One of the unique features of humanity is the progress of women into infertility after the onset of the menopause.  Females of all other animal species, including primates, remain potentially fertile until they die, even when kept alive in zoos well beyond their natural life spans.  When the menopause arose is difficult, if not impossible to judge, but the advantage of surviving grandparents, especially grannies released from the burden of child-bearing and care, is huge.  They carry knowledge from two generations or more before the lives of their descendants, and they have the time to confer it on children.  Once grandparents became common members of families, effectively they would have doubled the potential for teaching and learning.  That has immense importance for human survival and development.  In 1990 I witnessed this in action in a remote and war-torn part of Eritrea.  There was a drought worse than any since 1918, and villagers were frantically searching for drinking water for themselves and their livestock, to the extent that they were felling giant baobab trees, more than 300 years old, to get to their water-rich inner core.  While we were attempting, with little success, to advise a group on where to dig a new well a young boy with a large camel arrived.  On it was a couple well into their 80s.  They directed attention to a particular spot, digging resumed, and after 2 hours water was struck. That place was where the couple remembered a well being dug in the great drought of 1918.  It is possible to get some idea of when the possible influence of grandparents arose by finding evidence about age distribution in ancient populations.  The further back in time, the more incomplete are human remains.  However, teeth have the highest of all survival chances, and the do carry evidence of the age of the person who chewed with them, from the wear patterns and the presence or absence of late-erupting teeth (Caspari, R. & Lee, S.-H. 2004.  Older age becomes common late in human evolution.  Proceedings of the National Academy of Science, USA, v. 101, p. 10895-10900).  Caspari and Lee’s work used more than 750 samples of  human teeth, dating back to some of the earliest hominids.  The measure that they adopted to assess onset of old age does not increase gradually into more recent times, but undergoes a remarkable jump around 30ka.  Interestingly, this coincides with the explosion of art of the highest quality in Europe.  Was it the oldsters who made that leap or was it their influence that opened up new horizons for their grandchildren.  Other than this remarkable possibility, the opening of culture as we know it is hard to explain.

Black Sea flooding put to test

In the mid-1990s, William Ryan and Walter Pitman of the US Lamont-Doherty Earth Observatory captured a much wider audience than is the normally the case for geoscientists, when they announced evidence from the Black Sea that seemed to confirm legends of the Flood in the Old Testament and the Epic of Gilgamesh.  They claimed that in early Holocene times, the Black Sea was a freshwater lake some 150 m below present sea level.   At the time, global sea level was below the threshold of the floor of the Bosporus, thereby isolating the Black Sea from the world’s oceans.  Yet sea level was rising inexorably as continental ice sheets melted back.  Around 8000 years ago, sea water flooded through the Bosporus to fill the Black Sea to its present level.  Evidence takes the form of submerged beaches and even possible townships (mounds similar to the tells in Turkey and Mesopotamia formed during long-term occupation by Neolithic to Bronze Age cultures).  Other features on the floor of the Black Sea are zones of large sand waves and signs of incision, ascribed by Ryan and Pitman to massive currents when flow began through the Bosporus.  The way in which such flooding might have take progressed is testable using hydraulic modelling, although the topographic parameters are complex (Siddall, M. et al. 2004.  Testing the physical oceanographic implications of the suggested sudden Black Sea infill 8400 years ago.  Paleoceanography, v. 19, PA1024, doi:10.1029/2003PA000903).  The work of Siddall and colleagues suggests a flow rate of 60 thousand m³ s^-1, about that of a river as powerful as the Brahmaputra (see Catastrophic erosion in Tibet, this issue of EPN).  That would have taken around 30 years to fill the Black Sea to its present level; far longer than the Biblical 40 days and nights, but quick enough to force large-scale migration and to live on in legend.  The model fits with the seabed sand waves and channelling, and being based only on known topography and post-glacial sea level rise, rather than the myths, it carries weight scientifically.  However, little is known about the way in which young sediments in the Black Sea basin formed, and proper documentation awaits their coring..

See also:  Schiermeier, Q.  2004.  Noah’s flood.  Nature, v. 430, p. 718-719.