Humans have long needed a way to keep track of numbers as they count. In many cultures, finger counting is common. If you live in the United States or China, you probably count to five like this, but there are many different ways to achieve the same goal. (1/8) Image
Variations of five-finger counting exist all around the globe, and between languages, as well. The Pekai-Alue in Papua New Guinea are notable in that the folded, rather than the extended, fingers are the ones counted. (2/8) Image
What happens when you need to count past five? Well, then it gets more interesting. In the US and much of Eurasia, the counting continues onto the other hand, up to 10. If you need to go past that, you often just repeat the cycle from the beginning. (3/8) Image
But other cultures have made clever use of other body parts for counting, such as toes and knuckles. Others, such as the Oksapmin counting system, work their way around 27 body parts. (4/8) Image
And actually, why limit yourself to just integers? The Romans used their fingers to keep track of numbers up to three decimal points, and old Chinese had a way of tracking up to four. (5/8) Image
These are all body-based representations of numbers, but humans also have lots of other counting aids, like tallies. You may be familiar with this system, which tallies with vertical lines up to four, then strikes across to represent five. (6/8) Image
But other systems for tallying exist, like the one below which sequentially forms the Chinese character 正 (pronounced zhèng, meaning "true" or "correct"), or the one further down that completes a little box with a line through it. (7/8) Image
This is just a sample of how counting systems vary, but should give you a little insight into the fun & clever counting aids that have culturally evolved. For more, check out the Bender & Beller paper below (where most of the figures are from!) (8/8)…

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More from @DorsaAmir

11 Jan
I’ve recently been reading through “The Butchering Art”, a terrific account of 19th century surgery & the introduction of germ theory & anesthesia to Victorian medicine. I highly recommend reading it yourself, but here are some interesting tidbits that caught my attention (1/10)
(2) First, as you can imagine, early surgery was absolutely awful & almost always a last resort. One thing I didn’t realize was that back then, the best surgeons were the *fastest* surgeons — for instance, Robert Liston could remove a leg in less than thirty seconds (!).
(3) Early surgery was limited to “peripheral” conditions, like lacerations & fractures. This is because entering the body in surgery was almost always fatal due to infection. This led to the distinction of physicians practicing “internal medicine”, a term that still persists.
Read 10 tweets
9 Oct 20
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/
Read 6 tweets
15 May 20
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

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