The DNA Conundrum

Critics of the Paleo diet state that we have evolved to eat dairy since the advent of agriculture 10,000 odd years ago . This idea is generally proposed in such a way to suggest we developed lactose tolerance in response to centuries of consuming milk products . I am not arguing that people do or do not have genes for lactose tolerance . This proposal is just not how I understand Darwinian evolution . I understand evolution as random mutation and natural selection . We do not pass on genes we are not born with . A random mutation has to have occurred during meiosis and mitosis . Our individual adaptations to the environment within our own lifetime do not pass on to our children . So , I {amateur biologist that I yam} can envision two scenarios . One scenario , millenium before agriculture , a random mutation occurred in the DNA structure of some person and lay dormant but successful in the gene pool . Perhaps a mutation of the gene that allows us to digest our own mothers milk mutated to allow us to imbibe other species milk into adulthood . Later as milk came to be consumed regularly those who carried the gene for lactose tolerance survived and thrived . Those who did not , also survived and managed to breed offspring anyway {thus the lack of genes for lactose tolerance in the modern gene pool of cultures with milk based diets} or died in childhood from diarrhea . Second scenario , same as the first only occurring after the advent of agriculture .

The same argument applies to those that propose we developed genes for digesting large amounts of grain in response to a grain based diet . Some may have those genes , but not as a selected adaptation response passed on to the next generation .

Randomly mutated genes selected in nature by the laws of survival are those that win the day and are then passed on . That's how I see it , anyway !

I'm no expert on this, but as I understand it there have over the past 10 years or so been huge advances in the understanding of epi-genetics that haven't yet made it into mainstream understanding.

Key principals are that not all genes that are present in DNA are expressed.
That environmental factors can trigger the expression of certain genetic traits.
That some of the DNA present outside of the nucleus (RNA) is responsible for expressed traits.
That RNA can be passed on from parent to child much as DNA is.

Short version - it is all a lot more complex than we used to think, and the epigentic mechanisms can most likely explain evolutionary changes that appear to take place over too short a timescale for new genes to form.

I think we all participated in this discussion which also brought us around to epigenetics:

wayne stephen wrote:Critics of the Paleo diet state that we have evolved to eat dairy since the advent of agriculture 10,000 odd years ago .
...
The same argument applies to those that propose we developed genes for digesting large amounts of grain in response to a grain based diet .

I think the issue is not so black and white which probably screws up both sides of this debate. Certainly all humans start out being able to consume dairy! Grain seems to have anti-nutrients so I give grain a thumbs down and dairy a thumbs up.

Toby H explains that when we switched to grain our health suffered dramatically (can't remember the exact location in this vid):

I was referring to statements by scientists such as this one in Scientific American :

"Within a span of 7,000 years, for instance, people adapted to eating dairy by developing lactose tolerance. Usually, the gene encoding an enzyme named lactase—which breaks down lactose sugars in milk—shuts down after infancy; when dairy became prevalent, many people evolved a mutation that kept the gene turned on throughout life."

From this article : http://www.scientificamerican.com/article/why-paleo-diet-half-baked-how-hunter-gatherer-really-eat/

The use of the term dairy here is far to broad. 4 teated ruminants (cows) milk is completely different on a molecular level that 2 teated ruminants milk (goats and sheep). The later is superior in every nutritional way and an exponentially more digestible by homo sapiens. I don't think that's a coincidence, we are a 2 teated species.

wayne stephen wrote:
"Within a span of 7,000 years, for instance, people adapted to eating dairy by developing lactose tolerance. Usually, the gene encoding an enzyme named lactase—which breaks down lactose sugars in milk—shuts down after infancy; when dairy became prevalent, many people evolved a mutation that kept the gene turned on throughout life."

From this article : http://www.scientificamerican.com/article/why-paleo-diet-half-baked-how-hunter-gatherer-really-eat/

It's important to point out that not all people adapted. Specifically, lactose tolerance is highest in Europeans and low in people from other continents. Which explains why those other cuisines have a dearth of cream sauces and cheeses.

Fermented milk products (buttermilk, yogurt) have a little wider spread than straight dairy; perhaps it was one of the steps to people adapting to be able to consume milk past the usual weaning age.

Wayne, I think there are fallacies within fallacies embedded in that article! It's a pretty interesting topic though.

Personally, I stick to what people like Gary Taubes & Peter Attia say which is that low carb diets are healthier & better for weight loss. They start with scientific reasons for their theories rather than adding them on to a premise. I think both are OK with someone eating dairy if their body can handle it. Cream is better than milk because is has less carbs. Both are not OK with grains because they are high carb. Not sure how much play they give the "anti-nutrients" in grains. Taubes is kind of wary of high carb fruits - certainly for weight loss - but also because we've made them so much sweeter than they were 10,000 years ago.

It would not surprise me to learn that babies/young children who were lactose intolerant but fed milk products would be more apt to die before reaching breeding age. Their health and immune system would be compromised leaving them more susceptible to dying from other illnesses. And as children they might be more unthifty in general. Babies who don't grow up and reproduce don't go on the represent the population's genetic makeup, thus lactose intolerant humans would be less common as the generations went on.

wayne stephen wrote:I was referring to statements by scientists such as this one in Scientific American :

"Within a span of 7,000 years, for instance, people adapted to eating dairy by developing lactose tolerance. Usually, the gene encoding an enzyme named lactase—which breaks down lactose sugars in milk—shuts down after infancy; when dairy became prevalent, many people evolved a mutation that kept the gene turned on throughout life."

So is it fair to say you have a beef with the scientists who are dismissive of the paleo diet? I think that's reasonable because they are putting forth a theory as fact (people adapted to eating dairy by developing lactose tolerance). We don't know when or how lactose tolerance happened - only that it did express itself.