Saturday, 3 April 2010

Peer Review

In the preceding post (below) I mentioned what I think is a key failing of evolutionary scenarios, such as that of the eye by Nilsson & Pelger - they completely ignore what we now know of the genetic and molecular mechanisms that are essential for forming biological tissues. And along with this they ignore the fact that the evolution of substantially new biological structures, such as eyes and feathers, would require new genes to arise.

And my point here is this: this knowledge has been well known for at least a generation; yet, not only did N&P (and authors of comparable scenarios for other organs) feel free to ignore this, but presumably the reviewers of their paper were happy to overlook this oversight too. And, we should note, it wasn’t published in some minor or obscure journal, but in the prestigious Proceedings of the Royal Society of London.

Before I comment further on peer review, let me also mention another serious flaw in the authors’ rationale. Their aim was not only to show what they considered to be a plausible scenario for the evolution of an eye, but also to estimate how long it would take - to show that there was plenty of geological time for it to happen. But their method was seriously flawed: their calculations used an equation (in Falconer’s Introduction to Quantitative Genetics) formulated to estimate the time to effect change through domestic breeding.

First of all, this reinforces the point I made previously - that their model for the evolution of an eye is based on selection from an already existing gene pool - completely ignoring the fact that a new organ such as an eye will require very many new genes (which are prohibitively improbable to arise - a central theme of my book).

Second, their model assumes that only those organisms having a variation that confers at least a 1% improvement in vision will contribute to the next generation. This is the sort of thing a breeder can put into practice, but totally unrealistic to think that natural selection (which of course is what the evolution of the eye would have had to rely on) will operate this way - most of the mature individuals (even those with reduced visual acuity) in a population will have some offspring.

So these criticisms completely undermine their claim that their calculations are a ‘pessimistic’ estimate of the time for an eye to evolve. Quite the opposite!

This also gives some insight into peer review: Presumably the reviewers were so happy with the overall message of the paper that either (a) they didn’t examine it too closely, and/or (b) they were aware of its serious shortcomings but chose not to stand in the way of a paper which said what they want to hear. At very least It shows that ‘peer review’ is not the independent objective assessment it’s claimed to be.

And its not just the reviewers who are at fault. This paper is referred to widely to support the notion that eyes could have evolved readily. Have none of these bothered to take a careful look at what N&P actually proposed?

Eye Evolution

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.