I think Benjamin Franklin (probably as "Poor Richard") did a humorous piece about this.
Note that Charles Darwin, having married his first cousin, Emma Wedgwood, the niece of Darwin's mother, had children with two parents, four grandparents, but only six great-grandparents. Lots of similar cases can be cited.
Of course, we are all related. Even the chipmunk in your yard, the spiders in your house, the fungus on your trees, the grass in your lawn, etc., etc., are distant cousins of yours.
Laurent Hodges
________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of brian whatcott [betwys1@sbcglobal.net]
Sent: Saturday, September 11, 2010 9:49 PM
To: Forum for Physics Educators
Subject: [Phys-l] H. Sapiens
There are less than 8 billion people presently on Earth.
Supposing a generation time is 25 years, and supposing the
H.Sapiens line is only 100, 000 years old as a species
then one can suppose there have been 4000 generations of this species.
since 1.004 ^4000 ~=8.6 billion, then we can suppose that over the long
haul,
each generation represents an effective multiplication of 1.004 at most
in the population.
By this reckoning, in 25 years, 2 people become 2.008 people on average.
This seems to mean that two people can usually produce 2 children
who survive to maturity, with a small chance 0.8% of producing three
children who survive to reproduce.
These numbers do not seem extravagantly controversial.
However, when 2.08 kids count two parents, they can count 4 grandparents,
and 8 great grand parents so that the genetic inheritance doubles for
each generation.
It seems that such doubling allows for a maximum of just 33 generations
of independent genetic contributions, according to the equation 2^33
~=8.6 billion.
This seems to imply just 33 X 25 years before all the possible genetic
inheritance is exhausted. One can easily be led to suppose that
the entire world population is related to all others as not very distant
cousins.
Any insights?