From: vanweer@ecf.toronto.edu (VANWEERDENBURG NICHOLAS JOHN)
Subject: Re: Mark's Laws of Biology
Organization: University of Toronto, Engineering Computing Facility
Date: Sat, 9 Jan 1993 03:00:05 GMT

In article <fargher.726454093@unixg.ubc.ca> fargher@unixg.ubc.ca (Robert Fargher) writes:
>In <1ichi8INNojs@uwm.edu> markh@csd4.csd.uwm.edu (Mark) writes:
>
>>I propose these very general laws on a linkage between procreation, aging and
>>complexity:
>
>>(1) In all species, over the long term, the average birth rate is equal to the
>>    average death rate.
>
>>Are laws (2), and (3) consistent with actual biological data? ((1) is
>>obnviously valid).
> 
>   Hmm. Your law (1) is just as obviously invalid in my eyes.  First off,
>consider Homo sap; our birth rate has significantly exceeded our death
>rate for many moons, with punctuations (the Great Plague, the Black Death,
>WWII).  I don't have the data handy, but the doubling time of humans has
>greatly decreased over many centuries.
>  Considering other organisms, a few seconds thought will convince you
>that (1) cannot be true.  If the birth rate equalled the death rate, no
>species would ever go extinct.
>-- 
>Robert Fargher  fargher@unixg.ubc.ca |  The number of things that I know

Actually, he does say average, and as far as I know everyone who is born,
dies.  So even if the population grows, the average birth/death rates will 
often be reasonably close, depending what period the average is taken over,
and growth rate to life span ratio.

Take whole life span of a species.  Everything that was born, died.  Thus
average birth rate must equal average death rate.

Now, if there was an exceptionally high population growth rate, the averages
wouldn't be anywhere near equal for a short period.  However, for a longer
period ( say > 1 generation ), they would get closer.  How close would 
depend on the growth rate. As for humanity, with a doubling rate of about
20 years, births would only outpace deaths by significantly less than
5% to create this, which could be considered almost equal.  However, for
a newly created bacteria, birth to death rates would never be anywhere near
equal until growth rate stops ( extinction ) or slows down enough such that
the population that has lived and died since origin is much greateer than the
population currently alive.  This assumes an exponential growth rate of a value
value typical of bacterias ( doubling in minutes or hours ).  Basically, 
whether BR and DR are near equal is dependent upon:
      1) growth rate
      2) life span/ birth rate proportionality. 
           ( If members of a species never die, then growth rate is 
           irrelevent- the B-rate is infinitely greater than D-rate!! )
      3) period average taken over.     

Funniest point:  all extinct species have EXACTLY the same birth rate and
                 death rate over there entire existence ( long term! ).

Thus point (1) in above post is wrong as a generality, correct in some cases,
and can be either correct or incorrect in some cases depending on how you
define 'long term'.  My apologies for some of the disjoint logic- I changed
my mind on how to say what I was going to say at points, and made a bit of 
a mess, but I can't be bothered editing in vi ( I don't know how! ).   
-- 


------------------------------------------------------
Nick Vanweerdenburg
Newsgroups: talk.origins