How did elephants evolve such a large brain? Climate change is part of the answer
Elephants have long captivated our attention, partly because of their sheer size and majesty. But we’re also struck by their complex behaviour. In some ways, we’re fascinated because this behaviour 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 5 kg, while our own brains weigh 1.4 kg.
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.
Our survey revealed that brain size in ancestral elephants increased in two pulses, approximately 26 and 20 million years ago. The encephalisation 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 herbivores and new predators from Asia. The invasive fauna included the ancestors of modern-day lion, zebra, rhinoceros, hippopotamus and antelopes. The Great Apes did not exist yet. Some large species died out during this time; the most famous is Arsinoitherium, a rhino-like relative of elephants.
Read the full article here: Down to Earth