How much does climate change drive evolution?

One of the major current topics I usually avoid is climate change. I’m so pessimistic about the chances that governments, which survive on corporate money, will take serious enough steps to lessen the impact of human industry and consumption on climate that I don’t like to dwell on the subject at any length.

It’s not that a groundswell of popular demand won’t eventually force corporations and their political minions to take climate change seriously. There’s no doubt that it will. It’s rather that I don’t believe that the groundswell will have effective force before the damage has been done, and to a far greater extent than we’re seeing already.

Popular media have done a fair  job (in a quantitative, not qualitative sense) of setting out the growing science on the physical changes that are occurring. We read every day about disappearing pack ice, about previously atypical droughts and floods, about ever more intense tropical storms and ever more frequent tornadoes. That almost as much has been reported of the scoffing reaction of the know-nothing climate change deniers as has been written about the real data is unfortunate, but it’s to be expected — and besides, as the evidence and the impact continue to pile up, fewer and fewer people will listen to an ever-dwindling number of naysayers.

But not enough real speculation (no, that’s not an oxymoron) has yet surfaced regarding the likely specific impacts of climate change on how a new environment may select new drivers for future evolution. There are several good reasons for this, including that we have trouble imagining ourselves living in ways dramatically different than we do now.

Another reason is that there’s much less direct scientific data with which to make predictions about environmental drivers of human evolution.

We have considerable data about how the climate changed in the past, but very little of that information is tied in any useful way to specifics about hominin, especially human, populations that may have lived through dramatic changes.

In fact, we have more direct information about how the Yucatan asteroid changed the climate 65,000,000 years ago and deselected the dinosaurs than we do about how spreading ice sheets affected early human groups in the recent past.

This knowledge gap is seldom noted in the general media, but it is widely understood by climate scientists, and it’s important enough to have been the subject of at least one major conference.

In 2010, the National Academy of Sciences published Understanding Climate’s Influence on Human Evolution, a report on the challenges facing climate scientists who are trying to understand the past influence of climate on the survival, distribution and evolution of early hominins — and hoping to use this information to give us a better idea of what we may face as the current climate shift intensifies.

We know that historical climate changes dramatically affected human settlement and dispersal patterns, but we know very little about how a changing climate may have acted as a driver in human evolutionary changes — as it were, shuffling the selection deck and sending our species off into new survival conditions, with different groups of winners and losers.

One dramatic depiction of the possibilities is Alice Roberts’s The Incredible Human Journey, first a book and later a five-part BBC series. Roberts supports the “out of Africa” theory of the dispersal of human populations. She makes a strong case that African homo species spread to Eurasia and later around the world thanks to a key episode of climate change.

During a crucial period of glaciation, about 100,000 years ago, sea levels dropped worldwide. One of the results was that the Red Sea gap between Africa and the Middle East shrank significantly. At the same time, lower sea levels meant that the fresh water outflows of Eurasian rivers, usually trapped below the lifeless desert above and flowing uselessly through underwater outlets, were accessible along the shoreline of the southeastern Arabian peninsula. According to Roberts, a combination of these lucky features enabled African humans to spread off the continent.

In the end, as we know, modern humans supplanted Neanderthals and Peking Man, dooming them to extinction and leaving us the dominant species. How different might this have been with a different climate history? Would we non-Africans all still be prehumans, the semi-intelligent pack animals — or food supply? — of advanced Africans who emerged only from their home continent tens of thousands of years later to subdue and dominate the rest of us?

Of course this is highly speculative, but you get the idea of how climate change might have equally dramatic effects this time around. Yet most of us ignore that part of the crisis. And one reason that we do is that there isn’t enough hard evidence that it’s happened before. Most of us are secure in the idea that we succeeded because we were somehow superior, more intelligent, more “worthy” of survival. What if the only reason we’re here is that we got the climate luck that the dinosaurs didn’t?

The climate scientists who wrote the NAS report know that these are important questions, and they recommend a number of practical steps that would improve both their science and the relevance of that science to the debate about public policy.

The report states that “although we have a broad understanding of African and Eurasian climate history, this climate record generally lacks the temporal resolution and details of rainfall and temperature that potentially impacted how the hominins lived, and in particular does not adequately reflect differences in past climates between regions.” The existing climate record also contains “substantial temporal gaps.” While “a general understanding of the timing of major events in human evolution exists, … our ability to interpret what has driven these events remains limited by a paucity of fossil material, particularly over the most interesting periods of rapid evolutionary change.”

 The report suggests two major research themes to address the problem. First, determine “the impacts of climate change and climate variability on human evolution and dispersal.” The report explains that “hypotheses linking climate change and hominin evolution are based on indications that large-scale shifts in climate or climate variability altered the landscape ecology which, in turn, presented specific adaptive or speciation pressures that led to genetic selection and innovation.”

The second theme is “integrating climate modeling, environmental records, and biotic responses.” The aim is to “define the physical and biotic mechanisms whereby past environmental changes may have produced evolutionary (and behavioral) responses in fossil hominins.”

Maybe, if all of us — corporatists and Bible literalists and governments included — are shown the ways that climate change can alter not just the lives of some people but the future of all people, just maybe we’ll act in time.

I’m not holding my breath — although in a few decades, if there’s not enough dramatic change, everyone will be doing just that.


One thought on “How much does climate change drive evolution?

  1. The point being to create one more trigger for action since the actual long term effects on evolution are insignificant to us short termists, and that includes not just politicians miniscule attention spans, compared to the disaster which must come before environmentally caused evolution change. That suggests details of the disaster facing us, or more likely our grandchildren
    will be the most effective push to action.

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