Darwin in Malibu, Hampstead Theatre, London

On the sun-kissed deck of a Malibu beach house, Charles Darwin (Oliver Ford Davies) is knocking back banana milk shakes, tucking into a fat "fuck-a-page sandbuster" by Pat Booth and enjoying the attentions of a gorgeous blonde Californian girl (Cressida Whyte). Considering it's 145 years since he published On the Origin of Species and 122 years since his death, it can't be considered a wholly lamentable fate.

But then Darwin's peace is disturbed by the arrival of two contemporaries who take diametrically opposed positions on his work. There's his vociferous champion Thomas Huxley (Douglas Henshall), who once declared publicly that he would rather be descended from an ape than a bishop, and his sanctimonious, God-botherer adversary Samuel Wilberforce, Bishop of Oxford (Nigel Planer), who thinks that they are all in purgatory and his only chance of getting to heaven lies in converting the other two to his creationist convictions.

At first, it's easy to underestimate Crispin Whittell's agile, witty play. Even in Robert Delamere's luxuriously cast and expertly acted production, the early scenes suggest that we're in for a kind of middlebrow intellectual sitcom based on the incongruity of Victorian thinkers evolving (and refusing to evolve) in La-la-land. "Who needs evolution when you have plastic surgery?" Darwin asks.

The brainy slapstick continues throughout and produces some very funny set pieces and running gags. There's the delicious sight of Darwin poring over horoscopes in a glossy mag, and his skirmish with Wilberforce over the contradictions in any concept of heaven. (How could he be allowed to indulge his passion for shooting partridges there, given that the birds would, by definition, have to be virtuous partridges who deserve a better reward than being blasted to bits by him?)

But gradually, Whittell's drama deepens and begins to use its posthumous perspective on existence more in the manner of Michael Frayn's Copenhagen. If the latter employed the afterlife as an arena for meditating on the mysteries of human motivation, Darwin in Malibu (whose four characters have all been bereaved in painful circumstances) is well positioned to explore what follows from the fact that man is the only creature who lives his life conscious of his own mortality. I am sure that evolutionary psychology must have worked out how that sobering knowledge fits usefully into the Darwinian scheme, but Whittell's Darwin seems to intimate that this human development gave rise to the undying need for a faith that cannot quite be reconciled with his system.

Such reflections throw welcome shadows over the sun-baked scene. Though there were aspects of the play I didn't care for, I ended up feeling that Whittell is a dramatist who is clever enough to know that cleverness is not enough, and to act accordingly.

To 16 October (020-7722 9301)