Culture can evolve rapidly, much faster than genes. Due to this, cultural changes can create new environments that in turn shape our genes. This is called “culture-gene coevolution” & there are some really cool examples of it in humans, especially when it comes to our diets. 1/
The classic example is “lactase persistence”. Most mammals can break down the sugar in milk — lactose — using an enzyme called lactase. But, in most species, this enzyme goes away around the time they stop nursing. Why is it that a third of adult humans can still digest milk? 2/
The answer is culture. In some "hot spots", people started herding animals. This opened up a new resource: animal milk. In at least 2 events, mutations that let people keep producing lactase were selected for. The variant in the Middle East is likely due to camel milk 🐫 3/
A note here, however, that in addition to genetic solutions like lactase persistence, there are also cultural solutions to the lactose issue! Many cultures turn milk into cheese or yogurt, which lessens the issue by using bacteria to digest some of the lactose for us. 4/
Another cool example is domesticated starchy foods & amylase, an enzyme that breaks down starch. Amylase can be found in our saliva, which starts digesting food before we swallow. Cultures with starch-rich diets have multiple copies of the gene (AMY1) that makes the enzyme. 5/
A last example comes from the Bajau people, who are experts at free-diving to great depths to spear fish. This cultural practice has resulted in unusually large spleens, which store & release oxygen-carrying blood cells, & other genes variants that help support diving. 6/6!

• • •

Missing some Tweet in this thread? You can try to force a refresh

Keep Current with Dorsa Amir

Dorsa Amir Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!


Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @DorsaAmir

15 May
In the ongoing battle against herbivores, some plants have evolved unusually clever defenses 🌿 Here are a few I find particularly interesting. (1/6)
Some plants pretend to be infested by aphids to keep actual aphids away. On the left is a branch of Paspalum paspaloides, with a number of dark anthers on it that look like aphids. Compare that to an actual aphid infestation on the right. A pretty compelling copy, no? (2/6)
In addition to growing spines and thorns to keep predators away, some plants enhance the effect with “automimicry” — copying the patterns of their spines on their leaves to look more ferocious. Below are a couple Agave plants showing off this trait. (3/6)
Read 7 tweets
27 Nov 19
Chess is one of the oldest games in the world — stretching back more than a millennia — and a fascinating example of cultural evolution ♟️ Here are a few snippets from its rich history. (1/7)
(2) Chess likely comes to us from India. The original name — chaturaṅga (चतुरङ्ग) — meant “four (military) divisions”: infantry, cavalry, chariotry, & elephantry 🐘 Indeed, the bishop was originally a war elephant & is still called so in many places. In Mongolia, it is a camel.
(3) From India, chess moved into Iran. Ancient Persians (c. 700-800 AD) introduced the idea of warning the other player when their King was under threat. The term “checkmate” comes from the Farsi term “Shāh Māt” (شاه مات) meaning “The King is helpless”.
Read 7 tweets
17 Oct 19
Ever wonder why humans are the only animals that need braces? 🦷 Turns out this is a relatively recent problem for us. (1/5)
If you look at the fossil record, you’ll find that our ancestors’ teeth look surprisingly good. While there’s some evidence for ancient dentistry using tiny flint tools (ouch), there was very little need for ancient orthodontists. (2/5)…
So what happened?

Well, to put it simply: industrialization. As our diets changed, so did our eating habits. We started to cook softer foods & eat with utensils.

This led to a big change: we stopped chewing as much. (3/5)
Read 9 tweets
26 Mar 19
There's a good chance that a bunch of the scientific ideas you’ve learned are now outdated and debunked. Here are some of the ones I feel most strongly about 👇 (1/7)
Are you an ENTP or an ISTJ? Turns out it doesn’t matter ¯\_(ツ)_/¯ The Myers-Briggs personality questionnaire has pretty poor validity & reliability. It's basically astrology. FYI, the "Big Five" is a way better personality framework. (2/7)… A listing of the different Myers-Briggs personality types.
You may have heard that women who live together start having their periods at the same time. Nope. This phenomenon, known as “menstrual synchrony”, is likely not real. A good review can be found here:… (3/7) A picture of two women together with the caption
Read 7 tweets
15 Jan 19
Did you know the human body is full of evolutionary leftovers that no longer serve a purpose? These are called vestigial structures and they’re fascinating. (1/8)
Put your hand flat on a surface and touch your pinky to your thumb. Do you see a raised band in your wrist? That there’s a vestigial muscle called the palmaris longus. It used to help you move around the trees. About 14% of us don't even have this muscle anymore. (2/8)
Check out your ear. Do you see this little bump? That’s called Darwin’s tubercle. It used to help you move your ears around. Now that we have super-flexible necks, we don’t need these anymore. (3/8)
Read 10 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!