Charles Darwin, born 200 years ago on Thursday, upended our conception of humanity's place in Nature but also unleashed a pernicious justification of social and racial inequality.
At its most extreme, what came to be known as "social Darwinism" was invoked to defend the practice of eugenics: enhancing the "quality" of the human race by weeding out -- through sterilisation, even extermination -- persons deemed feeble of mind, body or both.
Darwin, a Christian, a Victorian liberal and opponent of slavery, rejected these ideas as not only scientifically unsound but also morally repugnant.
But that did not stop them from spreading and persisting in one form or another up to the present day.
Adding insult to injury, the person who first sketched a theory of eugenics, Francis Galton, was a second cousin of Darwin.
Unaware of the influence of genes, Galton and most of his scientific contemporaries were convinced that traits acquired over a lifetime could be passed on to one's offspring.
He also assumed that some races were innately superior, giving comfort to racist theories that placed white Europeans at the pinnacle of evolution.
His claims were supported in the late 19th century by the pseudo-science of anthropometrics, which equated facial structure and skull capacity with intelligence.
Italian criminologist Cesare Lombroso went so far as to conclude that some individuals were born criminals -- "uomo delinquente," he dubbed them -- who could be unmasked through their physiognomy.
The use of slang, and ape-like features such as a narrow skull and an unusually mobile big toe, were brandished as proof that these irredeemable specimens were in fact a human sub-species.
"They speak like savages because they are true savages in the midst of our brilliant European civilisation," Lombroso wrote.
But it was British sociologist Herbert Spencer who coined the concept of social Darwinism, arguing that the same forces of natural selection guiding evolution applied -- and should apply -- to human society too.
Spencer summed up his philosophy with a phrase, later used by Darwin himself, that was to become a watchword for libertarians and laissez-faire economists for decades to come: "survival of the fittest."
When champions of the free-market system "justify the economic status quo as a struggle for life, they are reducing Darwin to a slogan," said Guillaume Lecointre, a professor at France's National Museum of Natural History.
At the end of the 19th century, a number of thinkers turned to Darwin and his insights about the natural world to justify different social and economic hierarchies, he said.
It was not hard to do. "In nature, one can find anything: the mirror image of democracy, a dictatorship, or a libertarian world," Lecointre said.
A poor understanding of genetic inheritance bolstered by dodgy intelligence tests, for example, were used to support a 1924 law in the United States severely restricting immigration from eastern and southern Europe, as well as non-European countries.
The historical abuse of Darwin's ideas has helped provoke a hostile reaction even to legitimate science that hits on a raw nerve.
When American biologist Edward O. Wilson in the mid-1970s created the discipline of sociobiology, whose central tenet is that human behaviour is largely determined by our genetic endowment, he was engulfed in controversy.
"Genes hold culture on a leash," he famously said.
More recently, the "nature before nurture" flame has been taken up by evolutionary psychologists, whose argue that even the most intimate choices we make in love and friendship are shaped by genetic imperatives.