Introducción

Th roughout this chapter so far, and Chapter 8, I have been writing about biolog- ical kinds. Gold is a kind, and I have been writing as if horse, dog, mammal and

chordate are all kinds as well. One thing that has emerged in the foregoing dis- cussion is that the criteria for including something in a biological kind are very diff erent from the criteria for including them in a chemical kind. Something is included in a chemical kind in virtue of a characteristic it currently has. Pheneticists such as Sneath and Sokal propose that we take a similar approach to classifying living things, but this approach seems to be beset with problems. Moreover, chemical kinds are free from vagueness – something is either gold or it is not – whereas biological kinds are vague, and seem to be inescapably so. Th is is the case whether we take a phenetic or a cladistic approach. One moral we might draw from this is that when we use the term “natural kind” we mean diff erent things in diff erent cases: that is, the sense in which a biological species is a natural kind is not the sense in which a chemical element is a natural kind. Th is moral is drawn by David Hull:

From the beginning, a satisfactory explication of the notion of a natural kind has eluded philosophers. One explanation for this failure is that the traditional examples of natural kinds were a mixed lot. Th e three commonest examples of natural kinds have been geometric fi gures, bio- logical species, and the physical elements. By now it should be clear that all three are very diff erent sorts of things. No wonder a general analysis, applicable equally to them all, has eluded us. ([1978] 1994: 208) Hull proposes a radical solution to this problem, which was also proposed by Michael Ghiselin (1974). Rather than consider species to be kinds at all, we should consider them to be individuals.

At fi rst sight, this seems like a very strange suggestion. Surely, you might think, horses (say) constitute a kind, whereas Black Beauty is an individual horse? However, Ghiselin and Hull are not saying that Black Beauty is not an individual. Th ey are saying that the same reasons we consider Black Beauty an individual justify calling the species Equus caballus an individual as well. Th ere seems to be no problem in an individual being part of a bigger individual. You have individual cells in your body, which are part of you, but you are no less an individual.

What are the grounds for calling a species an individual, and not a kind? Recall that the criteria for calling something gold appeal to properties that that thing currently possesses. If it has atomic number 79, then it is gold. Th is means that if something with atomic number 79 were to appear at any time, anywhere in the universe, it would be gold. If all the matter of atomic number 79 were to disappear, there would be no gold. If any were to subsequently appear, it would be gold. Moreover, if scientists synthesized atoms of atomic number 79 in a laboratory, they would be gold atoms. Th us, the kinds in chemistry are spatio-

temporally unbounded. Th is is a straightforward consequence of the fact that whether something is gold or not depends on whether or not it currently possess

such-and-such a property. By contrast, on the cladistic conception of taxonomy, which is the currently orthodox view, it is a necessary condition for something being a member of the species Equus caballus that it share a common ancestor with all and only members of that species. Th us, no matter what properties a creature possesses – no matter how much it looks like a horse, walks like a horse, or neighs like a horse – if it does not have the ancestry common to horses, it is not a horse. Th is is a straightforward consequence of accepting that being a monophyletic group is a necessary condition for being a species, even if it is not a suffi cient one. Th us, if the horse species goes extinct, but creatures that are exactly the same as them come into existence later on, those creatures will be not be horses. Species, unlike chemical elements, are spatiotemporally bounded.

Ghiselin and Hull argue that this spatiotemporal boundedness makes species more like the things that are undoubtedly individuals, than like the things that are undoubtedly kinds. A person is an individual. But people go through many changes in their lives. It is perfectly conceivable that there is a fi ve-year-old somewhere who is more like you when you were fi ve than the present-day you is like you when you were fi ve. But this would not for a moment lead you to doubt that you are the same individual as the fi ve-year-old you, and that that other person is not the same individual as the fi ve-year-old you. Similarly, if a scientist were to make an exact copy of you, it would not be you. Th at would be the case even if the copy were a genetically exact replica, for we all know full well that a pair of identical twins is two people, not one. (Much science fi ction plays with the idea of cloning, and exploits a fear that being cloned would somehow blur the boundaries of individuality. Th e authors, or their audiences, seem to have forgotten what we all know about identical twins.) In this respect, then, species seem to “behave” more like individuals than like kinds.

Th ings are perhaps not as simple as this suggests, however. Imagine a Jurassic

Park-type scenario. Assuming for the sake of argument that the logistical prob-

lems are as easily surmountable as Michael Crichton glibly assumes that they are, would we call these creatures Tyrannosaurus rex and so on? If we do, are we not accepting that, contrary to what I said above, a species could go extinct and then come back into existence again? Even with the arguments I have just sum- marized, there is still some reason to say: yes, they are members of the species

Tyrannosaurus rex. Th e hypothetical scenario in Crichton’s novels is that the new creatures were produced using

dna

from actual, undoubted tyrannosaurs. So there is a causal connection between the undoubted tyrannosaurs and the new creatures, albeit a more tenuous causal connection than in the normal case. Similarly, if your sperm or eggs were frozen and used to produce a baby aft er you were dead, we would still probably say that you were the baby’s father or mother. By contrast, if we synthesized gold atoms out of atoms of some other element, it would surely not make any diff erence whether those atoms had in turn been synthesized out of gold atoms or not. Either way, it would still be gold.

Th ere does not have to be any causal connection whatsoever between the new atoms and any previously existing gold atoms.

Let us press this issue a little further. Suppose that, instead of using

dna

from tyrannosaurs, the scientists synthesized

dna

of the right kind using the raw materials cytosine, guanine and so forth. Would we now say the new creatures were tyrannosaurs? Maybe; maybe not. On the one hand, the causal connec- tion that was there on Crichton’s scenario is no longer there. On the other, the scientists have copied tyrannosaur

dna

, so there is still a causal connection, albeit one that is even more tenuous. Th e causal connection goes via the knowl- edge and the intentions of the scientists. For the causal connection to be totally severed, we would need a situation where new creatures exactly like tyran- nosaurs came about, which were neither born of undoubted tyrannosaurs, not made by scientists using their knowledge of the tyrannosaur genome. Perhaps they could evolve by some process of massive convergence and/or coincidence. Or perhaps scientists, without intending to, could produce

dna

that was just like tyrannosaur

dna

. Note, however, that these complicated questions do not arise with gold. Th e criterion for being gold can be applied to new atoms that are formed totally by chance, or by natural forces without any human interven- tion whatsoever. So perhaps the very fact that these complicated questions arise gives further support to the view that species are not kinds.

Let us return to the cloning issue, however. I deliberately avoided saying

how the scientist makes this exact copy of you. On the usual understanding of

“cloning”, it is done by taking some

dna

from you, just as in Jurassic Park. We would, for that reason, have no problem saying that the new person produced was the same species as you. But the general consensus (certain science-fi ction writers apart) is that the new person is not you. Th ere is, once again, a whole host of possible variations on this theme. Suppose an atom-by-atom replica is produced while, at exactly the same time, you are annihilated. Is that new person you? Many people would probably say yes, and at least the example would give us pause in a way that the cloning example does not (or at least should not) give us pause. But if I am right that in the cloning case the new person is clearly not me, then the requirement for being the same individual is much stronger than mere causal connection of some kind. In fact, the causal connection between you and a clone of you is of exactly the same kind as that between the original tyrannosaurs and the new creatures. Perhaps some other scenario where the causal connection was weaker than in the Crichton story would lead us to say that the new creatures were not tyrannosaurs. And it is likely that in both the individual person case and the species case there are borderline scenarios where we would fi nd it diffi cult to decide either way. Gheselin and Hull have made a good case that species do not behave exactly like the things that are undoubtedly kinds. But, I suggest, perhaps they do not behave exactly like the things that are undoubtedly individuals either.

In document Tesis presentada por. Karla Jazmín Torres Rodríguez. para obtener el grado de MAESTRA EN DESARROLLO REGIONAL. Tijuana, B. C. (página 37-41)