Evolution Discussion

Brian Foley brianf at med.uvm.edu
Tue Feb 15 16:54:02 EST 1994


wpainter at vnet.ibm.com wrote:

: What are the current estimates on the total number of species of plant and 
: animal life in the world today?
	Oops.  In my first response I did not notice that you were only 
interested in plants and animals, not fungi, eubacteria, archaebacteria 
and other life forms.  We do have fairly good estimates of plant and 
animal species diversity.  I don't have the number handy though...  
Anybody else?
	Or are you really interested in all types of organisms?

	A reference I do have handy is TIMESCALE by Nigel Calder.  It 
says that life is estimated to have started 4 billion years ago, the 
first photosynthesis was about 3.9 billion years ago, but the first 
bluegreen algaes evolved about 1.6 billion years ago and true plants 
(eukaryotic photosynthesis) evolved about 1.3 billion years ago.
	Thus, more evolution (2.7 billion years) took place before the 
arrival of "plants" than afterward (1.3 billion years).  Most of what 
people think of as evolution (the rise of the vertebrates) is only very 
recent, taking place over the last 0.5 billion years.
	It is likely that point mutations in DNA occurred at a higher 
rate in the first 1 or 2 billion years than it does today, because life 
evolved more accurate polymerases and better DNA repair machinery.  But 
it seems that the advent of sexual reproduction (about 1 billion years 
ago) has had a very large impact on the rate of evolution.

--
********************************************************************
*  Brian Foley               *     If we knew what we were doing   *
*  Molecular Genetics Dept.  *     it wouldn't be called research  *
*  University of Vermont     *                                     *
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