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Today, I want to start off with a question:  Can a species direct its own evolution?

Normally, when we explore the forces that  shape the evolution of species here on Eons,   we’re talking about external factors… Things like changes in climate  and resource availability or   pressures from competitors and predators.

These common environmental challenges  influence how natural selection shapes all   living things to fit their ecological  niches, from E.coli to elephants.

But what if a species actively modifies  the way it interacts with its environment,   constructing its own niche and altering  the selective pressures it faces?

Well, then it would be shaping its own  evolutionary journey, at least in part.

And there’s one species that seems to have a  habit of doing this over and over again: us.

Thanks to our ability to develop and  share complex learned behaviors across   generations - a thing we sometimes call culture  - we have become the ultimate niche builders.

Cultural changes deep in human history  introduced new selective pressures that   we wouldn't have otherwise faced, by exposing  us to novel situations of our own creation.

These affected our genes, our bodies,   and our evolutionary journeys just like  ancient shifts in climate and ecology did.

And it would take studying the DNA of  people living today to tell the stories   of some of these cultural changes –  from the ones that transformed our   diets to the ones that altered our consciousness.

From a genetic perspective, evolution is simply   a change in the gene pool of a  population across generations.

And if that change has been selected for  by natural selection because it increases   survival and reproduction - a.k.a.

fitness -  then it can be considered adaptive evolution.

It’s a change that helped the organism  adapt to its environmental conditions.

Now, we know that ancient cultural shifts altered  the way that we interacted with our environment.

And this exposed us to new  selective pressures created by   culture that drove the adaptive evolution  of specific genetic changes in response.

One classic example of this is the  fact that around one in three people   living today can digest lactose  - the sugar in milk - as adults.

Humans usually lose this ability after  childhood, like most other mammals.

The gene that codes for the enzyme that breaks  down lactose essentially turns off as we grow up,   meaning that, until fairly recently, everyone  was lactose intolerant as an adult by default.

But, in the Holocene Epoch, multiple groups of ancient people began domesticating animals  that they could milk in parts of Europe,  Asia, the Middle East, and Africa.

And, as a result of that cultural shift towards   dairying, those populations independently  evolved to keep that gene turned on into   adulthood – sometimes by entirely different  mutations that achieved the same end result.

These mutations were selected for  by natural selection because being   able to digest milk as an adult was a  survival advantage for people back then.

And this new lactose tolerance, in turn,  might have reinforced the culture of   dairying and lactose consumption in  a kind of self-perpetuating cycle.

Now, this topic is actually even more complex  and probably deserves a whole episode to itself.

But it’s often considered a textbook case of  gene-culture co-evolution - the process by which   culture can change DNA, and vice versa.

And the deeper we’ve dug into our  DNA over the last two decades,   the more examples of it we’ve found.

On our first chromosome, for example,   is a genetic feature that stands out  compared to our closest primate relatives.

It’s a gene called AMY1, and while other  primates have just a couple copies of it,   us Homo sapiens usually have  many more - about 7 on average.

And we even have more copies than  our closest extinct cousins - the   Neanderthals and Denisovans - who have just  the two copies of our shared common ancestor.

So what drove the expansion of this gene   in us Homo sapiens after our  lineage diverged from theirs?

Well, the gene codes for a protein called  salivary amylase, which is an enzyme that   we produce in our spit that helps us  break down starch into simple sugars.

And having more copies of the AMY1  gene means more salivary amylase,   which means more efficient digestion of starch.

So some researchers think that the  duplication of this gene is the result   of ancient cultural shifts that changed our  diet, much like dairying did with lactose.

This time though, the shift was  towards eating more starchy foods.

Now, this may have happened as far back  as the middle of the Pleistocene Epoch,   as ancient humans mastered and shared the  art of processing and cooking starchy  foods in the wild, like tubers and roots.

Later, the development of agriculture  in the Holocene was another cultural   shift that suddenly increased the  amount of starch in our diets.

One study even found that people from populations  with traditionally high starch diets have,   on average, more AMY1 copies than people  from populations with low starch diets.

Now, diet is a pretty common driver of  evolution, because feeding yourself is   a very important and constantly shifting  challenge that all living things face.

So it’s no surprise that consuming more  starch and more lactose thousands of   years ago left genetic legacies  that can still be felt today.

But gene-culture co-evolution isn't only tied  to exploiting new resources and opportunities.

In theory, a cultural shift that  introduces a new danger can also   lead to the emergence and spread of genetic  adaptations for coping with that danger.

And the form that culture-induced dangers  take can sometimes be pretty surreal.

See, one recurring quirk of human  cultures is their search for emotional,   spiritual, and religious experiences.

For tens of thousands of years, in many cultures  around the world, people have practiced shamanic   rituals to trigger those experiences  - and many communities still do today.

And it’s not uncommon for these kinds  of rituals to feature the consumption   of different hallucinogenic plants and fungi  with traditional significance to each community.

In the Americas, for example, Indigenous people  ranging from the Southern U.S. to northern Chile   and Argentina have used hallucinogenic cacti  in shamanic rituals for nearly 10,000 years.

These cacti naturally produce psychoactive  alkaloid compounds that alter consciousness.

But consuming these alkaloids  can have toxic effects in some   humans - especially pregnant people and children.

In August of 2022, a team of researchers from   Argentina published a study looking at  whether exposure to this toxicity had,   over thousands of years, left any adaptive  genetic footprint in people living today.

They focused on Native populations  from the Central Andes that have a   long history of consuming hallucinogenic cacti.

But first, to figure out what potential  genetic adaptations to look for in their DNA,   the researchers turned to the DNA of a certain  species of fruit fly that  also exploits these cacti.

They figured that if they could experimentally   analyze how the flies genetically resist  the toxic alkaloids found in the cacti,   then they could look for signs of selection  on the corresponding genes in people.

After all, fruit flies and humans have  a surprisingly high proportion of genes   and genetic pathways in common  - it’s part of what makes them   such useful model organisms for the  study of human genetics and disease.

So the researchers raised the flies on both  hallucinogenic and non-hallucinogenic cacti   species and altered the alkaloid  dosage and measured and compared   gene expression under the different conditions.

From that gene expression data,  they were able to find a list of   candidate genes that seemed to be involved  in dealing with the toxicity of alkaloids.

Some of those genes had a corresponding  version in humans, and of those,   ten showed signs of positive selection  in the DNA of Native Andean populations.

And most of these were exactly the kind  of genes that you’d expect to be under   selection pressure after thousands of years  of exposure to hallucinogenic alkaloids.

They were associated with metabolizing,  detoxifying, and clearing chemical substances,   as well as protecting and maintaining the  activity of the brain and the nervous system.

So while more studies are definitely  needed, this may be a rare example of   a religious practice with ancient roots subtly  influencing the evolution of the human genome.

Shamanism didn't just alter the consciousness  of ancient people and their modern descendants,   it might have literally changed their DNA, too.

All of these examples, and the many more  we’ll no doubt find in the years to come,   are a result of the same  general evolutionary principle.

From a gene’s perspective, selective  pressures that come from culture are   no different than the ones that come  from geology, ecology, or climate.

And our fondness for inventing and transmitting  complex learned behavior means that,   more than any other species in the history of life, our evolution has been shaped not only   by the environments we found ourselves in, but  also the environments we created for ourselves.

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So besides dairy and starchy foods - some  humans have another odd dietary preference.

Check out, “How Chilis Got Spicy (and  Why We Love the Burn)” to learn more.

And thanks to this month’s  transformative Eontologists!

Gale Brown, Juan M., Jacksy  Weiss, Melanie Lam Carnevale,   Annie & Eric Higgins, John Davison Ng,  Colton, Chase Archambault, and Jake Hart.

By becoming an Eonite at patreon.com/eons, you  can get fun perks like submitting a joke for us to read.

Here’s one from Matt Hepler.

What is a geobacter's favorite  thing  about a spa day?

The mud bath!

And as always thanks for joining  me in the Adam Lowe studio.

Subscribe at youtube.com/eons  for more prehistoric stories.

I did not know "dairying" was  a word until this episode.

What a word, dairying.