Brains use up a lot of energy, and smaller brains use less energy. The externalization of knowledge in human societies, thus needing less energy to store a lot of information as individuals, may have favored a decrease in brain size.
Last year, a group of scientists made headlines when they concluded that the human brain shrank during the transition to modern urban societies about 3,000 years ago because, they said, our ancestors' ability to store information externally in social groups decreased our need to maintain large brains.
But since then, human brains have actually shrunk slightly. The lost volume, on average, would be roughly equivalent to that of four ping pong balls, says Jeremy DeSilva, an anthropologist at Dartmouth College in the US.
Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic.
As early humans faced new environmental challenges and evolved bigger bodies, they evolved larger and more complex brains. Large, complex brains can process and store a lot of information. That was a big advantage to early humans in their social interactions and encounters with unfamiliar habitats.
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We will likely live longer and become taller, as well as more lightly built. We'll probably be less aggressive and more agreeable, but have smaller brains. A bit like a golden retriever, we'll be friendly and jolly, but maybe not that interesting. At least, that's one possible future.
"Our ancestors had larger bodies than us, and needed larger brains to control and maintain those bodies," says Dr. Eiluned Pearce, a researcher in the Department of Experimental Psychology at Oxford, and coauthor of a 2013 paper on Neanderthal brains published in the Proceedings of the Royal Society B.
Neanderthals had bigger brains than people today. In any textbook on human evolution, you'll find that fact, often accompanied by measurements of endocranial volume, the space inside a skull. On average, this value is about 1410 cm3 (~6 cups) for Neanderthals and 1350 cm3 (5.7 cups) for recent humans.
Some of the shrinkage is very likely related to the decline in humans' average body size during the past 10,000 years. Brain size is scaled to body size because a larger body requires a larger nervous system to service it. As bodies became smaller, so did brains.
In healthy volunteers, total brain volume weakly correlates with intelligence, with a correlation value between 0.3 and 0.4 out of a possible 1.0. In other words, brain size accounts for between 9 and 16 percent of the overall variability in general intelligence.
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Broadly speaking, evolution simply means the gradual change in the genetics of a population over time. From that standpoint, human beings are constantly evolving and will continue to do so long as we continue to successfully reproduce.
Regular exercise can help protect the brain from shrinkage as people grow older. The Physical Activity Guidelines for Americans recommends that most people get a minimum of 150 minutes of heart rate-raising activity per week, along with a couple of days of some type of strength training.
“They were believed to be scavengers who made primitive tools and were incapable of language or symbolic thought.”Now, he says, researchers believe that Neanderthals “were highly intelligent, able to adapt to a wide variety of ecologicalzones, and capable of developing highly functional tools to help them do so.
Scientists have long known that our ability to think quickly and recall information, also known as fluid intelligence, peaks around age 20 and then begins a slow decline.
Scientists have concluded that Neanderthals were not the primitive dimwits they are commonly portrayed to have been.
The volume of the human brain has increased as humans have evolved (see Homininae), starting from about 600 cm3 in Homo habilis up to 1680 cm3 in Homo neanderthalensis, which was the hominid with the biggest brain size.
The most recent fossil and archaeological evidence of Neanderthals is from about 40,000 years ago in Europe. After that point they appear to have gone physically extinct, although part of them lives on in the DNA of humans alive today.
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According to the “cultural brain hypothesis,” humans evolved large brains and great intelligence in order to keep up with our complex social groups. We've always been a social species, and we may have developed our intelligence in part to maintain those relationships and function successfully in these environments.
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