A billion and a half years ago, life on earth was staggeringly dull. The ocean, once a steaming primordial soup, had become a cold, thin, dreary broth of look-alike organisms. Eukaryotic cells with internal structures had appeared, but multicellular creatures were scarcely a blip in the census. Life lazed through those doldrums for a million millennia.

Then something happened: some unidentified combination of environmental circumstance and genetic novelty triggered crazy diversification in the variety and complexity of animal life over tens of millions of years, climaxing in the so-called Cambrian explosion. By 530 million years ago the seas held all the bizarre creatures fossilized in the Burgess Shale (and popularized two decades ago by Stephen Jay Gould in his book Wonderful Life). Many of those animals were evolutionary dead ends, but a few were the progenitors of every animal alive today.

When Charles Darwin published On the Origin of Species in 1859, he touched off a Cambrian explosion in evolutionary thought. Naturalists had theorized about evolution for centuries before him, but their ideas were generally unfruitful, untestable or wrong. Darwin’s breakthrough insight was not that a simple mechanism—natural selection—made evolution possible. Rather it was that in organisms whose environment changed nonrandomly and whose reproductive success in that environment depended on inherited traits, evolution became inevitable.

In the decades that followed, Darwin’s ideas connected up with the nascent field of genetics and then, at an ever quickening pace, with molecular biology, ecology and embryology. The explanatory power of his concepts proved irresistible. Today, 200 years after his birth and 150 years after Origin of Species, Darwin’s legacy is a larger, richer, more diverse set of theories than he could have imagined.

Consider the notion of selection itself. What Darwin called natural selection was the competition for ecological resources often abbreviated as “survival of the fittest.” As H. Allen Orr describes, natural selection demonstrably drives much of evolution and speciation. Yet modern biologists have also elaborated greatly on Darwin’s ideas about sexual selection, in which members of a species compete for opportunities to breed. Kin selection and other forms of group selection are active areas of study, too, with theorists debating roles for selection at the level of single genes, individual organisms, whole species—or all of the above.

Meanwhile the sources of heritable variation go far beyond point mutations in genes, as David M. Kingsley explains. Such changes might facilitate the rapid evolution of complex traits.

Just as most of the weird Cambrian monsters eventually went extinct, many current hypotheses in evolution will also wither over time. Those that survive, however, will be inestimably powerful for explaining the natural world. We humans can also continue to use those ideas to make technologies more adaptable and robust. Why shouldn’t we learn from billions of years of nature’s experiments?

Note: This article was originally printed with the title, "Dynamic Darwinism".