what is a species (was ploidy)

Joe jshaw@opuntiads.com
Wed, 12 Dec 2007 19:07:42 PST


One of my favorite topics to write about is "what is a species" and all of our (human) various efforts to answer the question.  Sometimes complicated subjects eventually lead back to bulbs, so bear with me.   I enjoy reading John Hawks Weblog on Anthroplogy.  Recently he wrote:  

There will never be any tidy solution to the species problem, because all species have unique evolutionary histories and constraints. Given these difficulties, the species status of archaic Homo populations is basically an intractable problem. That is, I am happy to suggest that archaic Homo populations correspond to classical subspecies, and as far as I know, no evidence strongly contradicts that position. But I can recognize that some people will never agree with this assignment. And from the perspective of their evolution, it just doesn't matter. Evolutionarily important gene flow occurs between mammal species, subspecies, and populations.

The relevance of this topic for botanists is that is suggests that our attempts to definitively delineate  plant species is nearly impossible.  The various plants of the world will interbreed or not, and by doing so establish their own genetic definitions of species.  Humans have not settled on a single definition of a species for plants, much less subspecies or genera, but this has not stopped plant species themselves from going about their business.  Oaks don't interbreed with pines, a fact easily observed and verified.  However, in South Africa, who can say what apparently unrelated Cape bulbs sometimes successfully exchange pollen and produce viable progeny that backcross; if such an event happens one can ask if the involved plants are  a single species or distantly related subspecies  The categories of Linnaeus just don't work sometimes.   

The human genome project (and other genome projects) has produced enormous amounts of information, some of it even being extracted from humans that lived over 30,000 years ago.  These humans ("modern" and Neanderthal types) DNA projects are of are of great relevance to botanists because the human-based projects are relatively well funded in comparison with plant DNA projects.  Therefore, the human studies provide much information about how to procede (when funding does become available) as well as how to recover and handle ancient DNA.  It will soon be possible to sequence entire plant communities that may have been covered in rock, ash, mud, or water many thousands of years ago, and which contain ancestors of modern bulbs.  Possibly, the human genome projects will show ways to interpret and handle such DNA information (including tiny odd chromosomes).  

Speaking of Linnaeus (as was discussed on this email list earlier this year), this year marks his 300th birthday and there are several Web pages devoted to articles about him.  Some of the articles are free and others require registration or a subscription.  

Science Magazine, Happy 300th Birthday (cute slide show, free, about Linnaeus, plants, and our diet)

Science Magazine, Happy 300th Birthday (opinion piece, free)

Nature Magazine, Linnaeus in the information age (free)

Nature Magazine,  Linnaeus at 300 

For the Love of Plants (all about Linnaeus and plant names, and plant descriptions)




Joe Shaw

Conroe TX

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