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.


  1. This was a fascinating read. But I have questions. You suggest that a horse is a real thing and that its properties are less real, because if the horse disappears, they go away, but if they go away, the horse remains. But what is a horse? If all his properties go away - his shape, size, color, personality, etc, all of them go away. WHAT still exists? How would you describe such a hirse and how would you know it was a horse and not a lion? Is it possible that - if a horse lost all its properties it would not exist anymore and if so, might it not be any more real than any property?

    And then there's the realness of the properties. Are things less real because they only exist temporarily? Even if the horse's color changes, wasn't the horse really black at least for a time? Wasn't his shape his shape? And when the horse goes the way of Sagan's star stuff and he doesn't exist anymore - and there is no one left to remember him - doesn't he become something that only temporarily existed too?

    1. One among many reasons that I love you, Miranda, is that you ask me hard questions. Obviously individual creatures such as horses or human beings cannot exist without properties. My hair is not the same color as it was in my wedding photographs, but my eyes are the same color and I am still, I hope, a Homo sapiens. Hair color is accidental; species form is essential in so far as I cannot continue to exist in this world without continuing to be human.

      Aristotle argued that these properties are less real (or less substantial) because they exist only in some substance. As that famous Aristotelian, the Cheshire Cat suggests, a cat without a smile is impossible. A smile without a cat, or some other smiling creature, is not.

      The key idea in Aristotle's metaphysics is the idea of substance. The iron in an iron bar is the substance which stands under (sub-stands) possible changes. Heated from cold and blue to red and hot, it remains iron all the time. Color and temperature exist on in such things. Iron and horses do not exist in anything else in that way.

    2. And one of the many reasons I am grateful to you is that you always answer them so thoroughly.

      What you say here makes sense. And I do understand and agree with with your explanation of the difference between properties and substance.

      But I'm still struggling with some things.

      What about a species that evolves? At some point, a cell or cells or some kind of genetic code that came from one species would have had to have mutated enough to make one species become another. But did any evolving organisms stop existing during these changes?

      Couldn't you really still exist in this world if you stopped being human and instead became human+?

      On the second part:

      There are restrictions on slavery in the Tanakh, that forbid Jews from ever making slaves of each other and also forbid the forcing of indefinite servitude of others. God's people are not to treat each other as they were treated in Egypt and I do see evidence that God disapproves of the type of slavery and treatment the Egyptian slavemasters engaged in.

      And in both Christian scriptures you have arguments for equality and compassion towards others.
      The idea that everyone has fallen and everyone can be redeemed are the kinds of principles that refute certain ideas of superiority.

      Plus, the argument that the founding fathers make is one that draws on religious authority. So if the question is one of confidence, you move from one that's this god-backed, powerful statement that doesn't just argue that people are capable of entertaining ideas like politics and processing concepts like rights, but that there is an inherent moral obligation to respect these rights.

      I wish there were something stronger in arguments from nature. Because I would love a powerful argument, based on biology, that made the case that people were entitled to life and liberty. Not just that protecting these things might make cooperation or trade easier.

      I would like to be able to point to something in nature that showed that when the Nazis were throwing babies into ovens, they were doing something evil and appalling, not just making themselves less attractive trading partners. But I have trouble finding any basis of this kind of concept in nature alone.

    3. Your comment here is very rich and I will have to make more than one response. To begin with the first point.

      "What about a species that evolves? At some point, a cell or cells or some kind of genetic code that came from one species would have had to have mutated enough to make one species become another. But did any evolving organisms stop existing during these changes?"

      Dogs and wolves and coyotes can all interbreed, producing wolf dogs and coy-wolves (a very interesting subspecies). Speciation has not yet occurred. Lions and tigers can produce offspring (ligers and tigons) but the offspring are rarely if ever fertile. No power to produce a lineage means that speciation has occurred. It is not that the ancestor species ceases to exist when this happens, anymore than my Father ceased to exist when he sired two sons.

    4. Thank you very much for your response. I think I may understand what you are saying, but I may not, so, for clarity, I'm afraid I am going to have to ask you how babies are made. Say we have a coyote and a wolf. And these two mate. You'd have, in the beginning, a coyote egg cell - a cell of a distinct and specific species. Which would would then be fertilized by a wolf a sperm cells - a cell of a distinct and specific species - and together they would form a zygote. Neither the egg cell, not the sperm cell are ancestors of this zygote. They're part of it. So you have these coyote cells that are no longer coyote cells. They've ceased from being cyote and ceased from being a wolf. And changed into something else. The cells still exist. Or am I misunderstanding?

    5. "Coyote" and "wolf" are labels that we use to keep track of distinct populations of canine animals. Coy-wolves, a relatively new population of canines currently colonizing a lot of major metropolitan areas, are cross-breeds. Any C-W has ancestors that include all the wolves and coyotes that came down to the first C-W ancestors.

      If coyote and wolves and dogs can easily interbreed, then they are not in fact "distinct and specific species." They are distinct populations that belong to one species. The same is true of Norwegians and Eskimos. Genetically, one coyote differs from another by degree X and from a wolf by degree X + n.

      Does that mean that species aren't real? Hardly. None of the species we mention mate with bears despite the fact that the latter are, genetically speaking, just really big dogs. Over time, the genetic composition of a population will change. When two populations are separate for long enough, genetic changes will accumulate to the point that interbreeding is no longer possible. Then speciation has occurred.

      I once enjoyed watching bear cubs and wolf cubs play together, before Mama bear and the wolf baby sitter put a stop to it. Bears and wolfs have a common ancestor, but they are no longer the same species.

    6. Thank you. I appreciate the correction and I knew better than to start trying to talk about things I don't enough enough about.

      But still, at some point, if speciation occurs, doesn't there have to be a moment at which something that was not a part of one species becomes part of it? If the change is in whether or not one population can breed with another, wouldn't this still have to be true of the individuals in the different populations too?

    7. I have made a career out of talking about things I don't know enough about. It is a good way to learn.

      I am a little bit confused by the idea of something (an individual organism?) becoming part of some species. All dogs, coyote, and wolves are the offspring (over many generations) of a common ancestor species that lived at some point in the past. As that species spread out, different populations adapted to different environments. That, and random genetic shifts in geographically separate locations explains the difference in the three subspecies. Because the genetic differences are, apparently, relatively modest, the three populations can still interbreed. Individual wolves do not evolve. Each cub is born with a mostly fixed genetic inheritance. The populations evolve over time into more or less different forms.

      When a horse and donkey interbreed, the offspring is almost always male (as I seem to remember) and infertile. Since the two progenitors can produce one offspring but not grand offspring, they cannot contribute to a lineage. Speciation has occurred. The mule has as ancestors the horse and donkey and all the ancestors that the parents had.

      The same is true of a lion and a tiger, who can produce a liger or a tigon, depending on whether the lion was male or female. If you want to see an example, Google "Hercules the Liger". He looked like a giant calico cat. Hercules did not become part of a new species because ligers cannot produce a lineage. Like many individuals of any species who are incapable of breeding, he is a dead end twig on the feline evolutionary tree.

      Mules are remarkably strong evidence for the theory of evolution by speciation. Human beings and Neanderthals once interbred, something we now know from genetic analysis. Some Neanderthal DNA remains in the human population. That explains my great uncle Roy.

      Though I know of no experimental confirmation, I assume that Homo sapiens cannot interbreed with chimpanzees, Uncle Roy not withstanding.

  2. On this part:

    "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."

    I don't think they're wrong. There's a difference between a strong declaration and belieg that human rights are inherent and the suggestion that, perhaps, something in nature might make the rights of human beings worth thinking about. One invites strong prohibitions against violations. The other allows the possibility of human rights violations being perfectly acceptable.

    1. The distinction between species as individuals and natural kinds is worth thinking about for people like you and I who are capable of thinking. It helps clarify the strong declaration that "all men are created equal, that they are endowed by their creator with unalienable rights."

      That strong declaration does not rest on God's command, for a number of reasons. One is that if God disapproved of slavery, it is not so evident in scripture. It rests on God's endowment.

      My endowment is something I was endowed with. What is that? Is there a set of instructions written into my DNA or somewhere else: "do not deny X Y and Z to this creature"? Probably not. I was endowed with the capacity for moral responsibility and with a palate of moral emotions that constitute that capacity.

      Human beings are political animals. We cannot live fully human lives apart from one another. We have to engage, morally and politically, with others of a similar endowment. The character of that endowment, a capacity for self-government, provides instructions for how we should organize our commonwealths. That is the strong Declaration.

      As you point out, a horse is black when it's black. It's a horse so long as it's a horse. That looks pretty solid to me. Anthropoi are endowed with unalienable rights so long as they are anthropoi. Modern evolutionary anthropology strongly supports this account. Why does this bother you?

    2. Thank you for the explanation and patience.

    3. One thing you need not apologize for is provoking me into a mini-lecture. It is good for me and I enjoy it. If it sometimes seems like I am talking down to you, know that that is just me sorting out my own thoughts.

  3. I have never seen you talk down to any student. Quite the opposite. The thanks was genuine. I appreciate your corrections and encouragement equally. Thank you for both.