Climate change made humans successful

Humans have absurdly large brains. It takes almost 1/5 of our daily calories1 (the equivalent of a big mac) just to keep it running; but the benefits of having such a large brain are fairly obvious. They’re the reason we got to be so successful. But faced with these side-effects, it’s certainly puzzling how we managed to evolve them in the first place, particularly given every other species ever seems to get by just fine without them.

A human and chimp brain. As you can see, when I say ours are absurdly large, I mean it

A human and chimp brain. As you can see, when I say ours are absurdly large, I mean it

One of my favourite explanations is that we can blame climate change for our intelligence (and then, millions of years later, we can blame our intelligence for climate change). Imagine a dry climate. Obviously you’d need a special set of strategies, tools and behaviours to survive. Similarily, in a wet environment you’d need another unique set of adaptations. But what if the climate kept changing, swinging between wet and dry? The group that could innovate and adapt rapidly would win out; and that’s what our big brains let us do. We’re successful because no matter what the planet throws at us, we have the brains to figure out how to survive. And sure enough, palaeoclimate data shows there was a period of extreme climate variability, around 1 – 2 million years ago when our brains started to get big2.

However, Dr Grove – one of the lead proponents of this theory – reckons that this can also explain parts of our geography as well as our biology3. You see, modern humans evolved in Africa around 195,000 years ago4 and began expanding out into the rest of the world around 100,000 years ago. Dr Grove reckoned that a period of climate change forced our ancestors to become more flexible, allowing them to begin this migration; explaining why we suddenly got our act together and left home after 95,000 years of living in our parents basement.

When and where we migrated, along with what species of human were already living there when we arrived

When and where we migrated, along with what species of human were already living there when we arrived

To investigate this he created a computer model for how much climate variation is needed to favour flexibility. He discovered that the key was not necessarily severe climate change but repeated climate change. A lot of small changes were more likely to result in flexible computer-animals than a couple of big changes. Having run this model a few times and identified the factors that result in the evolution of flexibility he looked for these factors in sediment cores from Lake Tana3.

These are layers of sediment deposited on the lake bed at a fairly regular basis, each containing some elements from the air present in the period they were deposited. These elements correlate with the climate (in this case the ratio of titanium and calcium reflects the amount of rain during the period). As such they’re a very neat weather log of the planet over the past few hundred thousand years. When applying his climate model to it, Dr Grove found that there was a period leading up to 100,000 years ago when rainfall fluctuated a lot; which would have forced our ancestors to develop more flexible behaviour. This, you may, recall lines up nicely with around the time humans began leaving Africa3.

The element ratios from Lake Tana (correlating with levels of more/less rainfall) were incredibly variable leading up to the human migrations out of Africa (brown bands)

The element ratios from Lake Tana (correlating with levels of more/less rainfall) were incredibly variable leading up to the human migrations out of Africa (brown bands)

This vindicates Dr Grove’s predictions very nicely; strongly suggesting he’s right.  It seems that the environment began fluctuating around 150,000 years ago; forcing our ancestors to develop more flexible strategies that allowed them to survive in any climate. And then they realised “hey, the rest of the world counts as ‘any climate'” so off they went; migrating throughout the rest of the world. And it seems pretty good that they did have this added flexibility because boy, did they encounter a lot of different things. From ice ages to Neanderthals, our flexibility was pushed to the limit.

It should be noted that this research was only looking at one aspect of the climate (rain) from one region, so a larger comparison should be done to fully confirm his findings; although the strength of this result suggests that any such investigation will still vindicate these results.


  1. Brady, S., Siegel, G., Albers, R. W., & Price, D. (Eds.). (2005). Basic neurochemistry: molecular, cellular and medical aspects. Academic Press.
  2. Grove, M. (2012). Orbital dynamics, environmental heterogeneity, and the evolution of the human brain. Intelligence, 40(5), 404-418.
  3. Grove, M. (2014). Palaeoclimates, plasticity, and the early dispersal of< i> Homo sapiens</i>. Quaternary International.
  4. Boyd and Silk (2012). How Humans Evolved.

9 thoughts on “Climate change made humans successful

  1. It makes sense. Rapid change seems to foster some kinds of mind development. I’ve made a point of using fast-moving games with puppies, and that’s seemed to result in clever adult dogs (although the N is extremely small, and I have no control group).

    I’ve wondered about the pace of modern life. I’m sometimes amazed at how quick information is these days (how rapidly some speak, how quickly info flashes on the TV), and I’ve wondered if being raised in that atmosphere makes it seem normal. Back when trains and planes were first becoming a thing, people then worried if traveling at speeds of [gasp] 30-40 MPH might not have horrible effects on people.

    • I’d like to imagine a prehistoric wise woman once sat down and had a vision of McDonalds.

      “They will make circular meat, and put it between circular bread”
      “What is bread o wise woman”
      “I do not know, but one day someone will slice it and that will be the best thing ever”

  2. Is this research implying that once sapiens adapted to a dry spell, then adapted to a wet spell and
    then had to adapt to a dry spell again, the second adaption to a dry spell made him more clever
    than the first time ?

    What about him them moving through dry and wet, dry and wet areas as he moved out of Africa then?
    I am going to go for it now.

    Mentioned previously; A human has 1 billion sells in his body and a 100 billion microbes living in and
    on it. Apparently the vessels of ones upper colon is similar to that of the brain. Apparently, when
    the vessels of the upper colon deteriorates, one tends to acquire Parkinson and or Alzheimer’s. The
    chimps colon and ours are vastly different. Secondary effect of “climate change” ?

    Still cannot see how all this brought us where we are today. Brain wise. According to a specialist
    I read on lately, sapiens could only have developed “real” consciousness approximately 10,000
    years ago. To make you capable of thinking about what you are thinking. Also makes me wonder
    about the new earth philosophy. Maybe they are not as nuts as one thinks but have their facts
    jumbled up.

    Oh dear. A terrible thought !

  3. Of course climate change must have had some effects on human evolution over the last 5 million years. In addition there appear to have been some significant changes since Homo sapiens appeared on the scene some 200,000 years ago. But is it really necessary to relate the apparent surge in human intelligence to climate change. Even if the surge occurred at about the same time, it may be that the “great leap forward” was inevitable because of the way we were evolving and the timing coincidental.
    I ask because I have been looking at how the evolution of language, seen as a cultural tool, could trigger a very rapid change in both language skills and perceived intelligence – see How Humans invented Natural Language and why Animals don’t have it ( It seems that there is a tipping point in the way the animal brain works which means that once a species has discovered a way to pass sufficient information to its infants this tipping point is reached and the flood gates open. A small increase in the power of the initially primitive language means that the species can learn to make more powerful tools. And as language is a tool it can learn, generation by generation, to develop a more powerful language. And one of the effects of using a more powerful language for teaching is that you can pack knowledge more effectively into the brain. This means that there is room to learn more and more, generation by generation, without any sign of the brain getting bigger.

    However before the tipping point is reached a species which needs to pack more knowledge into its brain will need a bigger and more expensive brain, and the tipping point is so high that only Homo Sapiens has succeeded in reaching it and storming through to intelligence and linguistic pastures new on the other side.

    It seems to me that other people have not thoroughly investigated the tipping point possibility when you have a primitive language which is used to pass tool-making tool-making knowledge to the next generation. (Am I right or have I missed an important reference that blows the idea out of the water?)

  4. There is a great book on a much earlier version of this topic called Children of the Ice Age by Steven Stanley. The children are us in our Australopithecine stage, evolving in the tropics of Africa which were climate-changing at the time from rain forest to savannah.

    • That argument has always struck me as a bit iffy, given that we’ve found early hominins in a myriad of environments. From tropical forests to swamps to Savannah to deserts. It doesn’t seem like there was a single environmental trend forcing us in a particular direction (e.g. to adapt to the Savannah). Instead, it almost looks like we were evolving to just do well in a broad range of environments. Bipedalism is one of the most versatile ways of moving. With it we can move quickly in almost any environment.

      • We know that human groups as far apart, in evolutionary terms, as Neanderthals and Denisovans, could interbreed, and presumably this was not a unique event, but various groups have been separating into different evolutionary niches, and evolving to suit their particular niche for millions of years. One group of hunters using simple stone weapons may evolve better hands which enable them to make better tools while another group living by the sea and diving for shell fish might evolve better lungs and loose body hair.

        As the climate changes the various evolutionary niche grow or shrink, and in some places new niches will appear and old niches will disappear. This will encourage population movements and groups which may have been separate for many tens or hundreds of thousand years to meet and interbreed – and their most successful offspring may well end up with the “best” improvements of both lines of ancestors. If we think of climates switching at say 200,000 year intervals that is 20 “evolve a bit and then reshuffle the pack of genes in 4 million years– a real cauldron for rapid evolution of desirable features.

        In such circumstance it would be wrong to associate the changes to any one climate change episode, but rather to the fact of climate instability over several million years.

        • Its certainly interesting to ask “are humans/neanderthals/denisovans unique in terms of interbreeding; or do we just think they are because we only have their genome”. If we ever found an erectus/ergaster and heidelbergensis genome etc., would we find similar evidence? Or is getting funky with other species something only more modern hominins do?

          I think we might see that sort of evidence in older species, given that really old mtDNA from spain shows some sign of it

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