Before the “Origin,” similarities and differences between species were mere curiosities; questions as to why a certain plant is succulent like a cactus or deciduous like a maple could be answered only, “Because.” Biology itself was nothing more than a vast exercise in catalog and description. After the “Origin,” all organisms became connected, part of the same, profoundly ancient, family tree. Similarities and differences became comprehensible and explicable. In short, Darwin gave us a framework for asking questions about the natural world, and about ourselves.
He was not right about everything. How could he have been? Famously, he didn’t know how genetics works; as for DNA — well, the structure of the molecule wasn’t discovered until 1953. So today’s view of evolution is much more nuanced than his. We have incorporated genetics, and expanded and refined our understanding of natural selection, and of the other forces in evolution.
But what is astonishing is how much Darwin did know, and how far he saw.