How many generations separate you from the inhabitants of the earliest human civilisations? How far back in your ancestry would you need to go to be concurrent with the emergence of civilisation? Take a guess, intuitively, without trying to work it out (resist the temptation please). I'm interested to know how your initial guesses compare to the reality, which we'll work out now with the help of a bit of back-of-envelope calculation and search-engine-fu. Think of it as an experiment.
Wikipedia says that the earliest human civilisation is possibly Sumer in ancient Mesopotamia, though some historians believe the Harappan civilisation of the Indus Valley is slightly older. (Egypt was just a couple of centuries behind.) The earliest civilised artifacts have been dated around 3500 BCE.
The average length of a generation (birth to reproduction) today in the western world is a little under 25 years, but over the course of human history, with everything that that implies, it's certainly much lower than that. I couldn't find any good data to base this value on, so I'm wildly guessing. It's pretty likely that the average length of a generation over the last 5500 years is somewhere between 15 and 20 years. I guess the number 18 will do for our purposes since the result is only going to be a very rough figure anyway. (Tangent: try googling for length of a generation sometime and see just how much fundamentalist Rapture analysis pollutes your results.)
5500 years @ 18 years/generation = 305 generations
Anyone else as surprised as I am by that? My intuitive feeling (though I didn't think of a specific number beforehand) was that it would be much greater. Having said that, I've asked other people before and they didn't seem too surprised by it. Grateful for your thoughts on this one, and particularly interested in your initial guesses -- is it just me?
I struggled to come up with an estimate really. The temptation to say "hmm, 20 years per generation, 6000 years, call it 300" was too great.
Vaguely relatedly, did I read somewhere that there are as many humans alive today as have ever previously been alive but since died? It seems a bit hard to believe that the world's population is growing quite so fast, but, maybe it's levelled off recently, or something, I dunno.
30 seconds on wikipedia later, it seems just 20% of all humans from the last 6000 years are still alive. Which is still a lot, but rather more feasible. http://en.wikipedia.org/wiki/World_population knows all.
I fortuitously guessed 300, I'm afraid, but it was (superficially) a completely arbitrary guess.
Could well just be me then.
I just find it really surprising that you can take the common property of children thinking their parents are old-fashioned and silly, repeat it 300 times, and you've gone from the pharaohs to the sequencing of the human genome.
It's certainly counterintuitive; I suspect that listening to Dawkins continually bang on about just how much can be achieved, genetically, in each generation (a complete eye after only 400,000?!) has eventually taught me to be a bit wary of thinking of a human generation as having insignificant duration, even with respect to those yawning chunks of geological time that evolutionary biologists have to deal with.
And really, we're talking about the entire [reproductively] useful portion of a human lifespan here, which to be honest is about the longest interval whose size I can seriously grasp.
Civilisation is a result of farming, a recent invention. But, humans have been around in other social arrangements (tribes, nomads etc.) for much longer.
So, I'm not surprised by the figure.