Twenty three thousand is a big number. Or is it? Depends on what one is referring to. Most experts expected more. Maybe lakhs, they thought.
Genes. The three base pair sequences in the massive molecule of our DNA. Every one of our cells has a copy. About 23000 of them determine what we are- as far as it can be determined. It is actually, quite a simple blueprint for something as complex as you. Or me. Everyone. The genes split to a corresponding half and join with the version of the other sex other when a baby is produced. The genes are actively shuffled by a process called crossing over. Nice name.
The thing is that the variations in the shuffling process can be studied and analyzed mathematically. This can help us trace our origins in evolutionary time.
It turns out that our particular version of Homo, Homo Sapiens sapiens, is about 200’000 years old. A small band of people, about 2000 individuals, crossed the small sea bridge from Africa to Eurasia to populate the rest of the globe. That was 70000 years ago.
Most of us; outside Africa, are their descendents.
Gene analysis tells us frequencies of which genes changed in the population and at what time. It turns out that in our entire history, at about 10000 years ago, drastic gene changes are observed. Obviously due to selection pressure. What happened to our ancestors around this time?
From hunting occasional game, fishing, and gathering fibrous fruits, tubers and nuts, we turned to farming grains and cattle.
The genes that changed?
Genes for fairer skin colour, as we adapted to colder areas with less sun. The gene for Lactase, to digest milk, during adulthood.. Majority of Africans are lactose intolerant as adults.
Then comes the surprise. Genes associated with Diabetes and Hypertension. They show changes , from a population genetics viewpoint, from 10000 years ago. That must be because these diseases appeared or became much more common as our diet and habits changed. These genes must be showing protective changes. Despite them, these diseases progressed.
Elaborations of some of these ideas are there in the book- ‘Health and Happiness without Bullshit.’
Broadly. Our hunter gatherer forefathers:
-Ate less, in general. All present day hunter gatherers are thin.
-Ate much less refined carbohydrates and grains.
-Probably had to exert more, physically.
Much more remains to be discussed.
To conclude, history is a science.
We can learn from history, sometimes about the most unexpected things.