diet & genes: take two

August 12, 2009

In June I wrote about the impact of evolution and migration patterns on diet.  The post came after I attended an event at the Science Museum called “Moving Genes,” and it featured Dr. Mark Thomas, professor of Evolutionary Genetics at University College London.

Whenever I write about someone, I like to send them a link to the post; and I was delighted when Dr. Thomas replied right away.  He attached a couple of relevant scientific papers, which admittedly gave me a minor headache as it has been quite a while since university.  He also very kindly let me know that I had misquoted him!

Now, I actually love it when I’m wrong; because it means I’ll learn something, and in this case it also meant I’d have another post for you.  We agreed to talk the following week to clear things up.

I wish I had hours and hours to speak with Dr. Thomas; his subject matter is so interesting to me it almost makes me want to go back to school.  I’ll try to sum up our conversation:

The human species

In comparison to other species, our biological difference are mostly skin deep.  The operative word here is “mostly”, which I had left out of my previous post.

We all share a common ancestor that lived around 2,500 years ago.  It’s possible that some or many of us do not carry any genes that were inherited from this common ancestor.

If we go back 4,000 years, everybody that was alive was either a common ancestor of everybody alive today or not an ancestor of anybody alive today.  I had to read that one several times, and I’m still not sure what it means.  Dr. Thomas clarified that it’s these points that many geneticists found hard to understand – not the general information I had related earlier.

Milk tolerance

As I learned during out call, just one word can throw off an entire scientific conclusion.  Dr. Thomas corrected my previous assertion about the digestibility of milk amongst Europeans: some of them have only been able to digest milk for 7,000-8,000 years.

During times of drought and famine, populations that had access to cow’s milk – and could digest the sugar in milk – could ride out crop failure by drinking this (relatively) uncontaminated fluid.  Therefore, these groups would survive and reproduce whereas others could not.

Frugivorous origins?

As I mentioned before, I’ve been reading Dr. Douglas Graham’s 80 10 10 Diet – an intriguing read that makes a good case for how humans are designed to obtain the majority of our calories from fruit.  Dr. Thomas said that the best evidence for a frugivorous past is the color receptors in our eyes.  The majority of mammals have two receptors, whereas we and many of our primate cousins have three – the better to identify fruit with.

Meat heads

Again, a clarification:  Populations who ate meat must have had a major advantage, and we can measure this by looking at their genes.

Dr. Thomas says:  “Our brains could not have evolved to be so big unless we had a high-quality diet with a high meat component.  Big brains are just too energetically expensive to maintain without rich food.”  However, he adds that we would have started out as scavengers, not hunters, until we developed tools 2.5 – 1.5 million years ago.

I was in error when I stated, “our brains would not have evolved had we remained at the hunter-gatherer stage.”  Actually, we’ve all been at this stage our entire history up to 10,000 years ago.

I learned a great deal during our call and was of course curious about Dr. Thomas’ vegetarian origins.  He said he went veggie at two-and-a-half years old when he saw his mother plucking a chicken and made the connection between the bird and his dinner.  He says, quite candidly, that he simply finds the idea of eating poultry and seafood disgusting.

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  1. Jess August 17, 2009 at 22:19


  2. green ink August 13, 2009 at 09:46

    Make knowledge your weapon. I like it! :)

  3. Jess August 13, 2009 at 06:46

    Thanks, Debbie! Interesting indeed. I need to look into this area more. Hope all is well.

  4. dhawhee August 13, 2009 at 00:57

    interesting stuff. a friend of mine, Tim White, a biological anthropologist at berkeley, is best known for his theory that meat eating is what helped to create folds in human brains. vegetarians can’t stand him. :)

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