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Humans are vulnerable to heart attacks and strokes. Our modern diet leads to atherosclerosis, this already starts at a young age but it doesn't cause symptoms until an important artery is almost completely blocked or if a piece of plaque ruptures and causes a sudden shutdown of the blood supply to parts of the heart or brain.

However, if people eat like many indigenous people such as the Tsimané do, then they get far less atherosclerosis:

“Most of the Tsimané are able to live their entire life without developing any coronary atherosclerosis. This has never been seen in any prior research. While difficult to achieve in the industrialized world, we can adopt some aspects of their lifestyle to potentially forestall a condition we thought would eventually effect almost all of us.”

Similar results had been found previously, but this then relates to coronary heart disease not merely the presence of atherosclerosis, see e.g. here:

Williams and Jack Davies had shown clinically and pathologically that coronary heart disease was almost non-existent among the African population in Uganda, although Hugh Trowell had reported a single case of coronary heart disease in an African judge. In the Asian community of Uganda, on the other hand, coronary heart disease was extremely common, accounting for almost half of the male deaths in Kampala in 1956–1958.

The question is then how we could have evolved to be almost free of atherosclerosis when sticking to such a lifestyle, given that atherosclerosis doesn't cause symptoms until it has progressed quite a lot, which is typically late in life and that then in the developed world. For indigenous people like the Tsimané it's even less relevant, because they have a much lower life expectancy due to infections.

Nevertheless it does look like our ancestors did evolve such that they didn't get atherosclerosis.

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    $\begingroup$ I don't think early man lived long enough to get atherosclerosis, even assuming his diet predisposed him towards this, which I doubt. We get it after reproductive age if our diet disposes us to it. I don't understand what you are on about. $\endgroup$ – David Jun 17 '18 at 22:32
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    $\begingroup$ I really don't understand you. Are you saying that the diet of native peoples (= prehistoric man) "evolved" to prevent atherosclerosis and you can't understand how selective pressures produced this? Because that's like saying that prehistoric man evolved to have an alcohol-free diet so that he didn't suffer from cirrhosis of the liver. You could argue that prehistoric man evolved to survive on the diet available to him (hence post-weaning lactose tolerance), but that has no relevance how a modern diet affects health. $\endgroup$ – David Jun 18 '18 at 12:51
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    $\begingroup$ Please read The Blind Watchmaker by Richard Dawkins, it will give you the basic understanding how evolution works. That a certain diet protects against certain diseases does not have to do anything with evolution - it can be (and most probably is) just a random fact. It is possible that tomorrow we invent a completely new diet which by accident will make us highly resistant against let's say the encephalitis - and it will not be the result of evolution. $\endgroup$ – Honza Zidek Jun 18 '18 at 18:10
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    $\begingroup$ I am not interested in a discussion of the effect of diet on health, nor is that the purpose of comments on SE. I used the comment feature for what it explicitly says it is for, to try to get you to clarify your question. You did not respond directly to my enquiry, so I have voted to close your question as unclear. $\endgroup$ – David Jun 18 '18 at 22:38
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    $\begingroup$ @CountIblis Just accept that if a diet has good influence on some potential disease, it is not necessarily related to evolution. Your premise is wrong. So your question "How does evolution eliminate problems..." is a nonsense from the beginning. The answer is simple: the evolution has (most probably) nothing to do with your topic. $\endgroup$ – Honza Zidek Jun 18 '18 at 23:17
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Heart attacks and strokes, and any other diseases that afflict humans after age 35 or so have absolutely no influence on natural selection because for the vast majority of our history, these diseases affect only post-reproductives. Evolution is not a state of advancement toward an ideal, but rather, a mechanism to put genes into the next generation. These genes lag behind our current situation by thousands of years because evolution acts slowly. So evolution still favors characteristics that would have been good for our Stone Age ancestors, who did not live long enough to be weeded out by diseases of old age.

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  • $\begingroup$ Many of our stone age ancestors didn't survive long enough to reproduce. Those who did could live longer than more recent civilizations. $\endgroup$ – anongoodnurse Jun 18 '18 at 3:23
  • $\begingroup$ Heart disease, heart attacks and strokes do not only affect "post-reproductives". They have been known to affect young people too. $\endgroup$ – Chris Rogers Jun 18 '18 at 5:40
  • $\begingroup$ Yes, I agree. "Known to" is correct. How many heart attacks do you think happen before age 35? These are due to other problems. Evolution does not act on the elderly. $\endgroup$ – Karl Kjer Jun 18 '18 at 6:27
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    $\begingroup$ Our ancestors did not evolve to not have atherosclerosis. The study you cited in the Lancet stated that it was the diet and lifestyle that protected the Tsimané from hardening of the arteries. Not adaptation, selection or evolution. $\endgroup$ – Karl Kjer Jun 18 '18 at 12:54
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    $\begingroup$ I have to disagree slightly about diseases after 35 or so not affecting selection. There's what we might call social selection. (Don't know if that's the proper term.) That is, someone of reproductive age who has healthy older relatives to share the burden of child-raising is more likely to have surviving offspring. $\endgroup$ – jamesqf Jun 18 '18 at 18:23
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The question is then how we could have evolved to be free of atherosclerosis when sticking to such a lifestyle.

If this is really is your question, here is the answer. The answer is not biological, it can be answered just by anyone educated in the basic logic.

  1. It is not necessarily true that "we have evolved to be free of atherosclerosis when sticking to such a lifestyle".

The only fact which might be true (supposed the data are correctly interpreted) is that when sticking to such a lifestyle (and maybe also doing something else? or maybe having some enzymes which other population does not have?), these people are free of atherosclerosis. (There are still a lot of questions, e.g. taking into account that they do not live long and atherosclerosis usually does not occur in young age.)

  1. Hence the question is based on an unproven assumption.

  2. Hence the question does not make sense from the beginning.

The question should have been like this:

Is it caused by evolution, that sticking to a certain diet makes an animal free of a disease? How is it in the case of this specific disease and this specific diet?

Such a question would really be a valid question. However yours already assumes something which is not a proved fact and manipulates the answer.

It just sounds to me as one of the weird "arguments" of vegetarians that "humans are vegetarians by nature".

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  • $\begingroup$ Ok. And I agree with your new answer, although I have no idea whether you are right about the poster's agenda. $\endgroup$ – David Jun 20 '18 at 8:04
  • $\begingroup$ 1: Straw man, not literally 100% free but I gave the link where the details are given, and these details are non-trivial as also pointed out in the Lancet article. 2 Follows from 1, therefore based on your Straw Man argument therefore False and 3 does not even follow from 2 and/or 1, so it is totally wrong. Sounds like the argument that "humans are vegetarians by nature"? That's another rhetorical trick to smuggle in a Straw Man argument. $\endgroup$ – Count Iblis Jun 20 '18 at 12:32
  • $\begingroup$ @CountIblis See my edit, straw man! $\endgroup$ – Honza Zidek Jun 21 '18 at 7:00
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How does evolution eliminate problems that only cause diseases late in life?

This is a fantastic question, which still is the subject of intense research. One possibility might be that we age because there is no or little evolutionary selection against diseases late in life (as old people are less likely to produce offspring). As for any active area of research there are several subtleties. You might enjoy starting with the corresponding section on wikipedia: https://en.wikipedia.org/wiki/Evolution_of_ageing#Mutation_accumulation

If people eat like many indigenous people such as the Tsimané do, then they get far less atherosclerosis

This refers to another current research domain, which has only been published in the (really good) medical journal Lancet, where the authors themselves state that several questions remain open, see Kaplan et al. 2017.

Yet their paper already reaches to an important conclusion. While one could hypothesize that the difference in atherosclerosis was due to some genetically inherited property, the authors find support for (and hence favor) the alternative hypothesis, that those people generally live a very healthy lifestyle (e.g. normal BMI, no smoking, ...) which reduces the chance of some diseases.

Similar results had been found previously, but this then relates to coronary heart disease not merely the presence of atherosclerosis

Though it would be tempting that this observation could come from a healthy lifestyle, there could also be several alternate explanations (for instance one could hypothesize their genome contains something that only is under selective pressure within the region where they live, and that this something just happens to also help against coronary heart disease).

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Important to note that a social species like ours has other sophisticated ways to ensure that its genes survive in the next generation alongside the obvious way of "passing down".

Even after our reproductive phase we can teach our children or even take care of their children, which highly rises their chance to thrive and reproduce.

It is also possible to ensure that some of your genes are safely passed, by helping your brothers and sisters to raise their children while sacrificing your direct reproduction, since you have similar genomes.

So even genes carried by infertile people can greatly affect how their identical or very similar instances in their blood relatives will pass through via advantageous social interactions.

Other:

That the Tsimané people have a low life expectancy now does not imply that it was always true. Maybe those infectious diseases were carried in by Western European explorers and conquerors.

You can research the grandmother hypothesis.

Here is a good paper to start.

Update:

The fact that the average life expectancy was low in the past, doesn't mean that nobody lived long. The infant mortality was very high, so relying solely on a average is not wise. Here is good publication on the subject. Mind the first table which shows the life expectancy of the ancient and medieval elite was close to the common life expectancy of the UK in the mid-20 century.

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The discussions about my questions has led me to the answer. Clearly there has had to be a natural selection in our past that leads to a healthy cardiovascular system, otherwise it would be a massive coincidence that the typical indigenous lifestyles involving a mainly plant-based diet supplemented by only small amounts of meat or fish, just happens to lead to extremely low levels of atherosclerosis. But this does not mean that this evolution has had to have happened in our recent past.

The cardiovascular system appeared 600 million years ago:

Existing evidence suggests that the blood vascular system first appeared in an ancestor of the triploblasts over 600 million years ago, as a means to overcome the time-distance constraints of diffusion. The endothelium evolved in an ancestral vertebrate some 540-510 million years ago to optimize flow dynamics and barrier function, and/or to localize immune and coagulation functions. Finally, we emphasize that endothelial heterogeneity evolved as a core feature of the endothelium from the outset, reflecting its role in meeting the diverse needs of body tissues.

Atherosclerosis was then suppressed as a result of natural selection hundreds of millions of years ago when the biochemistry of the heart and blood vessels was fine tuned. So, animals typically don't get atherosclerosis and that's then also true for humans who stick to a natural mostly plant-based diet. But because we've only started to eat a lot more meat and fat in our very recent history, we have not evolved to adapt to our modern diet. The fact that heart disease typically affects us after we reproduce, makes this adaptation very slow.

Polar bears, in contrast, have had enough time to evolve to adapt to their diet. As pointed out here:

It turns out the beasts have evolved genes that allow them to survive on a diet of mostly seals and the blubber those animals contain, not to mention their sky-high cholesterol levels, without developing heart disease.

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    $\begingroup$ It just sounds to me as one of the weird "arguments" of vegetarians that "humans are vegetarians by nature". And it rather looks like you had the "question" ready with this "answer" in advance and you just wanted to make the impression that this "answer" is a "conclusion of discussion". $\endgroup$ – Honza Zidek Jun 20 '18 at 7:36
  • $\begingroup$ @Honza Zidek Vegerarians don't eat meat, not even occasionally. It could be that you are ideologically invested in the Paleo-movement, that you are a fanatical Atkins dieter, but me making such suggestions would be besides the point. You have sidestepped the issue that atherosclerosis that was thought to be natural part of the aging process that no diet or known medicine could prevent, happens at a much slower rate when people stick to a diet that most plant-based indigenous people stick to. They are not 100% vegans, but they get the vast majority of their protein from plants. $\endgroup$ – Count Iblis Jun 20 '18 at 12:13
  • $\begingroup$ @HonzaZidek You just dismiss that fact as probably due to coincidence, your argument being that for a random disease it would not be all that unusual for there to exist a diet that would help with that particular disease. That's good rhetoric, but that reasoning doesn't apply to this case, because the disease was not all that random, it's the nr. 1 or 2 killer, and the diet happens to be a natural diet that our ancestors who lived in tropical areas would typically eat. Perhaps people in ice age Europe had to do with a meat-based diet, leading to a some degree of adaptation to such a diet? $\endgroup$ – Count Iblis Jun 20 '18 at 12:18

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