Youth and the Pleistocene Climate
At the recent UN climate meetings, youth activists once again figured prominently. Over the last few years, public discussion of climate change has benefited enormously from their passion and sense of urgency. It’s understandable that young people feel so strongly — after all its their future that’s on the line. But this is actually not the first time that humans have confronted severe environmental changes, and those earlier episodes have a special connection with adolescence itself.
While climate in the past has always been variable, there was a period in the Pleistocene starting around 700,000 years ago when the magnitude of this variation was especially large. This led to dramatic changes in average temperature, in some cases 5–10 °C in less than a hundred years.
Changes in temperature in turn have a huge impact on land types and habitats. (This is what’s so alarming about human induced climate change). At one end of the Pleistocene spectrum there were cold and dry glacial conditions with less forest and more extreme desert. In these conditions, the northern forests that exist today were gone, replaced by ice and tundra. At the other end of the spectrum, interglacial periods could be warmer and wetter than today’s earth. (At one point the Sahara was actually a grassland).
Sudden changes between extremes like these had a massive impact on organisms living at the time. Our own ancestors were confronted with this unpredictable world — frequent changes in the habitats around them necessitated frequent updates in their approach to survival. Because of this, climate variability is seen by many as a driving force in human evolution.
One change connected with it is the evolution of a larger brain. Big brains enabled our ancestors to be more flexible and adaptable. They acquired more complex hunting and foraging strategies, and crucially had the ability to adapt and come up with new ones when needed. (It is ironic that eventually one of those new strategies involved the burning of fossil fuels).
Other changes involved differences in our life history, one of which is an extended juvenile period and adolescence. Humans become reproductively active significantly later than closely related primates. A chimpanzee female starts reproducing at about 13 years of age on average. For humans this is much later, in the late teens for women in traditional societies. (And later still in modern society). The human life cycle includes an extended juvenile period before puberty, and also an extended period after puberty when humans become sexually mature, but are not yet fully adult. The latter period, adolescence, is thought by many to be a unique human evolutionary innovation.
Adolescence has several connections to climate variability. One is through its association with the evolution of large brains. Adolescents are learning the many economic, social and cultural details they need to be effective adults. In that sense they are completing the process of building an adult brain. But they do more than just absorb the wisdom of their elders. Part of what was required of humans facing an uncertain Pleistocene environment was to change and adapt, creating new survival strategies when needed. Many of the characteristics of adolescents seem well-tailored to solve this type of problem. These include an ability to think outside the box, a desire to test themselves, a willingness to do hard work, and as parents well know, a tendency to push boundaries.
Today we find ourselves entering another period of intense climate change, this time caused by our own activities. Let us hope that the energy and fresh thinking of young people can once again help us through it.
