What a Wonderful World by Marcus Chown Read Free Book Online Page A

accumulates different mutations, so the populations gradually diverge. Eventually, the two groups can no longer interbreed.
    There could be many reasons for this. It could be that a mixture of their genes simply does not lead to a working organism, in much the same way that putting a motorbike engine in a Rolls-Royce does not create a viable car. Or it could be that members of one group hang out on a particular type of fruit, waiting for a mate, whereas members of another group prefer another type of fruit entirely; though they could easily mate, they miss each other like ships in the night. In the case of insects, which have complex genitalia, two groups might no longer interbreed because one develops sex organs that, like a skeleton key and a Yale lock, physically do not fit each other.
    Whatever the reasons for groups of creatures diverging from each other, natural selection has populated the world with a myriad distinct species, each with as little ability to breed with each other as humans and oak trees.

The explanatory power of Darwin’s theory
    Darwin’s theory explains so many aspects of the world. For instance, it explains why life on Earth is so staggeringly diverse, boasting more than 5 million living species. It also explains why we share around 99 per cent of our DNA with chimpanzees – and even a third with mushrooms. This is exactly what would be expected if we evolved from a common ancestor. Since changes in genes accumulate over time, the DNA differences reflect the fact that the common ancestor of humans and chimpanzees lived relatively recently whereas the common ancestor of humans and mushrooms lived in the very remote past.
    Arguably, the most remarkable DNA sequence on Earth is GTG CCA GCA GCC GCG GTA ATT CCA GCT CCA ATA GCG TAT ATT AAA GTT GCT GCA GTT AAA AAG. 10 It is present in every single living organism – even in organisms not technically classed as alive such as giant mimiviruses. The reason the sequence is so widespread is that it existed in the common ancestor of all life. Carrying out a crucial process, it has remained unchanged for 3 billion years: the oldest fossil in your body.
    Darwin’s theory also explains why our antibiotics become less and less effective with time. Initially, they may kill the overwhelming majority of bacteria infecting a person. However, genetic variation within a population of bacteria ensures that some, inevitably, will survive to reproduce. Each successive generation will, therefore, contain a higher proportion of antibiotic-resistant bacteria, until eventually the antibiotic is next to useless. ‘Evolution is … an infinitely long and tedious biologic game, with only the winners staying at the table,’ says Lewis Thomas. 11
    Most of all, however, Darwin’s theory explains the illusion of design – why organisms are so perfectly suited to their environments. The reason a finch on an island in the Galápagos has a beak perfect for cracking open the nuts it lives on is because its ancestors prospered, leaving more offspring than did finches with less effective beaks. The shape of a beak turns out to be controlled by a single gene, slight variants of which express different proteins in the growing jaw of a finch embryo.
    The remarkable thing is that such an exquisite match between organism and environment is achieved without a designer. But, then, the natural process identified by Darwin is not random. ‘Mutation is random,’ says Richard Dawkins. ‘But natural selection is the very
opposite
of random.’ 12 It preferentially culls all the variants except those that confer on their host the ability to survive to reproduction. Incrementally, generation by generation, it accumulates advantageous changes, slowly but surely assembling machines far more exquisite and complex than any designed by humans. ‘The whole trend of life, the whole process of building up more and more diverse and complex structures, which we call evolution, is the very opposite of