Even though Wallace believed in spiritualism, could he be considered in any way a creationist or an early intelligent designer?
Again that becomes a matter of definition. He was an absolute hardcore natural selectionist. In fact, as he writes in his autobiography, in many ways he was more Darwinian than Darwin in this regard. The big thing that he did drop the ball on, and he first announced this about ten years after the publication of the Origin, was that he decided that natural selection could not account for the evolution of humans. It deeply disturbed Darwin to lose his co-discoverer on this critical point on the theory of evolution. He wrote Wallace, “I hope you have not murdered too completely your own and my child.” In this regard you could legitimately call Wallace a creationist. He was a non-materialist in terms of one aspect of the evolutionary process.
How did Darwin and Wallace differ on their understanding of the evolution of humans?
Wallace deemed there to be some kind of divine intervention. He was not a theist in the sense of believing in God or even a polytheist. His vision of the divine was of this nebulous, multifarious spirit world. Wallace believed that humans are endowed with spirit and that is what lingers on and you can communicate with post-mortem.
And Darwin was basically by the book: natural selection has created humans. For him, mankind evolved in the same way as mice and fruitflies did. He had no need of divine intervention in the evolution of humans.
Did Wallace’s work advance the idea of speciation more than Darwin’s?
Yes, I think so. You can’t really discuss the mechanism of speciation whereby one species splits into two until you have a very concrete notion of what species are. So you need a good definition. Darwin’s definition of species is essentially that there are extreme varieties. Think of varieties of a rose, you can have a pink rose and a yellow rose and if you keep going along that line of variability eventually you’ll have a different species. And I should add that it was sort of rhetorically necessary for Darwin to do that given his argument, because people were comfortable with the notion of two different varieties of rose from their Victorian gardens. So all he’s saying is, look, there’s nothing mysterious about this; there are slightly more different varieties and we call them species, which is true, but you need something more illuminating, you need some notion of where that cutoff occurs. We now recognize typically that it’s where the members of one population cease to be capable of interbreeding with members of the other population.
When does this definition of species originate?
There’s a big literature on this, but the most exquisite statement of this fact is made by Wallace in his butterfly paper from 1864-65, where he writes that species are these groups of individuals capable of interbreeding with others within the group but not with individuals from outside the group—they’re reproductively isolated from each other. Very few people know that Wallace came up with this definition of species. This idea—it’s called the biological species concept—is certainly one of the most important ideas in evolutionary biology in that speciation is really the engine of biodiversity. You’ve really got to come to terms with speciation if you want to understand the generation of biological diversity.
What was Wallace’s reaction to his secondary role in relation to Darwin?