Read an extended version of this article, and many more evolution myths, in our online special
It鈥檚 a theme endlessly repeated in wildlife documentaries. Again and again we are told how perfectly animals are adapted to their environment. It is, however, seldom true.
Take the red squirrel, which appeared to be perfectly adapted to its environment until the grey squirrel turned up in the UK and demonstrated that it is in fact rather better adapted to broadleaf forests.
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There are many reasons why evolution does not produce perfect 鈥渄esigns鈥�. Natural selection only requires something to work, not to work as well as it could. Botched jobs are common. The classic example is the panda鈥檚 鈥渢humb鈥�, a modified wrist bone that the animal uses like an opposable thumb to grasp bamboo. It鈥檚 far from the ideal tool for the job, but since the panda鈥檚 true thumb is fused into its paw, the panda had to settle for a clumsier alternative.
Evolution is far more likely to reshape existing structures than throw up novel ones. The lobed fins of early fish have turned into structures as diverse as wings, hoofs and hands. What this means is that we have five fingers because amphibians had five digits, not because five fingers is necessarily the optimal number for the human hand.
Many groups haven鈥檛 evolved features that would make them better adapted. Sharks lack the gas bladder that allows bony fish to precisely control their buoyancy, and instead have to rely on swimming, buoyant fatty livers and, occasionally, gulping air. Mammals鈥� two-way lungs are far less efficient than those of birds, in which the air flows in one direction.
Continual mutation also means that potentially useful features can get lost. Many primates cannot make vitamin C, an ability that wasn鈥檛 missed in animals that get lots of vitamin C in their diet. However, such losses can be limiting if the environment changes, as one primate discovered on long sea voyages.
Evolution鈥檚 lack of foresight also leads to inherently flawed designs. The vertebrate eye, with its blind spot where the wiring goes through the retina, is one example. Once natural selection fixes upon a bad 鈥� but workable 鈥� design, a species鈥� descendants are usually stuck with it.
Environments also change. In the arms race between predator and prey, parasite and host, species have to keep evolving just to maintain their current level of fitness, let alone get even fitter. As the Red Queen says in Through the Looking Glass: 鈥淚t takes all the running you can do, to keep in the same place.鈥�
Humans aren鈥檛 running fast enough. Evolving and adapting is a numbers game: the larger a population and the more generations there are, the more mutations will appear and the more chances there will be for natural selection to favour the beneficial and eliminate the harmful. Around 10 billion new viral particles can be produced every day in the body of a person infected with HIV; the total human population on Earth was no more than a few million until fairly recently. A bacterium can produce 100,000 generations in a decade, but there have probably been fewer than 25,000 generations since the human lineage split from that of chimpanzees. So it鈥檚 hardly surprising that in less than a human lifespan, we鈥檝e seen the evolution of new viruses, such as HIV.
Our evolution has accelerated in the last 10,000 years, but we are changing our environment ever faster, leading to problems ranging from obesity and allergies to addictions and short-sightedness. Viruses and bacteria might approach perfection: we humans are at best a very rough first draft.
Read an extended version of this article, and many more evolution myths, in our online special
