Serendipity Design overkill

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THE GENERAL view of evolution is that it results in a creature that is perfectly suited to its task, with every single trait contributing to its ability to thrive, survive and multiply. For example, rattlesnakes are so well adapted as predators that they can attack even when they are dead.

A pair of doctors in Arizona, Frank LoVecchio and Jeffrey Suchard, had read stories in local newspapers describing how rattlesnakes, after being shot or bludgeoned to death, had inflicted serious injuries. They decided to investigate the matter further, and followed up every case they could find during the course of a year.

The doctors discovered that 15 per cent of rattlesnake bites occurred after death. In one case, a person picked up a decapitated head, holding it at the back of the neck, so that the fangs pointed away, but the dead head twisted around and injected venom, causing the man eventually to lose a finger. In an even more extreme case of rattlesnake resurrection, a headless snake leapt to attack a person, its bloody neck hitting the target. If the head had still been in place, the fangs would have bitten, and the attack would have been successful.

All of this demonstrates the extent to which evolution has hard-wired the snake's attack mechanism, thereby circumventing the snake's brain and quickening the attack. The infra-red and touch sensors remain active for a short period after brain death, and continue to initiate well-aimed assaults.

The rattlesnake appears to demonstrate the efficiency of evolution. It seems to have developed a series of attributes which are all vital to its survival. Everything is exploited and there seems to be no room for redundancy. However, according to a recent article in New Scientist magazine, there is some evidence to suggest that snakes, and some other creatures, are over-designed. Xavier Bonnet, a French zoologist who was studying tiger snakes in western Australia, chanced upon a curious injury suffered by many of the snakes. The seagulls of the region had the habit of pecking out the eyes of tiger snakes, and consequently 10 per cent of them were blinded.

Bonnet studied these blinded snakes, and discovered that they were able to find mates and hunt just as well as sighted ones. They grew to the same length and weight as sighted snakes. This was important evidence in favour of a theory put forward by Carl Gans, a biologist at the University of Texas. Gans has been arguing that animals, having evolved a trait during one phase of their history, often retain that trait, even if it is no longer of any use millions of years later. In the case of the tiger snake, vision must have been useful in the past, but other senses have since taken over and yet the eyes have remained in place, even though they are of no benefit to the snake's survival.