  The last few million years on planet Earth have witnessed two remarkable
phases of hominid development, starting with a phase of biological evolution
characterised by rather rapid increase of the size of the brain. This has been
followed by a phase of even more rapid technological evolution and concomitant
expansion of the size of the population, that began when our own particular
`sapiens' species emerged, just a few hundred thousand years ago. The present
investigation exploits the analogy between the neo-Darwinian genetic evolution
mechanism governing the first phase, and the memetic evolution mechanism
governing the second phase. From the outset of the latter until very recently
-- about the year 2000 -- the growth of the global population N was roughly
governed by an equation of the form dN/Ndt= N/T*, in which T* is a coefficient
introduced (in 1960) by von Foerster, who evaluated it empirically as about two
hundred thousand million years. It is shown here how the value of this hitherto
mysterious timescale governing the memetic phase is explicable in terms of what
happenned in the preceding genetic phase. The outcome is that the order of
magnitude of the Foerster timescale can be accounted for as the product of the
relevant (human) generation timescale, about 20 years, with the number of bits
of information in the genome, of the order of ten thousand million. Whereas the
origin of our `homo' genus may well have involved an evolutionary hard step, it
transpires that the emergence of our particular `sapiens' species was rather an
automatic process.
