Two neuroscientists say that a now-extinct race of humans had big eyes, child-like faces, and an average intelligence of around 150, making them geniuses among Homo sapiens. The history of evolutionary studies has been dogged by the intuitively attractive, almost irresistible idea that the whole great process leads to greater complexity, to animals that are more advanced than their predecessors. The pre-Darwin theories of evolution were built around this idea; in fact, Darwin’s (and Wallace’s) great and radical contribution was to throw out the notion of “progress” and replace it with selection from among a set of random variations. But...