We often try to understand things by bringing an argument the kind of "if it wasn't good for us, we would had lost it" or "if that's what it is now with us, it must be good, it must be what evolution deemed best for us". I think this argument is sometimes misleading. Indeed evolution always helped finding treats that made the chances of survival higher... right? but survival to what point? There is no evolutionary benefit of living till you are 80 unless you can still procreate. From evolutionary perspective if you managed to have grandchildren, you succeeded, even if you didn't live long enough to see them.
I remember reading a fascinating book "Survival of the Sickest" by dr. Sharon Moalem. I had a chance to meet him informally when he was finishing this book and he is one of the most amazing and passionate people I've met. He is a geneticist, finishing his medical degree and generally awesome person. He was the first from whom I heard about the veggies who don't want to be eaten, the danger of soy and its methods of controlling animal population in it's region, as well as the most interesting of them - how many diseases helped us survive. His point was, that if something helped you survived a bit longer, till you could procreate, it was good from evolutionary perspective - even if it made you die at 35 of diabetes, heart failure, iron poisoning etc.
For example - his theory was that child-onset diabetes helped survive extreme cold temperatures during the small Ice Age (high sugar in blood slows freezing of blood, and prevents creating water crystals that could puncture the cell walls), genetic disorder of extreme high levels of iron supposedly helped survive bubonic plague and so on. I can't remember all, and I lent my book to someone.
So I've been thinking... how much of what we consider "good b/c evolution otherwise would get rid of it" isn't that good at all? And what we have to deal with b/c it is supposed to help us (or our descendants) another ice age (that would be thyroid problems for example)? How much "good" is only in particular consequences and simply is a side effect of our ancestors' temporary (thousands of years obviously) circumstances? We know now, thanks to epigenetics, that DNA can be influenced ("switched on and off") much more powerfully than we thought before, even if we do not understand all the processes involved. I wonder how can we know what was for sure evolutionarily beneficial to the species as a whole (easy one - switching to animal protein and fat helped brain development) and what is a genetic scum left in us as a result of particular circumstances that the whole species or only subgroup (like northern European who had to deal with the small Ice Age) had to deal with for longer period of time?
I know it's more of rambling than a clear question, but I find it fascinating to just ponder the complexity of our nature and evolution, and also the still quite shallow depths of our knowledge about ourselves.
Please let me know if that kind of writing is not allowed, so it can be deleted.
There is no evolutionary benefit of living till you are 80 unless you can still procreate.
Evolution can also act through group selection. It's been speculated that humans beyond reproductive age often still served to benefit their tribe either by being able to either bring in more resources than they consumed or by carrying forward useful knowledge (like "no, don't eat those, they will kill you")
Humans are rather unique compared to other animals in this regard. You can read about this in the anthro/ev bio literature.
Good on a personal level and good on a species level are entirely different ideas.
Maybe it's good for the human species to have a die off of a coupla billion metabolic disorder/diabetic/cancerous/coeliac/cardiovascularly compromised/Alzheimered/diseased-by-civilization folks, (ecological detox? Gaianic Herxheimer Reaction?) leaving the Earth to the descendants of folks who are better able to handle GMO grains, sugars, dairy, and industrial oils.
However, it's not good for me, so I'm not about to sit back and let myself be disabled or eliminated any earlier than necessary.
This is exactly the story of agriculture. Growing grains allowed the species to reproduce to epidemic proportions and for civilization to exist. Is this good? In many ways yes. It still doesn't follow that eating grains is good for an individual.
As others have pointed out, though, just reproducing is not the whole story of evolution, since anything that gives your offspring an advantage will be selective, including having grandparents.
I think agriculture allowed us to live in larger numbers in one place. This gave us an immediate advantage when it came to warfare. We could build forts, stock food, and build mass hoards of weapons and armies. THose that did not go to agriculture could easily be wiped out by an organized larger army. Cultural evolution happened faster than the body could compensate with biological evolution though, and the body pays a price. And also the new system allowed for more people with more specialization, like educators, which may have counterbalanced to some extent the problem of people not living as long. Of course, once those agricultural civilizations become fat and lazy, they were still sometimes victims of roving migrant attackers. But even those attackers lived to a large extent by stealing from the agricultural food sources and civilizations around them as they went along. So they were still dependent on the agricultural society as well.
Your question oversimplifies and glosses over an important distinction - "positive" is a determination that's relative to geography and time.
On a long enough timeline, natural selection will always promote those genetically determined traits that are survival or competitive determinants for a given set of external conditions. Traits that are not genetically determined are not subject to evolution. Traits that are not determinants of survival within a given environment are not subject to evolution. And the external conditions vary widely across geography and time.
Anybody who says "X is good otherwise evolution would have gotten rid of it" is using flawed logic unless X is:
I think that in a lot of our thinking about evolution there lurks what philosophers might call a "hidden premise."
Why is it that we feel the need to defend against the argument that natural selection doesn't care about you after you reproduce? Indeed the "kin selection" response is helpful (that grandmothers and grandfathers were useful, etc.). But in using this response we've already given in to the opponent; we've already decided to play the game according to his terms. Because when someone suggests that eating paleo might only be healthy until the age of common reproduction, he is operating from the assumption that a post-agricultural diet is better. That is, he already assumes that his post-agricultural diet is healthy, and that ours is the risk. In our arguments with conventional eaters, we often share this assumption without realizing it. This is the "hidden premise."
What would be the proper way to think about the debate? Well, we have to keep the two positions on an equal footing. We do it like this. Ask which one is more likely: that the diet we have been eating for only 10,000 years might keep us healthy beyond the point of reproduction, or that the diet we ate for 1,000,000 years (or whatever figure) might keep us healthy beyond the point of reproduction? If both positions begin with the same presumption of neither truth nor falsehood, then there's a fair fight -- and it's pretty obvious who the winner is.
So the next time you are being antagonized by a non-paleo, make sure you don't let him "frame" the conversation with his assumptions. All of our other arguments can be helpful too, of course; that I wouldn't deny. But I think it's also helpful to get the right starting-point.
And, by the way, I was having a little bit of fun with my antagonistic language. All of this can proceed with your conversation partner in a calm, truth-seeking sort of way.
The main concept of the paleo diet is based on the so called mismatch between our EEA (Environment of Evolutionary Adaptation) and our current lifestyle. This is a really strong concept, if you ask me, and has implications that go beyond diet, ranging from physical activity, barefooting, sunlight, social context, artificial lighting, ...
Now this is only one part of looking at health and disease from an evolutionary point. Another point, as you mentioned, is that natural selection cares about gene reproduction, and not necisserily about health. Health is only important if it tributes to greater reproductive succes. The most cited example of this principle here is Sickle Cell Anaemia in people from West Africa (or Afro-Americans). See this wikipedia page
Another part of evolutionary medicine is that natural selection is all about trade-offs, with gene reproduction as major goal. The female pelvis is a trade-off between being wider for easier childbirth, and being smaller for better locomotion. 'Growing' a trait has a cost, and natural selection makes a kind of economic 'decision' and makes the trade-offs.
If you want to know more about these topics, try googling Evolutionary Medicine (or Darwinian medicine), or read the great book Why We Get Sick by Nesse and Williams (although they're wrong about the diet stuff). Or start on these websites:
This is an important question that can be answered from different angles. Generally it makes sense to adopt a diet similar to that of our Paleolithic ancestors. But evolution can happen fast (in a few hundred years), so one's more recent ancestry can also make a difference:
Another issue to bear in mind is that, like most animals, we also evolved costly traits. As a result, our ancestors might have evolved some eating habits that are bad for human survival, and moved away from others that are good for survival. The fundamental reason for this was already mentioned in your question; namely, evolution leads to maximization of reproductive success, no survival success.
Finally, there is the issue of inclusive fitness, which is related to Brandon's answer. It is not exactly group selection, but rather gene-centric selection. In short, we may have evolved traits that maximize the replication potential of certain genes we carry, even at the expense of our lives. See this link:
In short, evolution is very helpful as a guide and general explanatory framework, but we also need to use empirical research and some commonsense.
Shifting to an agricultural diet gave an short-term advantage to those cultures who did so against hunter-gatherer cultures. The same for dairy consumption -- those genes spread because they conferred an advantage.
It's been noted here that this can work against the health of the individual. With enough time, those who make the switch would fully evolve to thrive on an agricultural diet. But do you want to put yourself through this process consciously?
The short-term advantage may get wiped out by the long-term disadvantage of an unsustainable food base, total environmental decimation, and general malaise.
The agricultural system could be propped up by reforms and sustained, or it could be scrapped.
Another example that fits your scheme of evolution favoring the sick is Cochran's explanation of Ashkenazi Jewish propensity for genetic diseases. Not a genetic bottleneck as previously supposed, but a side-effect of rapid evolutionary genetic selection for increased intelligence.
First, it seems clear that there is a evolutionary benefit to outliving reproductive age or women would not have evolved to undergo MENOPAUSE... Grandmother hypothesis anyone?
Second, I'm not sure what you mean with respect to men since men can reproduce even in old age...
Based on points 1 and 2 above, I don't agree that we evolved to die early and, thus, we must trick evolution by eating newfangled factory foods and gulping expensive pharmaceuticals.