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Why is it that our Neanderthal ancestors never suffered from brain disorders like autism or schizophrenia but it's a common malice in the modern world? The reason is that our cave-dwelling ancestors didn't have the DNA triggers which can lead to these ailments. They were essentially turned off while the identical genes in today's humans are turned on. Alternatively, hundreds of other genes were turned 'on' in Neanderthals but are 'off' in people living today.
'The genes related to autism, as well as to schizophrenia and Alzheimer's disease, were more likely to be 'off' in Neanderthals than in modern humans,' said lead author Liram Carmel from Hebrew University of Jerusalem. The discovery underlines the power of the 'on/off' patterns.
'The 'on/off' switches could also explain the anatomical differences between archaic and present-day humans, including Neanderthals' shorter legs and arms, bow-leggedness, large hands and fingers, and curved arm bones,' Carmel explained. When dozens of brain-related genes became more active in today's humans, that produced the harmful side effect of neurological illnesses, the study noted. One person's genome can vary markedly from another's due to diet, environment and other factors.
'It is, therefore, impossible to know whether the 'on/off' patterns found in Neanderthal genes are typical of the species overall or peculiar to the individual studied, the study, published in the journal Science, concluded.
Of course, we've to take into account the fact that other than autism which is a developmental disorder (and any autistic child was far likelier to be cast aside rather than be taken care of), diseases like Alzheimer's and schizophrenia don't show up before the late 50s and 60s, an age our ancestors barely saw. There have also been other theories to try and explain why some ailments continue to persist in the modern day world, because they might well have given some of those members certain advantages over their counterparts.
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According to an article on Cracked, ailments like ADHD, Bipolar Disorder, OCD, Dyslexia and even autism would've actually given people suffering from them more advantages. Bipolar disorder for example would've been common for hunter-gatherers who would spend the summers stockpiling food and doing other such things and the cold winters in a semi-hibernation mode. Similarly, ADHD would allow hunter-gatherers to move on faster from one pasture to another before danger arrived and OCD would surely lead to a better immune system and hygiene levels which would allow the 'sufferers' to survive. And many suffering from some forms of autism usually exhibit skills in certain qualities which far exceeds those of the general population which would allow them to have an edge in certain activities.
Another theory by Andrew Miller, professor of psychiatry and behavioural sciences at Emory University, suggested that depression is a by-product of our ancestors' ability to fight infection.
'Most of the genetic variations that have been linked to depression turn out to affect the function of the immune system,' said Andrew Miller, professor of psychiatry and behavioural sciences at Emory University. 'This led us to rethink why depression seems to stay embedded in the genome,' added Miller, the journal Molecular Psychiatry reported. 'The basic idea is that depression and the genes that promote it were very adaptive for helping people especially young children not die of infection in the ancestral environment, even if those same behaviours are not helpful in our relationships with other people,' said Miller's colleague Charles Raison, from the University of Arizona.
Infection was the major cause of death in humans' early history, so surviving infection was a key determinant in whether someone was able to pass on his or her genes, said a university statement. Evolution and genetics have bound together depressive symptoms and bodily responses that were selected on the basis of reducing mortality from infection. Fever, fatigue/inactivity, social avoidance and anorexia can all be seen as adaptive behaviours in light of the need to contain infection, they study authors wrote. Similarly, a disruption of sleep patterns can be seen in both mood disorders and when the immune system is activated. This may come from our ancestors' need to stay on alert to fend off predators after injury, Miller said.
Read more about causes, symptoms, diagnosis and treatment of schizophrenia.
With inputs from IANS
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