Did Neanderthals get depressed? (12/27/10)
The Four Different Kinds of Human
It’s not every year you recognize four different human proto-species were operating at the same time – and relatively recently. What’s even stranger is that we still carry many of their genes.
In neurological terms, these groups were close – really close. That fact may help explain what keeps brains operating among us and the animals with which we share this planet.
Of the four human groups, none of us have met a Flores islander, who appear to be have been Hobbit sized, died out perhaps twelve to eighteen thousand years ago and had a brain pan the size of a chimpanzee. Most of us recognize Neanderthals from books and movies set 40,000 years before Hollywood, though some would argue they continue to play a role in political life.
But Denisovans? We’re related to a whole new proto-species of cave men from Siberia?
As it turns out, quite a few of us are.
Rise of the Denisovans
Svante Paabo of the Max Planck Institute has had a lot of fun rewriting human genetics. Not everyone agrees with his work, but new sequencing of a tooth and a finger bone from the Denisova cave in southern Siberian have delineated a new group of humans who were around when we, home sapiens, moved out of Africa 50,000 or so years ago. To Paabo, the Neanderthals were the western Eurasian group that greeted traveling home sapiens, the Denisovans, yet more distantly related, the eastern Eurasian group that met modern humans.
And they interbred.
About 4-6% of human genes from Melanesians appear to be of Denisovan origin. So DNA from Denisovans, as well as DNA from Neanderthals, is still around on the earth – inside us.
Many other old bits and pieces are hanging around inside our genomes. After all, at least 8% of our DNA is derived from retroviruses. But some parts of that DNA involve information molecules necessary to what we consider our selfhood and individuality.
The Brain’s Information Processing Machinery
Using very similar kinds of genetic analysis, Seth Grant of Edinburgh University and the Sanger Institute decided to look at human nerve cell DNA. Getting fresh brain cell material is difficult. All the nerve cells came direct from neurological surgery – humans are notoriously uncomfortable having biopsies clipped inside their heads.
Grant was interested in the proteins that lie within the Post-Synaptic Density – the big bunch of proteins and stuff that lives at the end of the business end of nerve cells.
Nerve cells do, in much more modulated ways, what computer chips do – they fire or don’t fire. When they fire, they turn on a whole series of different proteins that then spread information through the next cell – the PSD.
Grant found 1461 PSD proteins. Many were related to major human neurological problems, like Alzheimer’s and learning disabilities. The weird part was how well PSD proteins were preserved throughout the evolutionary tree.
Generally, genes change a lot over time. Genes that seem to be particularly important to function, like energy metabolism, change very little. Whether it’s because they’re already perfected or so necessary to normal survival is not always clear.
The PSD genes were remarkably preserved throughout evolution. Go to a rat, or a mouse, a Neanderthal, or a present day human, and that integrated group of nerve cell proteins looks pretty much the same.
What are they doing? Information processing. Some PSD proteins are helping send information everywhere in the cell, while others appear to be placing down the anatomic basis of memory.
Memory, like all information, is physical.
Professor Grant was sufficiently impressed by the remarkable similarity of animal neurological machinery that he remarked to the NY Times that Neanderthals “would have suffered from the same range of psychiatric disease as humans.”
Depression, as do most human diseases, almost always involves complex environmental factors. We can make rats and mice look “depressed” through the environmental manipulation of learned helplessness, where no matter what the rat does it can’t succeed, as when it’s stuck on a tiny island where it’s constantly and continuously drowned.
Yet even in if “Jurassic Park” style we cloned a Neanderthal, we would know little of Neanderthal society, its communications, or its sense of meaning. That makes it difficult to verify the psychiatric problems of 40,000 years ago.
What we can verify is how similar our neurological machinery is from animal to animal. We can verify that our post-synaptic nerve cell machinery is critically important and critically preserved throughout evolution. We can also verify that much of that information processing seems to go awry, often in very similar ways, in illnesses we consider symptomatically to be different – like learning disabilities and depression.
So again we find kinship in the strangest places – between Siberian cave dwellers, mice, rats, and the people of today. And it’s all around not just genes but genes that specify proteins that help determine how information is collected, communicated, remembered and forgotten – the information that makes all of us us.
That’s the same information we use to rebuild ourselves anew each hour and day, the information we process so that we can learn and continuously adapt to our environment.
And if we give our bodies the right kind of information they can stay healthy. And lifestyle is a huge part of providing the right kind of information, the information that allows our bodies to regenerate and renew themselves, what makes us more youthful and alive.
Those genes need the right kind of environment to get on well. You can help provide the proper environment – if you know the way of rest. It’s all about rebuilding your body the way it’s built.
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