Research: Climate change helped elephants evolve a large brain
Nature & Science

Research: Climate change helped elephants evolve a large brain

Elephants have long captivated our attention, partly because of their sheer size and majesty. But we’re also struck by their complex behavior. In some ways, we’re fascinated because this behavior echoes our most humane feelings. For instance, elephants have repeatedly been observed using tools and grieving their dead.

Their evolutionary history is interesting, too. It parallels humans’ in many ways. Elephant ancestors originated in Africa, just like ours. Their descendants, among them mammoths, went out of Africa to inhabit other continents. And in the process they evolved the largest brain of any land animal. It weighs around 5kg, while our own brains weigh 1.4kg.

But what drove this particular element of elephant evolution? Even though the fossil record of elephant ancestors is rich – with almost 300 species described – we simply haven’t known the answer for a long time. From the earliest species with small brains to the modern elephants with large brains, there was an almost 30 million-year-long gap in our knowledge.

Now, thanks to cutting edge scanning techniques and state of the art statistical reconstruction of ancestral features, we have the answer. A team of scientists from South Africa, Europe and North America – including us – have spent six years reconstructing the first accurate time line of brain evolution in the elephant lineage. The results of this international collaboration have been published in Scientific Reports.

And the answer to this longstanding question? Climate change is a large part of it. A shift in climate, along with other environmental disruptions and the invasion of competitors and new predators all likely played an important role in reshaping ancient elephants’ brains. Knowing this not only solves a long standing scientific mystery. It also means we’ve got a way to understand how modern species might adapt to the current climate crisis.

Climate-linked changes

Our survey revealed that brain size in ancestral elephants increased in two pulses, approximately 26 and 20 million years ago. The encephalization quotient (a measure of relative brain size corrected for body size) doubled during each pulse. This transformed the small brain of early elephant relatives into a large brain comparable in every way to that of modern species.

Noticeably, these two pulses of growth in brain size correspond to periods of substantial environmental disruptions in Africa. Some 26 million years ago, Antarctica was frozen for the first time, which caused a global aridification of the climate. Africa’s dense rain forests turned into savannas and deserts.

The climate then changed again about 20 million years ago to revert to a warmer and wetter African environment. This climatic instability was supplemented by the appearance of a landbridge between Asia and Africa.

Before 20 million years ago, Africa was indeed an isolated continent. But because of continental drift it eventually collided with the Levant (the area encompassing modern day Palestine, Israel, Lebanon, Syria, Jordan and Iraq), enabling the invasion of rival he

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