The God Argument: The Case Against Religion and for Humanism. By A.C. Grayling. Bloomsbury; 269 pages; $26 and £16.99. Buy from Amazon.com, Amazon.co.uk

The Bonobo and the Atheist: In Search of Humanism Among the Primates. By Frans de Waal. Norton, 304 pages; $27.95 and £18.99. Buy from Amazon.com, Amazon.co.uk

ALONGSIDE angst vampires and “mummy porn”, godlessness has offered a reliable leg-up onto the bestseller list. These days, however, the market for antireligious tracts is sufficiently crowded that any new entrant needs a unique selling point. Two new books, from a philosopher and a primatologist, hope to inject something fresh into the argument.

“The God Argument”, by A.C. Grayling, a British philosopher, is concerned with tone. Other writers about religion, such as Christopher Hitchens or Sam Harris, pour out heated criticism. Mr Grayling promises to turn down the temperature. He claims (somewhat dubiously) to have written the first book “thoroughly and calmly to examine all the arguments offered in support of religious beliefs”, without the ill-temper that so often characterises many of these debates.

The first half of his book attacks both the human institution of religion and the intellectual idea of a God, or of supernatural beings in general. Mr Grayling is precise and incisive. He rattles through the standard arguments against the existence of God, and does a capable job of demolishing those put forward in the hope of proving a deity’s existence.

Yet his dispassionate approach has its drawbacks. Mr Grayling’s attack on religion is a competent piece of popular philosophy. But as a piece of proselytising, it is somewhat wide of the mark. Mr Grayling may be correct, for instance, that the “ontological argument” (which aims to prove the necessity of God’s existence through some creative arguments about the meaning of the word “greater”) is logically dubious. But few religious people base their beliefs on such rarefied reflection, a point that Mr Grayling himself concedes. The fact that his language is often austere and abstract, and peppered with the jargon of academic philosophy, merely compounds the problem.

The second half of the book, in which Mr Grayling sets out his take on the ethical system known as humanism, is more likely to win converts. Religious apologists frequently argue that morality would collapse in the absence of a God to enforce it. Mr Grayling has no time for such worries. He defines humanism as an approach to life that relies on two premises—that there are no supernatural beings and that ethics must therefore be drawn from human experience. He traces its history from early classical thinkers such as Democritus, Epicurus and Lucretius to its revival during the European Renaissance, and shows how its principles can be applied to thorny questions of love, death and how to live a good life. Mr Grayling is a talented apologist. His brand of humanism comes across as sensible, reasonable and characterised by a generosity of spirit that is often absent from religious strictures, many of which involve compiling lists of what is forbidden and dreaming up creatively horrendous punishments for those who fall short.

If Mr Grayling’s book is overly donnish, Frans de Waal’s is the opposite. A primatologist who has spent his career studying chimpanzees and bonobos, two of humanity’s closest living relatives, Mr de Waal draws on a lifetime of empirical research. His data provides plenty of evidence that religion is not necessary in order for animals to display something that looks strikingly like human morality.

Readers are told of chimps that, in lab tests, help other chimps obtain food even though there is no benefit in doing so, or even refusing rewards themselves until their troop-mates get some too. Powerful examples also come from the wild: young chimps fetch water for oldsters who cannot manage themselves, for instance, or adopt orphaned youngsters from other families. One troop of wild rhesus monkeys is even recorded as tolerating the serious social faux pas of a trisomic member—in other words, one with three copies of one chromosome, a condition that in humans is called Down’s syndrome.

Mr de Waal’s central concern is to attack the idea that what humans call morality stands apart from, and above, anything found in the “lower” animals. Most people, he notes, accept that their bodies evolved from those of man’s predecessors, but the conceits of religion and philosophy make it much harder to accept that the same is true of human minds and behaviour, no matter how good the evidence.

Human ethical codes, on this reading, arise from ancient social behaviours. Different versions of this can be found in a variety of animals, from chimps and bonobos to dogs. For Mr de Waal, religion is a natural consequence of combining the built-in behaviours of an intelligent, sociable ape with strong dominance hierarchies (God, on this reading, being the ultimate alpha male) and an unusually big brain, finely tuned to find patterns and assume cause and effect even when they are not actually there.

He has little patience for the sort of confident, assertive atheism championed by Mr Grayling, seeing it as tilting hopelessly against human nature. It is here that Mr de Waal’s book is at its weakest. His sophisticated interpretation of religion seems to make it hard for him to imagine that other people can take it literally. He compares the “neo-atheists” to people standing outside a cinema, earnestly pointing out that Leonardo DiCaprio did not really go down with the Titanic—in other words, a crowd of crashing bores spoiling the fun by stating the obvious to people who know better than to take a film as gospel truth. Mr de Waal has the more convincing argument, but Mr Grayling is the better rhetorician.