Moreover, evolution through fixation can occur in the absence of any selective pressure. That is, traits that are neutral with respect to fitness may evolve by chance, particularly in small populations. (A group of 100 individuals who made it to the Americas after a long and grueling trek would fit the bill.) This rather counterintuitive phenomenon is known as genetic drift (Hartl & Clark, 2007; Maynard Smith, 1998).
Fast evolution of traits certainly applies to polygenic traits, such as traits associated with nutrient metabolism. Polygenic traits are traits that are influenced by multiple genes, with those genes acting together to influence the expression of the trait.
Moreover, a mutation in one single pleiotropic gene (a gene that influences various traits) can lead to dramatic changes in interconnected phenotypic traits. This includes traits associated with complex processes involving multiple body tissues, such as glucose and fat metabolism.
Some disagree, arguing that complex traits need much longer to evolve. I wish I could be convinced of that; it would make our understanding of health issues and related predictions a lot easier. For example, we could zero in on Homo erectus as our target for an ideal Paleolithic diet.
Unfortunately, when you look around, you see people with food allergies, metabolic disorders, and other food- and lifestyle-related complications; and those problems cluster among people who seem to share recent common ancestors. Interestingly, in many cases those people do not look alike, in spite of sharing common ancestors.
For example, here in South Texas, it is clear that people from Amerindian ancestry (like me, although mine is from South America) are a lot more predisposed to diabetes than others. There are exceptions, of course; we are talking about probabilities here. Especially common here in South Texas are people with South and Central American Indian ancestry; less common but also represented are descendants of North American Indian tribes such as the Kickapoos.
Very recent food inventions, such as refined carbohydrates, refined sugars, omega-6-rich vegetable oils, and hydrogenated fats are too new to have influenced the genetic makeup of anybody living today. So, chances are, they are bad for the vast majority of us. Sure, a small percentage of the population may not develop any hint of diseases of civilization after consuming them for years, but chances are they are not going to be as healthy as they could be.
Other not so recent food inventions, such as olive oil, certain types of bread, certain types of dairy etc. may be better, in terms of overall health effects, for some people than for others. In fact, they may be particularly health-promoting for certain groups of individuals. The reason may be found in inherited metabolic traits. Learning about your ancestors could be helpful in this respect. The problem is that many people's ancestry is quite mixed; again, I give myself as an example - South American Indian, German, Italian, Portuguese ... and who knows what else.
Another, easier and perhaps more effective, way to figure out what particular foods, and in what quantities, may be healthy for you is to keep in touch with close and distant biological relatives; e.g., grandparents, parents, siblings, cousins (family gathering photo below from: www.lega.co.uk). It is likely that you share genes with them. If several of them developed a particular disease, and they consumed a lot of a certain type of food prior to that, then maybe that food should not be part of your diet.
This may also help you avoid making serious mistakes regarding health issues by acting too fast in response to laboratory test results. Relatives may share some quirky metabolic responses, which could be indicative of a disease at first glance and actually have no negative long term effects, and perhaps some positive ones.
For example, let us assume that a person, let us call her Mary, is in her early 50s and has been consuming a diet rich in refined carbohydrates and sugars for her entire life. Her fasting blood glucose looks pretty good at around 82 mg/dL.
Mary then adopts a diet that includes only vegetables and animal fat and protein. This new diet induces mild ketosis. She then notices that her fasting blood sugar is now 113 mg/dL, much higher than the previous 82 mg/dL. Mary’s doctor tells her that she may be pre-diabetic.
Mary knows that the change in diet was associated with the increase in fasting blood sugar, and reverts back to her diet rich in refined carbohydrates and sugars. Her fasting blood sugar goes down to 82 mg/dL, and she is happy. Her doctor congratulates her. However, she becomes obese and develops the metabolic syndrome in her late 50s, and several related diseases soon after.
Let us now look at a different scenario. After getting the 113 mg/dL fasting blood sugar reading on a mildly ketogenic diet, Mary talks to as many of her living relatives as she can. She asks many questions and finds out that a few of them were big meat and veggie eaters and had the same metabolic response. They are in their 60s and 70s and have no hint of diabetes. In fact, they are relatively lean and fairly healthy. She then sticks to her diet of only vegetables and animal fat and protein for life, and never develops the metabolic syndrome.
This fictitious case is based on the idea that low carbohydrate diets that induce mild ketosis may also induce physiological (not pathological) insulin resistance, leading to a version of the much talked about dawn phenomenon. This phenomenon, in this context, seems to be related to our good friend, but much maligned, palmitic acid. Several bloggers discussed it in excellent posts. Peter at Hyperlipid blogged about it here and here; Stephan at Whole Health Source blogged about it here.
Now, going back to keeping in touch with close and distant relatives. It is important to check your relatives’ lifestyle patterns as well, because diet is not everything, even though it is a major contributor to health outcomes. By lifestyle patterns I mean things like level and type of physical activity, sunlight exposure (which strongly influences vitamin D levels), and frequency and quality of social interactions (which reduce stress).
Regarding social interactions, it is worth noting that humans are highly social beings, and social isolation is almost universally detrimental to both mental and physical health.
References:
Hartl, D.L., & Clark, A.G. (2007). Principles of population genetics. Sunderland, MA: Sinauer Associates.
Maynard Smith, J. (1998). Evolutionary genetics. New York, NY: Oxford University Press.
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