Evolution Is Killing Our Brain (Slowly)

Youthful advantages lead to the changes behind vascular dementia as we age.

Posted Oct 09, 2019

A hundred thousand years ago, humans died from wounds, bleeding, infections, and starvation. For thousands of generations, we have selected out for people who heal well, clot well, and store calories well. 

That's terrific—but you know what? Evolution doesn't care about us after we are done having children. All of these traits which have kept our species alive eventually work to our disadvantage as we age. The healing process itself will eventually change our circulation, and can jeopardize adequate blood flow to the brain. 

Vascular dementia is the loss of higher brain function due to inadequate or interrupted circulation to the brain. It can be thought of as the consequence of having strokes—big ones or small ones. Vascular dementia, sometimes called senile dementia or multi-infarct dementia (that is, dementia due to many small strokes), to some degree can be prevented, because you can prevent a stroke.

We have vascular dementia because we have strokes. We have strokes because our circulation changes with age. Our circulation changes with age because we have genetically selected for it! In many respects, there is (almost) no such thing as heart and vascular disease: it's just natural aging.

First: we have evolved to heal well. This, of course, makes sense, and allows us to reach adulthood and pass on our genes. But, life itself is traumatic. We have 100,000 heartbeats a day. That's a lot of wear and tear on the inside. The lining of our blood vessels (arteries) have micro-tears every day, and they heal. On the outside, when we heal we see scabs and scars. On the inside, we develop plaque, called atherosclerosis. It is the result of chronic inflammation, or healing.

Atherosclerosis, or plaque in the arteries, is not really a disease. It is a natural healing process and a natural part of aging. We only call it a disease when it manifests as an obvious problem (like blocking blood flow), but over time, even small amounts of plaque build-up in the arteries that lead to our brain will present a problem. The rough surface created by plaque serves as a place where small blood clots form. Clotting is also part of the healing process. When small blood clots form in the arteries of the brain, or when they travel to the brain (and get stuck in an artery), that part of the brain will be deprived of normal blood flow.

Depriving the brain of normal blood flow kills brain cells. Permanent brain damage is called a stroke. The chronic progression of many small brain injuries is vascular dementia.

Evolution has selected out for the fittest to survive. The fittest heal injuries well, but that potential for healing makes vascular healing and thus plaque formation all the more inevitable. We also form blood clots well. Those who clot the best win. But, clots in our brain lead to strokes and vascular dementia.

And let's not forget surviving famine. Those who store calories best also win (in the short term). In the 21st century, calories are in abundance, and we often eat things that we are not genetically prepared to metabolize. That means we store the calories, which leads to disordered metabolism. That is: higher blood sugar, higher cholesterol, insulin resistance, pre-diabetes, and diabetes. We care about metabolic issues because they accelerate vascular inflammation and vascular aging. When we accelerate vascular aging, we accelerate plaque growth and clotting potential, and thus we increase the likelihood of strokes and brain injury.

Have heart. These processes are no longer mysterious. Stroke rates may be rising, but in part, that is because we are not dying of other things (like heart attacks or infections). Aging is inevitable. No one is immune (yes, even Olympic athletes age), but the inevitability makes the aging process predictable, measurable, and manageable.

We can know our health on the inside. Vascular changes do not produce symptoms at first. It is a silent killer, but it is not invisible—vascular aging can be seen and measured. Once you know your health on the inside, you can be armed with the data to give you choices on how to prevent a stroke and brain injury. There is always a personal effort, but sometimes pills and procedures can be helpful too.

Evolution may have driven us to the potential to brain injury, but it also has given us the understanding and opportunity to prevent it.