Let the blind see …
Breeding blind fish with blind fish restores sight
Posted on homepage: 11 January 2008 (GMT+10)
This is the pre-publication version which was subsequently revised to appear in Creation 30(4):54–55.
In a fascinating result, researchers have taken fish living in caves that have no capacity for vision, and by breeding them together with other strains of blind cave fish, have been able to observe at least partial restoration of sight in quite a few of the offspring of such crosses.1
Strangely, evolution-enthusiasts often get excited about blind fish, thinking it demonstrates evolution, when in fact the opposite is the case. Doubtless this find will, as has already happened, be reported in glowing evolutionary terms, so let’s look at it closely.
We’ve previously commented (see Blind fish, island immigrants and hairy babies, also this other article) on how blind cave fish in general are clearly the result of the loss of previously functioning eyes—a downhill change, or deterioration. Such processes of deterioration are not something that will add up over long time periods to give rise to new, complex functions and structures. Quite the opposite, in fact.
How do cave fish become sightless?
All fish living where there is light will sometimes have mutations (genetic copying mistakes) that will ‘mess up’ some aspect of the way eyes normally develop. Such fish will be at a disadvantage, so they will not usually survive to pass on their defective genes. Such defects will therefore be eliminated—an important function for natural selection in a fallen world; slowing down the rate at which living things degenerate.
But where some fish are cut off from the surface and find themselves in total darkness, the ones that are sighted now no longer have this enormous advantage over their blind cousins. And in addition, those with eyes now have the modest but real disadvantage of being prone to have eye injuries and/or infections as they bump into cave walls, for example.
So in short order, natural selection will now work the other way, to favour fish without eyes. This is almost certainly how we see populations of cave fish which are all totally blind, generation after generation, showing the ‘scar’ of where eyes used to be in their sighted forebears.
Robust research, riveting results
The researchers in this case were looking at four separate populations of the blind Mexican cave fish Astyanax mexicanus. Their (correct, in our view) reasoning was presumably that such a complex thing as the development of functioning eyes could be prevented by more than one type of genetic damage. So there was no reason to think that each of these blind populations had suffered the same kind of mutation.
So when they made various hybrids of these four populations, it was a satisfying vindication of that reasoning to note that some of the offspring had at least a semblance of vision. In fact, in some of these crosses, ‘nearly 40 percent … could see.’2
Because the same defect (eye loss) was caused by different genes being damaged in each of the populations, ‘when you cross them, the genetic deficiencies in one lineage are compensated for by strengths in the other, and vice-versa.’3
Head researcher, NYU Biology Professor Richard Borowsky, said, ‘Not only are the structures of the eye restored to the point where they regain function, but all the connections to the brain for proper processing of information not used for that enormous length of time are restored.’4
Of course, there is nothing in the experimental results indicating any ‘enormous length of time’. Borowsky is here just expressing the common belief in the timespans common to standard evolutionary reasoning. It would not take long at all, once a group of fish are cut off from the daylight by some geological circumstance, for an eye-losing mutation to be established by natural selection as described. If anything, the degree of restoration of even the brain connections suggests that there has not been enough time for significant mutational deterioration to occur in most or all of the genetic instructions needed for eyesight (remember that natural selection is not going to preserve any of the eye-constructing genes).
Note, too, that the information for creating eyes was not generated de novo in these sighted offspring by any evolutionary process but, as these researchers would agree, was there already, in the form of the genes inherited from their sighted ancestors.
So in addition to agreeing with the researchers about how the eyesight returned in the offspring, the take-home message of these results for creationists is that
- The results fit very comfortably in a framework of biblical creation history. This is not just because they highlight the devolutionary change involved in getting blind cave fish in the first place. It is also because the possibility of such a reconstruction would get progressively less likely, the more time that has elapsed since the fish were originally confined to their underworld existence.
- Talk of ‘evolution’ in relation to blind cave fish that descended from sighted ancestors is not appropriate if by that they mean the sort of change that can turn microbes into motor mechanics. Cave fish have arisen by processes that in fact demonstrate the opposite—deterioration of function, consistent with the ‘natural’ direction of genetic change in a fallen world.
- New York University, Progeny of blind fish can regain their sight, ScienceDaily Jan 8, 2008 http://www.sciencedaily.com/releases/2008/01/
080107120911.htm The work was formally published in an issue of Current Biology. Return to Text.
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