[Marxism] Anthro 101 and Apes and Monkeys

Mike Friedman mikedf at mail.amnh.org
Wed Dec 29 13:27:20 MST 2004


Disagree. Species is a taxonomic *concept*, an ordering device, like any 
other. The classic Biological Species Concept, which you both employ, is 
deeply flawed and highly controversial. Reproductive isolation is its 
fundamental criterion. Yet, interbreeding, is common among among 
closely-related and more distantly species, and resulting offspring are not 
always or even usually infertile. Among my snakes, I can get fertile 
offspring from any cross within the genus Lampropeltis. I can also get 
fertile offspring from crosses between some members of the genus 
Lampropeltis and the genus Elaphe. This interbreeding, or reticulation, is 
far more common among plants than animals. In fact a significant number of 
new plant species are thought to have arisen in this way. I don't think any 
biologist would state that it is "the second generation that defines a 
species." We also observe phenomena called "ring species" (no, it's not 
something out of Wagner), in which a population disperses and 
differentiates in a roughly circular pattern. Successive neighboring 
populations can interbreed, but when the ends of the ring meet, the 
populations have evolved to the degree that they can no longer do so. So, 
is this one species or two? The classic study on this was done right in 
California, on the salamander Ensatina. Finally, we have organisms that do 
not sexually reproduce, such as bacteria. If reproductive isolation is 
inoperative, how do you define species among such clonal organisms? Are 
Escherichia coli and Vibrio cholerae different species? There are those, 
including folks in my lab who are doing bacterial genomics, that say that 
the concept of "species" is inapplicable to bacteria and other suchlike 
organisms. Finally, reproductive isolation between species is ASSUMED in 
the case of most related species, which merely don't have the opportunity 
to screw each other because of geographic -- not biological -- isolation. 
What good is a species concept that isn't consistently applied? In my work, 
I use the also controversial Phylogenetic Species Concept, which holds that 
species are operationally defined as the smallest groupings of populations 
(sexual) or lineages (asexual) that are diagnosable by a unique combination 
of character states in comparable individuals. Such unique characters have 
become "fixed" in populations. Species are the basic units of phylogenetic 
analysis (making those funny evolutionary trees). Separate species exist 
when populations have diverged and don't interbreed: relations between 
species are hierarchical and not reticulate. Thus, the existence of such 
populations implies that there is NO gene flow between populations, but 
this doesn't imply that there are biological isolating mechanisms. 
Biological barriers to reproduction merely constitute just one more unique 
character state that enables diagnosis of a species. This concept, as I 
noted, is also problematic. But it enables me to conduct phylogenetic 
research, so I use it. As ornithologist Joel Cracraft put it, "the debate 
over how species should be defined will continue as long as people are 
allowed to think freely. Perhaps the argument is rhetorical, because every 
kind of organism presents a unique situation. It is possible that neither 
definition can be applied consistently in nature."



At 02:01 PM 12/29/2004, you wrote:
> > Here's the critical difference between species ( the category in Darwin's
> > title) and genus, order, family, the other taxa ( or is that phyla ?) etc.
> > The species defines the point at which interbreeding is limited. Different
> > genuses cannot interbreed. Different "sub-species" can interbreed. To say
> > Neanderthals are the same species as we are is to say we could interbreed
> > with them.
>
>Actually to nit-pick, species are defined at the point that any resulting
>offspring can still reproduce. You can actually cross breed related species,
>and this has been done with wolves and dogs, which produce sterile
>wolf-dogs, or more famously horses and donkeys, which produce sterile mules.
>
>It is the second generation that defines a species.





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