Here's a small teaser to launch your Valentine's Day. What kind of book contains this steamy passage (and dozens of others like it?): "`Do it,' she said, without moving her body an inch. `Just do it'... In a daze - on automatic, but shaking with the urgency of it - he pulled up her dressing-gown to expose her naked buttocks. Plate still in her hand, she didn't move except to bend further forward over the sink..." And so on.

Could this be one of those naughty-but-quite-nice-really slices of soft porn that Virgin publishes under its Black Lace imprint? In fact, it appears in Baby Wars: parenthood and family strife (Fourth Estate, pounds 12.99), the second book in which evolutionary biologist Robin Baker dreams up saucy scenarios and then appends a po-faced Darwinian commentary to prove the size of his academic reputation. Co-authored with his partner, Elizabeth Oram, Baby Wars widens the scope of Baker's 1996 hit Sperm Wars to embrace cradle-to-grave episodes of family conflict, all designed to show that our drives and deeds are "orchestrated by genes, mediated by body chemistry" as we subconsciously aim at "reproductive success".

Fans will be glad to know that the imaginary Baker-Oram clans still find time for plenty of extra-curricular nookie as natural selection toils away in its unsleeping quest for healthy, high-status babies. Rather less amusingly, the little fables include scenes of incest and child abuse, also in that heavy-breathing style.

Baby Wars marks the absolute nadir of Trash Darwinism: clod-hopping accounts of living human beings as genetically-programmed automata. And Baker no longer has the academic standing to support his sledgehammer arguments. He quit Manchester University in 1996, referring to the "sudden disappearance" that left his students in the lurch.

Unlike its predecessor, Baby Wars doesn't primarily rest on Baker's original research. Its skimpy bibliography cites exactly 11 articles and 11 books not by its author. As for its endless sweeping obiter dicta, any moderately sceptical 16-year-old would want to challenge them. A few more titles of this calibre, and Fourth Estate's once-impeccable science list will be halfway down the road to astrology.

Yet the sheer tacky fatalism of the Baker-Oram world (like a Channel 5 daily soap crossed with Emmanuelle) does arouse a sort of hunger. It's a longing to return to all those cultural facets of affection and desire that mean nothing to the evolutionary Gradgrinds. To satisfy it (and for the ultimate literary Valentine) choose Norton's wonderful anthology The Book of Love (edited by Diane Ackerman and Jeanne Mackin, pounds 22.50): an 800-page feast of fiction, essays, letters, poetry and memoirs, with not a single selfish gene in sight.