Wednesday, July 29, 2020

Biological Species & Natural Kinds

If I have one big idea it is that one can understand Platonic and Aristotelian ontology and metaphysics better (or perhaps at all) by comparing them with modern evolutionary biology and vice versa.  I think I began to understand Aristotle much better, after decades of reading the Physics and the Metaphysics, when I realized that many contemporary debates in the philosophy of biology were recapitulating problems already present in Aristotle. 
Two days ago, I grabbed a book off my self on the way to the toilet.  Some of my biological processes seem to require reading material.  Darwinism and Philosophy [ed. Vittorio Hösle and Christian Illies (2005)] included an essay by Michael T. Ghiselin.  The latter is most famous for his answer to one of the great questions of modern biology: what is a species?  Is it a natural kind, like oxygen in the periodic table of elements?  Is it a group of (potentially) interbreeding organisms like elk?  Is it merely a customary grouping, like red pieces of laundry?  Each of these answers has its proponents. 
Ghiselin’s answer is that a species in an individual.  If that makes no obvious sense, you are in good company.  It made no sense to me until, sitting on porcelain and doing God’s work, I realized that Aristotle had joined the conversation.  By the time I finished the paperwork and returned to my desk, I was convinced that I understood Ghiselin’s argument and I was convinced that he was right. 
An individual is something that is located in space and time and, for that reason, has a history.  The Garmin fitness tracker on my left wrist is an individual; this one is mine, not somebody else’s.  The same is true of my wrist and me.  I had a beginning in time and my being traces a continuous path from that time and place to now.  The same is true of Homo neanderthalensis.  That species had a beginning, spread out across portions of the globe, and came to an end. 
Natural kinds are not located in time and space the same way.  Gold is gold wherever it occurs, whether it was dug up in California or discovered on Mars or produced in a supercollider.  As opposed to individual lumps of gold, gold has no history; it has only essential properties. 
Aristotle covered this same ground.  There are things that have properties-horses for example-and there are the properties that such things have-shape, weight, and species forms.  The things that have properties would seem to be the things that are real.  A horse can change color (age happens, even to Seabiscuit) and yet remain a horse; its color exists on in the horse and the color ceases to exist when the color has changed. 
This suggests one answer to the question: what is most genuinely real?  For the purposes of biology, at least, it is the individual organism.  From the horse one can abstract downward to its properties (color and size), its matter (meat and bone), and its parts (limbs and organs).  Likewise, one can abstract upwards to its species form, which links it to the other horses.  All of these are abstractions because they exist only in analysis; they depend for their reality on this here animal. 
Aristotle might have rested with this had he not inherited the central problem of Greek philosophy.  What is most real should be what is most knowable.  It is not clear that I can know anything about individual organisms.  Is she short or tall, young or old, alive or not.  On the other hand, I can know that horses are mammalian quadrupeds in a rather more secure way. 
Ghiselin’s view that species are individuals seems to address this problem.  If species are not eternal, they are not knowable in the same sense that triangles are knowable.  They are at least more knowable that a particular horse.  His account points, however, toward a solution to the problem. 
Ghiselin does not deny that the species as natural kind account points to something real.  The species horse is an emphatically real thing: there are lots of horses.  The natural kinds horse, mammal, etc., are real in so far as horses really are horses and mammals.  He just insists that natural kinds of this sort are properties of individual species. 
A good indication that we are on the right track is that our account to solve problems that once seemed too difficult.  I was raised, intellectually speaking, in a hotbed of natural rights theorists.  Under the guidance of Harry V. Jaffa, we took the Declaration of Independence very seriously.  In that I have not wavered. 
The Declaration speaks of the Laws of Nature and of Nature’s God.  Inferred from such laws is the self-evident truth that all men are created equal in so far as they enjoy certain unalienable rights.  Here I understand “men” to mean human beings.  My colleagues who reject evolutionary biology do so on the grounds that undermines confidence in the existence of a stable human nature that can bear such properties as unalienable rights. 
In the evolutionary scheme, species seem to differ not in kind but only in degree.  For example, lions and tigers can mate and produce ligers, hybrids that are not capable of having offspring.  This means that the two species share a large percentage of their DNA but not enough to produce a lineage.  So lions and tigers differ, genetically, only in degree.  Species as individuals emerged from common ancestors and so differ only in their unique history and genomic families.  From that point of view, the critics appear to be correct. 
Not so fast.  Individual species also present real differences in natural kind.  A particular lion may be so much a tiger, genetically speaking, and he may be bigger than more aggressive than another male lion when he squares off on the field of reproductive competition.  He is, however, no more a lion than any one of his competitors.  Socrates, Aristotle insists, is no more a man than any of his interlocutors. 
To bring this back to the Declaration, allow me to indulge in a little science fiction.  Suppose we encounter living organisms on another world.  Assume that these organisms emerged historically through the same evolutionary processes as life on earth.  We will find there no organisms that belong to the same species as those on our planet, at least in Ghiselin’s terms.  None of those species will have a common history with any of our species.  Yet the fact that we recognize them as living organisms means that they do share something vitally important.  The living organism is a natural kind.
Now suppose that we encounter Vulcans or something of that sort.  Green blood and distinct biological history notwithstanding, they are capable of symbolic communication and moral responsibility.  They can recognize mutual obligations between themselves and us newcomers.  They are capable of making contracts.  Are they “men” as the Declaration means that term?  Of course.
Human beings are certain kinds of beings.  Our species has its unique biological history, just as do individuals and populations of individuals within that larger individual that is our species.  While we are diverse in many respects, no son or daughter of humankind is more an organism, or a mammal, or a human being than any other.  I find the distinction between species as individuals and natural kinds to be worth thinking about.