If elephants never forget, the memories of mammoths need a little prompting. Nevertheless, inventive approaches to the extraction and sequencing of DNA from mammoths preserved in Siberian permafrost are allowing direct access to the deeper memories of elephant evolution.
There has been much debate about whether the woolly mammoth (Mammuthus primigenius) — that archetype of everything icy and Palaeolithic — was more closely related to the extant African or Asian elephant (Loxodonta africanus and Elephas maximus, respectively). Analysis of the complete mitochondrial genome of a mammoth by Hofreiter and colleagues (Nature 439, 724–727; (2006)) provides the answer: mammoths are more closely related to Asian elephants, but only just.
Current wisdom has it that the lineages leading to mammoths and both extant elephant species diverged about 6 million years ago in Africa. The new data suggest that the African lineage split first, followed around 440,000 years later by the separation between Asian elephants and mammoths.
Now that the phylogenetic relationships are slightly clearer, it would be interesting to discover how other extinct elephants fit into the picture. One thinks of elephants such as Anancus and Palaeoloxodon that foraged in temperate Europe during the Pleistocene — not to mention the mighty Mammuthus trogontherii, which at up to five metres tall was possibly the largest species of elephant ever, making the woolly mammoth look, if not dwarfed, then at least somewhat petite.
These questions may not be answered using ancient DNA, however. The permafrost environment seems to favour the preservation of ancient DNA in quantity, from mammoths as well as other species, as shown by Poinar and colleagues (Science 311, 392–394; 2006). But the likelihood of finding sufficiently informative DNA from species living outside the Arctic is almost certainly very much less. Yet, given the advances in sequencing ancient DNA (and, more importantly, verifying it), who knows? Perhaps there are still more mammoth memories to retrieve.