Pretty much everyone agrees that natural selection acting on random genetic mutations can explain some things. The really interesting question is, how much can it explain? Since Darwin’s mechanism seems intuitively plausible, we’re often tempted just to trust our intuitions rather than to look at the hard data. And yet the data increasingly show that, whatever its intuitive attractions, the powers of selection and mutation are surprisingly limited. In many cases, new biological functions require several mutations. And everyone agrees that natural selection doesn’t have foresight. But it’s widely assumed that if each of the individual mutations leading to new functions are themselves adaptive, then natural selection can traverse the pathway. Again, this makes intuitive sense. But what about the Read More ›