The Science of Sin takes on a lot of religious baggage, for all that Jack Lewis, its author, says that he’s an atheist. To some extent that’s inevitable given his background, and his choice to shape the book around the concept of the Seven Deadly Sins, looking for neurological and evolutionary explanations for the origins of each — both their pitfalls and their utility.

The problem is that it inevitably becomes very moralising. He does try to point out when certain neurological things might not be someone’s choice, but he seems to have more sympathy for paedophiles than for fat people, and is very certain that being fat is almost totally a choice people make (when in fact there are many contributing causes, including sheer poverty, where good food choices are not always available), and a moral one that impacts badly on society and on everyone around them. Fatness is also unequivocally bad for you, in Lewis’ view, where the real picture is more mixed (fat people, for instance, have lower 30-day mortality from bacterial pneumonia and have better survival rates and reduced immune depletion when living with HIV) and thinness is no guarantor of health of any kind.

(Important note: this is not something I’m interested in debating in the comments on this blog. I’ve studied some of the science of nutrition in relation to immunity as part of my MSc, but you’re best off heading to the literature with an open mind and a careful eye for bias — your own and that of the papers you find.)

In almost every chapter, he finds a way to reference narcissism, blame fat people, suggest fat people are narcissistic, and so on. And again, he treats these as moral issues, failures that people should rectify.

In some cases, he isn’t wrong, but he’s replacing religious moralising about it with a kind of secular moralising about it that sits badly with any effort to be objective. Combine that with his reliance on scans like fMRI to tell us about what’s going on in someone’s brain, and a lot of his conclusions are questionable: you can get apparently significant results from the brain of a dead salmon, with fMRI, an issue that he very briefly references before waving it away and saying that fMRI is the tool we have, so he’s going to use it.

For me, there was a kind of entertainment value in watching him build up his argument, but I was aware of the one-sided nature of his search for appropriate sources, and not appreciative of his moralising.