Darwin’s treatise on evolution wasn’t the first and wasn’t the only attempt to explain the diversity of life.
“The only novelty in my work is the attempt to explain how species become modified,” Darwin later wrote. He did not mean to belittle his achievement. The how, backed up by an abundance of evidence, was crucial: nature throws up endless biological variations, and they either flourish or fade away in the face of disease, hunger, predation and other factors. Darwin’s term for it was “natural selection”; Wallace called it the “struggle for existence.” But we often act today as if Darwin invented the idea of evolution itself, including the theory that human beings developed from an ape ancestor. And Wallace we forget altogether.
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[O]n November 22, 1859, Darwin published his great work On the Origin of Species by Means of Natural Selection, and the unthinkable—that man was descended from beasts—became more than thinkable. Darwin didn’t just supply the how of evolution; his painstaking work on barnacles and other species made the idea plausible.
It’s important to understand that last bit, and it applies in all of science. Saying, “I can explain that” isn’t sufficient. You need to amass scientific evidence in support of your claim — data that supports you and eliminates other explanations, along with predictions that would falsify your theory if they fail to come true.
And Darwin was always better at amassing evidence like that than Wallace. Wallace just didn’t have the patience or the punishing work ethic Darwin did.
Plus when Darwin published, he was in England but Wallace was in Africa at the time. Darwin did credit Wallace in Origin of Species, however.
Also, Darwin never claimed his work to be completely original. Other works speculating on possibly evolution (and not just scientists either, there were popular books out there for the masses). As well, Darwin’s own grandfather Erasmus Darwin paved the way for Lamarck’s theories. Which, while wrong, were still important for Charles’s work.
I thought Wallace was in South East Asia.
The thing with Darwin’s theory is that few people believed it (and to be fair, they had little reasons to). But while they refused evolution by natural selection, they found his arguments convincing enough to believe that evolution happened.