Evolution Discussion

Keith Robison robison1 at husc10.harvard.edu
Fri Feb 18 08:38:38 EST 1994

brianf at med.uvm.edu (Brian Foley) writes:

>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?
>	You might just as well make up a number yourself, because there are
>a number of unanswered problems to solve before one could even start to 
>make and educated estimate:
>	What is your definition of "species" going to be?  The criteria 
>used to define mammalian species do not work for bacterial species. 
>	How are you going to estimate the number of species of life forms 
>that are not of interest to man?  Humans are mammals so we have a pretty 
>good idea of the number of other mammals on earth, but we have really 
>paid no attention to how many types of microorganisms might inhabit all 
>the different ecosystems on earth.  There are known to be many "species" 
>of bacteria that cannot yet be cultured in the lab.  Dr. David Ward at 
>Montana State University has made some estimates of the number of 
>bacterial species in one Yellowstone hot spring.  He used PCR to amplify 
>rRNA from bacteria collected on a filter paper and found that there was 
>far more variety than had been expected.

There is a rather stunning (IMO) illustration of the undercounting of
microbial species in the phylogenetic trees generated by the
Ribosomal Database Project (gopher to gopher.rdp.uiuc.edu or
ftp to ftp.rdp.uiuc.edu or see first article in one of the two
January 1994 J.Bacteriology -- I forget which).  Some of the
bugs on this tree are recent isolates identified only by
where they were found and a serial number.  One clade containing
only 4-5 such isolates forms a new archean group on at
least the _phylum_ level -- this group doesn't join any named
species until nearly the root of the archea's!!!!!  There is
an awful lot out there that we haven't yet looked for!

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

krobison at nucleus.harvard.edu 

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