Human Population Growth and Evolution

From Daily Galaxy: Hyper Evolution -- Human Population Growth is Accelerating Species Change

In a fascinating discovery that counters a common theory that human evolution has slowed to a crawl or even stopped in modern humans, a study examining data from an international genomics project describes the past 40,000 years as a time of supercharged evolutionary change, driven by exponential population growth and cultural shifts.
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A team led by University of Wisconsin-Madison anthropologist John Hawks estimated that positive selection just in the past 5,000 years alone -- dating back to the Stone Age -- has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations.
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In a fascinating discovery that counters a common theory that human evolution has slowed to a crawl or even stopped in modern humans, a study examining data from an international genomics project describes the past 40,000 years as a time of supercharged evolutionary change, driven by exponential population growth and cultural shifts.
...
A team led by University of Wisconsin-Madison anthropologist John Hawks estimated that positive selection just in the past 5,000 years alone -- dating back to the Stone Age -- has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations.
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The human population has grown from a few million people 10,000 years ago to about 200 million people at A.D. 0, to 600 million people in the year 1700, to more than 6.5 billion today. Prior to these times, the population was so small for so long that positive selection occurred at a glacial pace, Hawks says.

"What's really amazing about humans," Hawks continued, "that is not true with most other species, is that for a long time we were just a little ape species in one corner of Africa, and weren't genetically sampling anything like the potential we have now."

"Five thousand years is such a small sliver of time -- it's 100 to 200 generations ago. That's how long it's been since some of these genes originated, and today they are in 30 or 40 percent of people because they've had such an advantage. It's like 'invasion of the body snatchers.'"

What drives the pace of evolution? Strong, and relatively rapidly changing environmental factors that will heavily benefit one genetic group over another. Speciation is driven by having isolated groups, but evolutionary change within a species is driven by having a large population size, with good communications to propagate advantageous mutations to a large part of the population.

Even non-beneficial mutations can propagate rapidly under those conditions, as long as they confer no disadvantage: Consider, 12,000 years ago, no-one had blue eyes - and apart from a few in one corner of the world, no-one could digest raw milk after childhood.

Of course, change isn't always advancement.