Human generation time:
I have pointed out so often that it bores me (I hope I do not bore you) that civilizations by and large face a three hundred year brick wall. As they approach that time they become evermore vulnerable to eclipse, presumably from infertility among a critical segment of the population. Indeed in the only well studied case, even a little valley that is big enough to feed a thousand faces the same doom at the same time.
I generally say that this is ten generations. It is now time to come clean. Where did I come up with the number? Well I got it from a very unrespectable source: family history. That’s not to say my family isn’t respectable, but we hardly represent a good statistical sample of humanity. But we aren’t really so very bad. And not all of the stories are documented but I think I can get around that.
The first Herbert in America was one Bridget Herbert in the sixteen hundreds. Everyone is well documented since then. Then there is a sort of a myth that we descended from a British Herbert family. They in turn are well documented back to the Norman Conquest. But there is another myth that they were descended from counts of Vermandois. From there those folks are well documented back to Charles Martel and before going back to Mary Magdalene. So the two myths cast a cloud over the ancestry that might or might not be lifted by the right Y chromosome study. But no matter. The myths are still consistent with the time. In other words, the unknown links mean that the people may be in error but that dates are not that bad. If they were bad, the myths could not have arisen. So I went back to Mary and counted generations and divided that into the time and came up with a thirty year generation time.
A lot of those generations involved first sons. That could mean an underestimate or an overestimate so I decided to assume that the effects canceled and went with the thirty years.
For a long time I sort of felt out of touch with everybody else. Most people seemed to assume that throughout most of history life was short. And – if I follow their logic – teenage pregnancy is bad and we are better than our ancestors so they must have had more teenage pregnancy so generations times were shorter. I kind of think people under conditions of cold, hunger, anxiety and no artificial light (I’m thinking that there were great things in olden days but maybe not that great all the time) people matured more slowly. Sometimes somebody will notice that a lot of ancient skeletons are teenagers and be puzzled because in our culture teenagers are the least likely to die. I wonder whether they are really teenagers or older people who were maturing slowly.
Anyway, I now feel more like I am mainstream. An article (An Antipodean Raj ECONOMIST vol. 406 no. 8819 January 19 2013 page 77) that considers the possibility that thousands of years ago people traveled from India to Australia by ship. And the estimate of generation time the article makes is thirty years.
So I’ll take a definite maybe on that one.
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