There are two species of elephant - African and Asian - right? Wrong, say researchers studying elephants' DNA: Africa contains two species, one on the savannah, the other in the forests.

The species split shows that a single pan-African elephant conservation strategy would be misguided, say its advocates. Redefining the animal as two less populous species may also move the elephant up the endangered list.

Stephen O'Brien, of the National Cancer Institute (NCI) in Frederick, Maryland, and colleagues have drawn up a family tree on the basis of the sequences of four genes from tissue samples from 195 elephants in 21 populations across sub-Saharan Africa1.

Savannah elephants (Loxodonta africana africana) are in a separate branch of this tree to the smaller forest elephant (Loxodonta africana cyclotis), which has more rounded ears, a differently shaped head and smaller, downward-pointing tusks.

"The tree clearly shows a steep divergence between forest and savannah [elephants]," says team member Jill Pecon Slattery. Savannah elephants from Cameroon in west Africa, for example, are more closely related to those roaming South Africa's plains than to forest elephants from neighbouring Gabon.

The molecular survey confirms the conclusions of earlier work involving skull measurements. It "clinches things very decisively", says Colin Groves of the Australian National University in Canberra, one of the team that carried out the skull study.

Savannah elephants are far more genetically uniform than their forest counterparts, suggesting that they have passed through a genetic 'bottleneck', and that the present population is descended from just a few individuals. This may make them more susceptible to disease.

This bottleneck may have occurred when a few elephants seized an opportunity to expand across the savannah at roughly the end of the most recent ice age - the Pleistocene period - about 11,000 years ago. At this time, another elephant, Elephas iolensis, which until then seems to have dominated the grasslands, became extinct.

"Forest and savannah elephants must be managed separately," says Groves. What this means practically is yet to be decided, partly because little is known about forest elephants.

There are about 400,000 savannah elephants. Aerial censuses, dung counting and guesswork put numbers of the better-hidden forest elephants at between 50,000 and 100,000.

Forest elephants are under huge threatIan Douglas Hamilton, Save the Elephants

Rainforest fragmentation, ivory poaching and the bushmeat trade are all menacing forest elephants' seclusion. "They're under huge threat, and there's very little conservation effort," says Ian Douglas Hamilton, founder of Save the Elephants, a Nairobi-based conservation organization that is currently counting and radio-tracking forest elephants to develop a viable conservation strategy.

"The political implications [of reclassifying the elephant] are probably more important than the biological finding," says Douglas Hamilton. For example, the ivory trade might need to be regulated differently for each species. "We must carefully refine our techniques for identifying their tusks," agrees Groves.