Science Sundays: Culture and Biology working together (Lactose Tolerance)

By: Meradeth Houston on 9:19 AM

Welcome back to Science Sundays! I hope you have been enjoying a little random science on the weekends :) Today I thought I'd talk about what can happen with culture and biology get friendly with one another, leading to selection for some kind of trait. Specifically I'm thinking about lactose tolerance, however this kind of thing could work for other traits, given the right kind of environment, and might play well in a fun futuristic story. So, here goes:

Most of the world can't process milk once they have been weaned. The gene that produces lactase, the enzyme that breaks down the sugars in milk, turns itself off once it's no longer needed. So when people who don't have a whole lot of lactase in their system have milk, it usually gives them some serious gastrointestinal issues. No fun. (I can't imagine a life without ice cream. Or cheese. Or hot chocolate...)

Anyhow, there have been a few instances where there have been mutations that keep the gene that produces this necessary enzyme turned on, even after a person's no longer getting their milk from their mother. Handy, right? It's important to remember that this mutation was a totally random event--just because it's handy doesn't make it more likely to happen (for some reason this never sinks in with my students...I think they like thinking that if they really needed some kind of mutation it would just magically happen, thank you X-Men!). So, yeah, the mutation itself may have been totally random, but the places where it's been selected for aren't.

This is where things get nifty: in cultures where pastoralism (ie, herding cows and animals with udders) is prevalent, the mutation to keep this gene on throughout life has been selected for. These peoples find this mutation useful and beneficial, and those with it contribute more copies of this gene to the next generation. Presto--positive selection for this variant of the gene! (AKA, this allele, or gene variant.) I love instances where culture effects biology :)

The other cool thing about lactose tolerance? It's developed independently twice, all on its own. Once in Europe and once in Africa. This is a classic example of convergent evolution--where the same kind of trait has developed to a similar environmental stimulus independent of one another (so, not because they share a common ancestor). Another example would be wings in birds and bats--they developed independently of one another. Cool, right?

My students have a paper due on this topic next week. Hmm, chances of them seeing this entry? Very slim. I hope!

So, can you think of any ways biology also might change our genes? Maybe something interesting you want to use in a story? Do share in the comments!