Climate change human evolution are linked.
This connection makes sense because climate change is, and always has been, an important driver of evolution.
Change in environmental conditions at any one place creates disturbance that forces innovation on the organisms that live there. All that is required is for the disturbance to be outside the norm.
When changes to conditions under harsh, intense or extensive, the natural tolerances of plants, animals and microbes are pushed to the limit.
When disturbance is severe one of three things happens, organisms can
We tend to think of the first of these, adaptation, as being genetic. Natural selection weeding out the least well suited to the conditions. And this is what happens over time.
But organisms can also 'adapt' to environmental change through flexible behaviours and physiologies - the technical term is phenotypic plasticity.
So it is possible for organisms to survive climate change without the need for genetic change so long as they are flexible enough or already have a wide tolerance.
When adaptation or flexibility is not possible, organisms can move to find conditions that they can tolerate.
Moving is easy enough if you are an animal or a microbe spreading on the wind. It is harder for plants that for anything greater than a few feet can only 'move' between generations by spreading seed.
Moving also assumes that there is somewhere suitable to go. Even mobile species specialised for mountain tops have nowhere to go if the snowline creeps upward.
This leaves the last option, extinction.
Humans have so far avoided option 3 because we became very good indeed at adaptation. We evolved the flexibility to cope with life on the savannas. Gathering, hunting and avoiding other hunters for 3 million years.
As a medium sized bipedal mammal, bite sized and not especially fleet of foot, this was a good effort.
There is a climate change human evolution theory that climate change was a trigger that prompted the development of an upright stance and walking on two-legs that we understand as so obviously human.
A change to a drier climate in the rift valley of Africa produced a shift in vegetation from forest to savanna.
Primarily tree dwelling primates now spent more time on the ground as this was where there was more food to be had. An upright posture made hunting and gathering more efficient together with loss of hair and evolution of sweat glands to cope with the heat out in the open.
The idea was not that upright was fast or stronger posture [it isn't compared to big cats] but it did allow for endurance.
Few animals can run for a long time, especially antelope who escaped predators with agility and a burst of extreme speed. If you can stay close enough to see where they go [easier on the open savannas than in the forest] and keep chasing them, they soon tire and collapse of exhaustion.
Upright walking and jogging is a highly energy efficient way to cover a lot of ground with minimal effort. It must have compensated hugely for a relative lack of strength and agility so obvious in the other predators.
And it worked, but only after climate change had dried and opened up the vegetation.
Then, all of a sudden, humans decided to move. [Or perhaps they had always moved but couldn't get far because crossing expanses of water was beyond them].
Climate change was needed to provide a land bridge from Africa to the middle-east and everything beyond allowing humans to diffuse away from the savannas and into a wide range of new habitats beyond.
There were still humans on the savannas of course, only now they were also on their way to other parts of the world.
And adaptability allowed them to survive when they got there.
Once this so-called 'great leap forward' started, the rate of expansion [diffusion is probably a better description] was quite rapid and yet there were no humans in the Americas before 13,000 years ago, none in Australia until 42,000 or in New Zealand until 1,000 years ago.
Homo sapiens essentially ignored climate change. They were too busy taking over the world.
Climate change facilitated human movements as land bridges were created from global sea level changes and would certainly created local disturbance that would have prompted people to move on.
So climate change human evolution would have seen local consequences in the last 50,000 years as the expansion across the globe was completed, especially where climate affected the availability of local resources and helped drive movement.
In more recent times since the invention of agriculture some 10,000 years ago, climate change effects on agriculture have often caused major social disruption including the collapse of civilisations and cultures.
It is too early to know what will happen to climate change human evolution now that we are so numerous and appear to ignore all the normal rules of nature.
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