Current thinking on diet and brain evolution?

[Graeme M]

I went to a talk on nutrition recently which led me to do some research. Of particular interest to me is just what early humans ate, but I've also found a lot of uncertainty around what led to the evolution of the human brain.

There seem to be a variety of arguments, from the claim that meat fuelled brain development (common thinking just a few years ago), to starches helped fuel brain development (http://www.journals.uchicago.edu/doi/full/10.1086/682587 last year by Dr Karen Hardy) to cooking anything at all did it.

Not knowing that much about biology I got to wondering about all this conflicting information. I would have assumed that just eating a particular diet wouldn't trip brain development, surely there need to be selective pressures in the environment that favoured the changes that lead to big brains? Sure the high energy demand would require certain food sources, but that seems more likely to me to be a behavioral change as early man found the diets that worked best.

I read that cooking is considered one of the most likely contributors to obtaining more energy from existing diets and there are arguments for fire use as long ago as 1.5 million years.

I assume our earlier ancestors were largely frugivores like other members of Hominidae, but that changes in brain anatomy and the consequent demand for high energy foods might have led to various dietary strategies with no one specific diet being dominant. The result would be a variety of strategies and adaptive changes, which seems to be what we see.

The other thing that I rarely see mentioned in relation to "paleo" diets is what nature is doing. In natural settings, I wonder if it is important for people to live past effective reproductive ages. Thus if a diet is good for people in that it meets high energy demands while one is reproductive, but causes all sorts of chronic disease later, nature couldn't care less (eg I've read that Inuit do alright on a mostly meat diet, but have shorter lifespans on average). That's still a good evolutionary strategy. Today though we might prefer a diet that facilitates living to old age in good health.

Can anyone offer any thoughts about the current state of evolutionary biology in the context of both brain evolution and diet?

 

[jim mcnamara]

You have several statements in your post that you seem to have gotten by reading popular accounts of some scientific work. It is great that you have enough interest to stray into a field that is not your mainstay. But I think there are some assumptions about Science and more specifically about Evolution in there as well.

So let's go from the top.

Natural Selection works on populations by differential survival and reproduction of some individuals based heritable traits. But the process can deal with different traits in different environments. So every single 'model of survival' you mention may have contributed the current genetic makeup of modern humans. So, we keep looking for better models

Here is the crux of the matter: those models are analytic, they tear a multitude observations apart until they reach a point where it is possible to formulate and answer a how question - that is supposed to be clear. We have not developed an accepted set tools to examine Evolutionary history using all of the intraspecies variables (genetics and climate,etc.) that existed for our species, let alone the interspecies interactions that also existed. So these models still have problems. There is no one model that is so wonderful that we can pitch everything else. IMO, E O Wilson's Sociobiological approach is a way to get answers for some of the really hard questions - namely: Natural Selection favors certain really plastic social behaviors in hypersocial species. Ex: ants and humans. So maybe Natural Selection is operating at a level the models you mention do not delve into.

Food gathering is one extremely plastic behavior for humans - you mentioned the Inuit.

In other words most of those models simplify to gain understanding. Therefore, what you mentioned about diet remains operable, but only in the context of:

'gee whiz we removed these layers of complexity and we think we see this one thing'

We cannot really exclude the other layers, necessarily.

Take these papers as attempts, not necessarily "the" answer. E O Wilson included. We still do not fully understand all aspects of human nutrition and nutrition related human behaviors.

FWIW there are also models that employ the known facts about a series wet/dry climate shifts (~50K yrs) in Africa that putatively favored complex behavior and human reasoning - not simply diet. They fostered ever-changing food gathering strategies. And larger brain size.

 

[Graeme M]

Thanks Jim. So in effect, yes my observations that none of the mentioned claims are necessarily THE answer and my suggestion that "the result would be a variety of strategies and adaptive changes, which seems to be what we see" are not necessarily way off.

Having a passing interest in nutrition, but not being in any way an expert on the matter, I am struck by the remarkable diversity of opinion but especially the appeals to some historical heritage. Whether that's animal protein, starches, fish, or whatever. Everyone wants to claim their particular idea as somehow occupying the high ground. Perhaps it doesn't matter that much at all if social strategies and adaptive changes mean that people can get enough energy from whatever they eat (eg Inuit diet, or the change to cooking foods).

I also like the notion that you refer to when you say that other conditions might have "favored complex behavior and human reasoning" that may have led to increases in brain size. That sounds much more likely to my obviously layperson's perspective.

I am still curious about my thought that perhaps whatever diet one pursues in an ancient natural setting might favour selective benefits rather than the modern desire for a long and healthy life in our Western societies. That is, ancient diets may not necessarily mean that a modern person might live a long healthy life should they adopt them.

 

[jim mcnamara]

Hmm.
[opinion]
There are multiple problems with nutrition. First off there are huge business interests involved, secondly humans tend to be incredibly parochial about food choices.

First:Older articles in the field (say 1960's) were often were often funded by what are now viewed as political interest groups - Sugar Institute for example.

In fact, food processors create safe shelf-stable foods. Those foods often come with a downside. The non-caloric nutrient value per unit mass of these processed foods compared with traditional foods made from scratch is not favorable. (In the US) When and if NIH and NAS decide to change the DRI list it becomes a debate. See the references on these things: https://ods.od.nih.gov/Health_Information/Dietary_Reference_Intakes.aspx
These two points about processed foods and RDI are not unrelated, IMO.

Pick one of the DRI reference papers.

So the point here is: Nutrition Science has a tradtion of being a football in the US. We just "celebrated" World Diabetes Day. Type II diabetes is a largely dietary mediated disease. I will leave any correlations up to you.

Second: Humans are parochial about foods. Here is one explanation: http://www.ncbi.nlm.nih.gov/pubmed/7583013 - Amniotic fluid carries taste "samples" to the fetus, in this case, garlic. Following along the same path: http://www.ncbi.nlm.nih.gov/pubmed/26773029

Point: if Mom eats certain foods, baby develops a taste for those foods. This was a very adaptive trait before the advent of Red Baron frozen pizza. Baby ate and liked what Mom ate, and obviously she was eating what was available. Not now. Modern US diets include processed foods.
[/opinion]

With all of that going on, I tend to question a lot of research that claims:
"humans should eat ______"
"humans evolved because they ate _____".

But - as a counterpoint to your model of eating high protein diets to have more kids and then dying early:
http://rspb.royalsocietypublishing.org/content/282/1803/20142808
This is part of the whole 'Grandmother Hypothesis' -
https://en.wikipedia.org/wiki/Grandmother_hypothesis

This says, among other things, that having grandmothers around is very adaptive to the survival of offspring.

So, touche!
I don't know what happened to the grandfathers... maybe they ate too much Red Baron Pizza.

 

[Laroxe]

There are always problems in ideas that talk about things in the environment driving evolution, this is a bit back to front really, things have to be present to be selected and presumably a larger brain would help in securing adequate food. Other primates are often quite happy to scavenge meat and some hunt so its very difficult to make any sort of generalised guess about the early diet of human groups.
It seems that very quickly chose to concentrate in areas that had high protein food sources like coastlines or near rivers and we certainly didn't evolve to live in a particular environment following a particular lifestyle. In terms of the brain the main issue would be its high energy requirements rather than protien rich foods. Our big advantage was in our adaptability and as mentioned our cooperative nature.
While meat is certainly a nutritionally dense food source humans can survive quite well on a plant based diet for this to be a controlling factor in brain development we would have to imagine a state of chronic starvation really and that would still effect brain development.