A good example of where belief in evolution is maintained because people aren’t prepared to look at the detail is in the supposed evolution of new organs such as the eye.
The eye is the classic example of a highly specialised organ, considered by many pre-Darwinian scientists such as John Ray as incontrovertible evidence of design in biology. Even Darwin recognised that the eye was a challenge to his theory, but in the Origin speculated how it might have arisen progressively from a simple light-sensitive tissue through a series of variations.
In the 1990s a couple of Swedish scientists, Dan-E Nilsson and Susanne Pelger (Proceedings of the Royal Society of London Series B - Biological Sciences, 256:53-9), expanded on this sort of scenario, illustrated as follows:
Starting from a patch of light-sensitive cells (which is a huge presumption in itself, though I can’t expand on that here) it is envisaged that an eye evolves by a flat patch of cells becoming a depression, which gradually deepens into a small pit (a to c), the neck of which then narrows (d). Each of these stages, taking place over several generations, is driven by the advantage of increased optical acuity (better resolution). When this stage has been reached, further improvement can be achieved only by addition of a lens (e), and the authors boldly assert that ‘Even the weakest lens is better than no lens at all, so we can be confident that selection for increased resolution will favour such a development all the way from no lens at all to a lens powerful enough to focus a sharp image on the retina.’
The totally unjustified assumption in this scenario is that if a variation will offer some advantage, then we can be sure that it will arise. No thought whatsoever is given to the crucial question of how those variations will arise. I think this blind spot (!) has arisen for two reasons.
First, before we knew about genetic and molecular mechanisms, it was thought that biological tissues were innately plastic in the sense that variations would arise spontaneously, and favourable ones could then be passed on. However, we now know that the formation of morphological structures – whether it be an eye, feather or leaf – is not by some sort of vague plasticity, but through the closely orchestrated action of many genes. So new structures need new genes. But in the above scenario, all that we have learned in the last 50 years about the biochemistry of tissues and the molecular mechanisms involved in forming tissues is totally ignored.
The second reason arises from the fact that much variation is possible through the mixing of genes that are already available. For example, it’s been known since well before Darwin that domestic varieties of crops and animals can be developed by breeding selectively from those individuals which have the desired variations (which have arisen naturally). But it was also well-known that there are limits to the amount of change that can be achieved this way. Which is why, although artificial selection could validly help to illustrate natural selection, Darwin’s contemporaries also knew that domestic breeding could not support changes such as the evolution of new organs. We now know why: new organs need new genes and molecular mechanisms to construct them - which are not available in the genomes of the original parents.
This oversight is illustrated by the fact that the above-mentioned authors’ calculation of the rate of eye evolution is based on selection from an existing pool of genes. Whereas there can be no doubt at all that the evolution of an eye would require very many new genes – for several proteins used exclusively in the eye, and for the molecular mechanisms that construct the eye in the course of embryological development. So their comment about a lens arising simply because it would be advantageous to do so is just ignorant wishful thinking - scarcely science at all.
There are so many speculative scenarios for the evolution of new structures - whether they be for eye, wing, feather, limb or whatever - but they are no better than those available in the 19th century - because they are based on the assumption that biological tissues are plastic, and completely ignore the genetic and molecular implications. If proponents of evolution want their scenarios to be taken seriously then they really do need to take on board the genetic and molecular detail.