humans, too, have developed extremely complicated functions over a tortuous and long path known as evolution.
Evolution is commonly thought to be moving in a certain direction: from simple to complex. For example, we know that creatures like the spider are much more complex than its bacterial ancestors from billions of years ago. However, some scientists have argued that this directional aspect of the theory of evolution does not explain how natural complexities came about and have proposed an alternative explanation.
Dan McShea and Wim Hordijik, the lead researchers of a study published in Evolutionary Biology, proposed that evolution progressed the other way — from complex to simple. They argued that functions like our visual or nervous system could not have possibly developed incrementally over time. They referred to these functions as “irreducibly complex,” suggesting that an organisms would never have had an eye or a brain that was half functional. An idea that could reconcile the existence of “irreducibly complex” structures and natural selection has been included in their study.
Through extensive computational works, McShea and Hordijk have proposed the idea of complexity by subtraction, an idea that originally, body structures may have started out more complex and were selected to become simpler over time.
McShea and Hordijk used computer simulations to study the likelihood of their theory. The two scientists also looked at a biological example: the skull. There is an acknowledged trend towards fewer components as the skull developed from fish to amphibians to reptiles to mammals. This reduction in skull bones occurs as bones are lost or fused together, and demonstrates an overall reduction in the complexity of the skull.
Right now, complexity by subtraction is just being proposed as an alternative theory to how some structures in living organisms could develop. “There’s enough here to be intrigued by this mechanism (and yes, I am intrigued!), but not enough to judge its importance, at this point,” McShea wrote in an email to The News-Letter.
He also addressed some arguments that his research may contradict the Darwinian theory of evolution that has been accepted for so long.
“Interestingly, there is some lively web chatter at the moment coming from creationists and intelligent-design folks who believe that our argument undermines Darwinism. It looks like they’ve latched onto the idea that we’re offering a non-standard view of how complex structure arises. (We are, but it’s perfectly consistent with Darwinism, and indeed invokes natural selection to explain the subtraction.) Anyway, just for clarity, let me say that our story for how complexity originates is non-Darwinian. It’s based on the principle that any parts in an system will tend spontaneously to become more different from each other, simply by the accumulation of accidents. That is truly non-Darwinian, although not anti-Darwinian. It doesn’t contradict natural selection. It just doesn’t need it. The second part of our story is very Darwinian. Once you have a complex system, with many different part types, natural selection starts removing the unnecessary ones and sculpting the remaining ones to function more efficiently.”
McShea also plans to study the idea further and see if he can find more evidence of the occurrence of complexity by subtraction in nature. “As for future research, what I’ll be doing is looking for possible cases of complexity by subtraction that might be worth looking into more deeply. The vertebrate skull that we looked at in this paper was one of those opportunistic cases that on close examination actually supported the complexity by subtraction idea. I’ll be looking for others.”