Are we evolving? - June 2010 was the hottest June on record (since NOAA began keeping track of temperatures in 1880). Climate change may not be good for current humans, but it may have helped our ancestors BECOME human--are we still evolving? In the Turkana Basin of Kenya, one of the places where human life began, the average daily temperature has reached the mid-90s or higher, year-round, for the past 4 million years. But it was the altitude, not the heat, that forced ancient Tibetans to undergo the fastest evolution ever seen in humans.
The need to stay cool in that cradle of human evolution may relate, at least in part, to why pre-humans learned to walk upright, lost the fur that covered the bodies of their predecessors and became able to sweat more. Earth scientist Benjamin Passey says, "This region, which is one of the key places where fossils have been found documenting human evolution, has been a really hot place for a really long time, even during the period between 3 million years ago and now when the ice ages began and the global climate became cooler." This is the "thermal hypothesis" of human evolution.
This hypothesis states that our pre-human ancestors gained an evolutionary advantage in walking upright because doing so was cooler (when it is sunny, the near-surface air is warmer than air a few feet above the ground) and exposed their body mass to less sunlight than did crawling on all fours. The loss of body hair (fur) and the ability to regulate body temperature through perspiration would have been other adaptations helpful for living in a warm climate, according to the hypothesis.
Passey says, "In order to figure out if (the thermal hypothesis) is possibly true or not, we have to know whether it was actually hot when and where these beings were evolving. If it was hot, then that hypothesis is credible. If it was not, then we can throw out the hypothesis."
Evaluating whether the ancient Turkana Basin climate was, in fact, the same scorching place it is today has been difficult up until now because there are very few direct ways of determining ancient temperature, but Passey's team developed a method that involves determining the temperatures of carbonate minerals that form naturally in soil by examining "clumps" of rare isotopes. In the case of soil carbonates common in the Turkana Basin, these tests told the team that average soil temperatures were between 86 and 95 degrees Fahrenheit, meaning that average daytime air temperatures were even higher.
According to passey, "We already have evidence that habitats in ancient East Africa were becoming more open, which is also hypothetically part of the scenario for the development of bipedalism and other human evolution, but now we have evidence that it was hot."In more recent history, Tibetans split off from their Han Chinese ancestors about 2,750 years ago, but only the ones whose lungs could evolve to function at high altitudes survived when they moved to the Tibetan Plateau. This rapid change took place in a single gene which helps to regulate the body's response to a low-oxygen environment.In LiveScience.com, Jeremy Hsu quotes evolutionary biologist Rasmus Nielsen as saying, ""If we go to high altitude, we produce more hemoglobin, but there's a cost to that. Tibetans can perform even better without the extra hemoglobin. It took only a few hundred generations to change the [gene] frequency, which can only happen if a lot of people have died. In that sense, it must have had a strong effect on fitness."
Let's just hope that climate change doesn't mean we're going to evolve even more: We may need it, but it's a tough way to get it.
Are we STILL evolving? Anne Strieber thinks we are and she's figured out WHY, HOW and WHO is helping us to do it, and she explains it just for our subscribers!
To learn more, click here, here and here.
Art credit: Dreamstime.com
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