This interesting history of the 'first Darwinian left' fills a gap in the literature and is a challenge to the attempted 'sociobiologization' of the left by Peter Singer in his book on Darwinism and the left. The author rightly points out the problems with Singer's false jeremaid about leftist views on evolution. Unfortunately the left has always been confused about Darwin's theory (they aren't the only ones!) and the result has been a consistent confusion on the subject. The author here is careful to assert his allegiance to the Neo-Darwinian synthesis, and the selectionist theory, which isn't surprising, and the text takes its place in the standard critique of evolutionary psychology typical in Gould, Rose, and Lewontin. The problem is that this approach doesn't wash, and yields the debate to the ideologists. Attempts to set the record straight, as here, never succeed, because they bite on the hook of Darwin's theory, whose selectionist holy writ _is_ the source of the ideology the left should have exposed from the start. In fact, Marx did expose it, but his views on the subject never really clarified themselves, and the Engels and Second Internationale mania for Darwin ended up dogma.
In any case, the book has a lot of interesting material on late nineteenth century thinking absorbing Darwinism. It wasn't all 'Social Darwinism', or at least that's the author's take. The point should be granted within limits, but the overall argument fails, I think, because the original Darwinism was flawed. Let it be noted as long as you think natural selection is a valid explanation you will never see the ideology in action in the theory. The left has always fumbled the ball here, and Marx is on record (with his brief interest in Tremaux's weird theory) as expressing his doubts about natural selection. Naturally that fact is shunted aside. So, Marx quietly had it right, at one point, and post-Hegelian that he was, he was the last with a sense of 'universal history' to alert him to the fallacy in Darwin's theory. But the Engels infatuation swept the field and we are left with a left that is a laughing stock, the defenders of last resort of an ideology, guard dogs that didn't bark.
Anyway, the author's swipe at Singer is well justified, and rubbing the left's nose in sociobiology as a gesture to destroy socialist thinking was a reprehensible deed. Bravo, for that.