Charles Darwin's theory of evolution by natural selection, and his related theory of sexual selection, completely changed the way biologists approach the study of life. What's more, the implications of his theories (including the notion that all living species, including humans, are descended from a common ancestor) revolutionized our views of who we are and where we come from. Yet there was a great deal that Darwin did not know, and it took more than a century before evolution was united with genetics, leading to the modern science of evolution. For example:
1. The biggest gap in Darwin’s knowledge was the nature of heredity. This was solved by Gregor Mendel's studies on pea plants; but remained largely unknown until the early 1900s, long after Darwin's death.
2. Darwin assumed that evolution is always slow; but we now know that evolution takes place very quickly, and we see exactly how evolution happens through carefully controlled studies in the field and in the laboratory.
3. Darwin's theory went a long way toward explaining how changes accumulate within a species; but he had remarkably little to say about when such changes result in the evolution of a distinct new species. We are now able to understand what a species is and how reproductive barriers allow changes that accumulate within isolated populations to develop into new species.
4. Darwin assumed that all evolution is gradual; but we can now trace major episodes in the history of life in which there was a relatively sudden increase in species (such as the Cambrian explosion) or a relatively sudden decrease in species (mass extinctions).
5. Darwin pioneered the idea that life's history resembles branches on a tree of life; but new evidence from fossils, comparative anatomy, and DNA show many branches Darwin did not know about and a degree of tangled cross-connection he would not have suspected. The iconic view of human evolution as a linear progression from hunched ape to upright man (popularized during Darwin's lifetime by Thomas Henry Huxley), has been replaced by a more complex, interconnected network of many humanlike species, with ours as the only survivors.
6. Darwin made the case that evolution is inevitable; but is it predictable? Evidence now reveals how often-unrelated life evolves somewhat predictably to converge on similar solutions, and life diverges when faced with extreme conditions many scientists had assumed too inhospitable for life at all.
7. Topics that puzzled Darwin were the peculiar and often-counterintuitive body designs, the coevolution of animals with flowering plants, and the paradox of ant societies with sterile workers.
There were many things that Darwin didn't know, and some things that he got wrong. But perhaps the most important thing that Darwin did not know is how fully his theories would become the basis for all of modern biology and offer new ways to view the world and our place in it. We now have evidence for evolution that was completely unavailable to Darwin, for example:
The few fossils known in Darwin’s lifetime had only begun to hint at the history of life.
Understanding how land masses have moved makes it possible to understand evolution.
Examples from many species provide some of the strongest evidence for a history of descent with modification rather than the special creation of YEC.
Natural Selection in Real Time
Wild species have been documented in the act of experiencing evolution by natural selection.
Universal Genetic Code
Darwin suggested that all of life might have evolved from a common ancestor, but we now know that every known type of life uses the same DNA code inherited from a single ancestor.
Such advances have made Darwin's views look even more prescient and essentially correct now than could have been realized in his time. The science of evolution is not just a historical science, allowing us to reconstruct the past and present. Evolution is also an ongoing process, a way to understand how all species will continue to change. In other words, evolution gives us a way to make predictions about the future—including our own future.