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Tim Lewens in Eurozine:

“What”, asked the distinguished evolutionist Michael Ghiselin in 1997, “does evolution teach us about human nature?” The answer he gave will surprise those who suppose that the evolutionary sciences describe the deepest and most ubiquitous aspects of our psychological makeup. Ghiselin informed his readers that evolution “teaches us that human nature is a superstition”. Why would anyone say such a thing? Doesn't talk about human nature amount to talk about the ways we are all the same? What could be objectionable about that? We can begin to understand the problems if we look back 180 years.

On 2 October 1836, HMS Beagle landed at Falmouth. She had finally returned to England, after a five-year circumnavigation of the globe. One of the Beagle's passengers was a 27-year-old Charles Darwin. After disembarking he first went to stay at his father's house in Shrewsbury, but by March of 1837 he had moved to London. It was here that Darwin began to speculate in a series of notebooks on a wide range of topics in natural history and beyond. He formulated his “transmutationist” view of how species had come into existence, he pointed to intense struggle as the primary agent of change in the natural world, and he reflected openly on the impact this image of life's history might have for human psychology, morality and aesthetic sensibilities. Many of these notebook jottings were transformed, in 1842, into a short “sketch” of Darwin's theory. By 1844 that short sketch had expanded into a 230-page statement of the evolutionary view. But it was not until 1859 – 15 years later – that the Origin of Species was published. What had Darwin been doing in the meantime?

The answer is that he spent the eight years between 1846 and 1854 working on a gigantic study of barnacles. This period – sometimes referred to as a “delay”, as though Darwin was ready to publish the Origin in the mid-1840s, but somehow lost his nerve – was a puzzle to historians for some time. But it now seems clear how Darwin used his barnacle work as a detailed empirical testing ground for many of his earlier theoretical speculations. One of the most important lessons Darwin took from his meticulous study of barnacle anatomy concerned the ubiquity of variation: “Not only does every external character vary greatly in most of the species”, he wrote, “but the internal parts very often vary to a surprising degree”. He went so far as to assert that it is “hopeless” to find any part or organ “absolutely invariable in form or structure”.

More here.