Alzheimer’s origins tied to rise of human intelligence

May 27, 2015

Image: Mahmoud Zayat/AFP/Getty

By Nala Rogers

Alzheimer’s disease may have evolved alongside human intelligence, researchers report in a paper posted this month on BioRxiv1.

The study finds evidence that 50,000 to 200,000 years ago, natural selection drove changes in six genes involved in brain development. This may have helped to increase the connectivity of neurons, making modern humans smarter as they evolved from their hominin ancestors. But that new intellectual capacity was not without cost: the same genes are implicated in Alzheimer’s disease.

Kun Tang, a population geneticist at the Shanghai Institutes for Biological Sciences in China who led the research, speculates that the memory disorder developed as ageing brains struggled with new metabolic demands imposed by increasing intelligence. Humans are the only species known to develop Alzheimer’s; the disease is absent even in closely related primate species such as chimpanzees.


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15 comments on “Alzheimer’s origins tied to rise of human intelligence

  • Darn! So that is both schizophrenia and alzheimers the price to pay for the cortical hominin upgrade.

    Worth it though…

    Lets try and fix schizophrenia and alzheimers without rolling back the upgrade.



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  • This is the way science roles; no matter how stark, unwelcome or frightening, it tells the truth.

    Further to which, if or when at any time accepted findings are found to be at fault, it self-corrects by means of its intrinsic processes.

    In other words, if conducted with integrity, science works.



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  • I can’t help but favor the hypothesis that as a chemical machine, it must be possible to alter the disease process at some point that will be beneficial to the individual, especially during the final stages of the life cycle. Of course, it’s quite likely that the complexity of the systems will contravene even our most clever attempts, but I can’t believe that until it’s been proven to be so.

    What a wonderful time to be alive, with all the vistas of knowledge so newly opened before us. Even if we appear to be losing ground to vicious and homicidal theists, we are left with so many uncertainties with which to joust.



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  • In our past anything terrible that happened to you after age 30 was worth it. I seem to recall the average life span of Romans was 25. Of course that includes many who die in infancy and childhood.



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  • Of course Kevin, the corollory of self-correction is refinement.

    And yes, ‘rolls’ on; if I’d paid proper attention in Latin classes I’d be able spell properly; mind you, I was only about nine or ten years of age at the time, and I finally got expelled anyway; been duckin’ and divin’ ever since.



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  • My sentiment entirely Charles.

    It’s tragic that so few people are aware of the fact; I think that were they to be so, superstition would have far less impact as a controlling factor in the lives of hundreds of billions of individuals.

    What a shame the human intellect has been so cruelly hijacketed.



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  • How would we ever know if another species had Alzheimer’s sufferers, I mean our communication channels even with our closest cousins are pretty rudimentary and Noam Chimpsky’s seem to be a minority chimpanzee population. Maybe all the dumber chimps are suffering from AD?
    My dog now aged 14 seems dafter than when he was younger. Maybe wild animals are no longer “fit” enough to survive the onset of AD?



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  • “how would we know ? Alzheimer’s is easy to physically identify in a dissected or scanned brain.”

    Yes, but has anyone ever bothered to do it on a non-human?

    One assumes they did for Mad Cow Disease but animal autopsies are rare unless there is a suspected association with a human death



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  • Dogs can get a condition called cognitive dysfunction which is very similar to Alzheimer’s disease in human beings. Both are likely caused by oxidative stress. The challenge is to find the right combination and concentrations of antioxidants to treat both diseases.

    http://www.drsfostersmith.com/pic/article.cfm?articleid=1346

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2390776/

    http://onlinelibrary.wiley.com/doi/10.1111/j.1479-8301.2009.00299.x/full

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3659550/

    Mice, on the other hand, do not get Alzheimer’s disease no matter how much you alter their brains to produce amyloid and neurofibrillary tangles. What most mice models of an Alzheimer’s-like disease lack is excitotoxicity. And this is where this study comes in–the same pathways that lead to neuronal plasticity and neuronal regeneration in healthy human brains lead to excitotoxicity in human brains subjected to oxidative stress over decades. What made us more intelligent also made all of us candidates for Alzheimer’s disease.



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  • The study finds evidence that 50,000 to 200,000 years ago, natural selection drove changes in six genes involved in brain development. This may have helped to increase the connectivity of neurons, making modern humans smarter as they evolved from their hominin ancestors. But that new intellectual capacity was not without cost: the same genes are implicated in Alzheimer’s disease.

    Only around 4% of Alzheimer’s cases are diagnosed in the age range of 30 to 61 and many such “early onset” cases advance slowly within the early stage. Obviously AD is a chronic dementia disease of old age, predominantly affecting people in their 70s, 80s an 90s. I speculate that the disease imposed minimal costs on human societies for most of history because relatively small cohorts lived into their 70s and beyond. The “cost” the researcher cites are recent – driven by two related variables which played little role in human history before major strides in modern medicine came on line in the first half of the 20th century. The exorbitant and growing costs of Alzheimer’s Disease are driven currently by two major related factors: (1) Increasing actuarial cohorts living 65+ years and 85+ years; and (2) increasing life expectancy with a growing share of populations living into their 80s and 90s. The prevalence (absolute number) of cases will increase as these two factors increase. Tremendous savings can be made by focusing more on delaying onset and slowing the progression of the disease into the advanced stage rather than finding a “miracle” cure.



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