Also relevant: lactose tolerance is something we start out with, babies need it. So lactose tolerance, or more properly lactase persistence, was not the development of a brand new trait out of nowhere, it was maintaining a capability past the age where it would previously degrade out of functionality.
To frame what we are discussing, I hope we can all agree: mutations are happening all the time and in aggregate we each individually carry a vast quantity of genetic differences/mutations apart from every other individual.
For lactose tolerance, really what we are talking about is more natural selection. At least I think we are. As an example, a population can change very quickly via natural selection if an event kills off everyone that is missing a mutation. That perhaps 1% mutation suddenly becomes the surviving population. (For completeness, I'll mention that this process can happen more slowly as well over time, but it can depend on single mutations, aggregates of mutations, and environment and random luck [eg: asteriod] are all factors). This is to say, there could have been plenty of lactose tolerant people well before. This NPR piece on the history of lactose tolerance states it well [3] "But now that doesn't happen for most people of Northern and Central European descent and in certain African and Middle Eastern populations. This development of lactose tolerance took only about 20,000 years — the evolutionary equivalent of a hot minute — but it would have required extremely strong selective pressure."
With the issue of natural selection out of the way, what I do wonder is how long it took for the brain to get the way it is today. According to this resource, The Smithsonian [1], the answer is approx 7M years, with most of that happening in the last 2M years until 200k years ago. That is in terms of 'size' (does not account for wrinkles).
According to 'newscientist' [2], the shape (now talking wrinkles here) of the human brain today is very similar to what it was 160k years ago, and has not really changed since. The resource mentions that the biggest changes since then have been in how our faces look rather than how our brains are shaped. Those changes are specifically smaller jaws: "Faces in modern humans are far smaller, with subtler indentation, than those of their ancestors. Studies show that this change accelerated when hunter-gatherers became agriculturalists around 12,000 years ago and ate softer foods, probably due to less loading on the skull from chewing."
Summing up, given that brain shape has been about the same for the last 160k years; it's plausible that is how far it goes back for people that felt & thought about exactly the same way we do today. If anyone knows about more research around the rise of human cognition on this topic, I'd certainly like to learn more.
[1] https://humanorigins.si.edu/human-characteristics/brains
[2] https://www.newscientist.com/article/2331652-shape-of-human-...
[3] https://www.npr.org/sections/thesalt/2012/12/27/168144785/an...
The adaptations for social organization seemingly have been with us for a long time. AFAIK humans have been in large groups for a very long time, as long as they have been homo sapiens (Large being over 50 members, and take that with a grain of salt, that is only my possibly incorrect understanding).
I do find it very plausible that people 1k, 10k, 50k and maybe even 200k years ago were all smart (Plato probably is far smarter than most alive today). Though, smart and education are different, while smart- the body of knowledge was limited.