<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Roboto%3A300%2C400%2C500%2C700%7CRoboto+Slab%3A400%2C700">Baboons show climate change drove human origins - Filthy Monkey Men

Figuring out how our species evolved is hard. In fact, we’re not even sure where it happened. It turns out early Homo sapiens fossils are all diverse and messy, making it hard to figure out what’s going on. However, research on baboons may have the answer, revealing that this messiness might be the secret to our origins1.

Where early human fossils are found. They’re all over the place!

Baboons and climate change

Baboons are pretty awesome, especially if you’re interested in human evolution. They consist of multiple species that have been living in a variety of African environments for the past 2 million years. That’s almost as long as Homo has been kicking about there. As such, they provide a handy model for our evolution; tracking how different environments may have impacted our ancestors1.

The distribution of baboon species. The Xs mark where 2 species have met up and get frisky2, just like our ancestors did. Yet another reason baboons are awesome.

As such, a Desalegn Chala and a group of researchers from across Europe were curious about how all these baboons responded to the climate change that happened during this period. In particular, would they have seen their habitats expand or shrink as the environment changed1?

It turns out that this has happened a lot since the evolution of Homo. That entire period has fallen within the ice age, or Pleistocene. Whilst we often think of the ice age as a relatively recent super-cold snap with glaciers and mammoths, the phenomenon actually extends for the past 2.6 million years. Of course, the other wasn’t frozen over for that entire time. It alternated between warmer cycles (like now) and colder ones (like with the mammoths).

The cycles over the past 800,000 years. The last glacial maximum with Neanderthals and mammoths, which everyone thinks of as “the ice age”, is MIS 3

Modelling the baboon response

With this background in mind, Chala et al. began investigating what impact these climate cycles had on baboons. They built algorithms from where baboons live now to see what sorts of environments they like. These were then used to see how much of Africa would be suitable for each species during a cold snap and warmer period1.

All of this resulted in the map below, tracking changes between a warmer and colder period. As you might expect, the cold snaps saw good chunks of their territory becoming unsuitable for baboons (although did gain a few new areas). Overall, baboons would have lost ~14% of their territory during a cold period1.

Change in habitat suitability from warmer to colder periods. Blue are areas they could continue to live in, red is areas that would become unsuitable, and green are areas that would become suitable1.

Although that doesn’t sound like a lot, it becomes more extreme when you break it down by species. Some baboons lost nearly a quarter of their environment, whilst others gained 60%. Despite being a flexible group, it seems baboons were significantly impacted by climate change1.

This sort of isolation does more than change where baboons live. It can also impact their evolution. Groups could become isolated by these changing conditions, starting them down independent evolutionary paths. Then, when the climate changed back, these separate populations would meet back up and hybridise1.

Baboon groups may have become isolated by climate change (left) and then brought back together by more climate change (right), allowing for interbreeding and all sorts of fun stuff1.

Baboons explain human evolution

Of course, we don’t really care about baboons. We’re an egocentric species that want to understand our own origins. So what does this research teach us about that?

Well, it shows that humans may have still been influenced by climate change, despite our smarts. Just like us, baboons are supposed to be an adaptable bunch. However changing environments still had a big impact on their territory. As such, it would likely have been the same for our ancestors1.

Crucially, these changing conditions would have broken up early human populations. Fossils from early in the evolution of Homo sapiens show exceptional diversity. Could it be because of this repeated isolation drove different populations in different evolutionary directions?

So many early Homo sapiens skulls, so much variation3.

But perhaps most importantly, this breakup would have been temporary. Climates would shift again and these diverse populations would be smushed together. In the baboons, this interbreeding dramatically changed the genetic makeup of species, spreading distant genes all over the place. In fact, the resulting interbreeding even seems to have produced a whole new species: the kinda baboon2.

It’s pronounced “kindae” but I like the idea of it being just a kinda baboon. Pic by Kenneth Chiou – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=51738140

Perhaps our species has similar origins. We’re a weird hybrid, created by hybridisation between groups driven apart by climate change.

References

  1. Chala, D., Roos, C., Svenning, J.C. and Zinner, D., 2019. Species-specific effects of climate change on the distribution of suitable baboon habitats–Ecological niche modeling of current and Last Glacial Maximum conditions. Journal of human evolution132, pp.215-226.
  2. Rogers, J., Raveendran, M., Harris, R.A., Mailund, T., Leppälä, K., Athanasiadis, G., Schierup, M.H., Cheng, J., Munch, K., Walker, J.A. and Konkel, M.K., 2019. The comparative genomics and complex population history of Papio baboons. Science advances5(1), p.eaau6947.
  3. Stringer, C., 2016. The origin and evolution of Homo sapiens. Phil. Trans. R. Soc. B371(1698), p.20150237.

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