UNCG Biology 589a — Darwin and His Critics

Species and “Essentialism”

Darwin’s book is about the origin of species. In a rough-and-ready sense, a species is a kind of animal or plant. But does this definition really help, to say that a species is a kind of animal or plant? What does it mean to say that two things are “the same kind,” or that two other things are not “the same kind”?

The answer to this question—the question of what a “kind” or “species” is—has been one of the most persistent problems in the history of science and philosophy. The older view (this could have been included in Bowler’s list of older world views) was something called “essentialism.” According to essentialism, all things of the same kind—all chairs, dogs, humans, stars, horses—share a common essence. All chairs, for example, have an essence we might call “chair-ness,” and that’s what makes them chairs. All humans have “human-ness” (human “nature”) as their essence. The essence of a kind can be thought of as an ideal model on which all the real examples are based. An essentialist might say that every real chair is just an attempt to capture the idea of perfect “chair-ness.” All real chairs are different, of course, so no chair perfectly captures this essence. But what makes all chairs one kind of thing (what makes them all chairs, as opposed to tables, or doors), is that they all capture, even if only incompletely, the essence of chair-ness.

The Greek philosopher Plato is one of the most well-known essentialists, and his “Allegory of the Cave” from Book VII of The Republic is the most famous early exposition of the essentialist view of kinds. According to the Allegory of the Cave, true knowledge is knowledge of the essences of things, not of the varying individual things themselves, because variation is the result of accident (local circumstance) rather than essence. If you are interested in chairs, you should not study individual physical chairs, what you should study is the Ideal Chair, the essence of chair-ness. The individual chairs we see around us are like shadows cast on the wall of a cave by the Ideal Chair, which we cannot see. The shadows are imperfect and incomplete; true knowledge comes from an understanding of the essence that is casting the shadows. An excerpt from the Allegory of the Cave appears below.

Essentialism is of importance to us because it was not only the common way of understanding “kinds” of inanimate objects, like chairs, tables, and stars, but it was also the common way of understanding kinds of living things (biological species). The second and third quotations below present essentialist views of biological species. One is from the American essayist Ralph Waldo Emerson, and the other is from the French naturalist Georges Buffon. Keeping in mind the date of the Origin of Species, notice when these two passages were written. The modern evolutionary view of biological kinds (species), deriving from Darwin and Wallace, is sometimes called “population thinking,” and it is a direct challenge to essentialism.

Plato’s “Allegory of the Cave”

[Plato, the teacher, says,] “take the following parable … as a picture of the condition of our nature. Imagine mankind dwelling in an underground cave with a long entrance open to the light across the whole width of the cave; in this they have been from childhood, with necks and legs fettered, so they have to stay where they are. They cannot move their heads round because of the fetters, and they can only look forward, but light comes to them from a fire burning behind them higher up at a distance. Between the fire and the prisoners is a road above their level, and along it imagine a low wall has been built, as puppet showmen have screens in front of their people over which they work their puppets.”

“I see,” he [Glaucon, the student] said.

“See, then, bearers carrying along this wall all sorts of articles which they hold projecting above the wall, statues of men and other living things, made of stone or wood and all kinds of stuff, some of the bearers speaking and some silent, as you might expect.”

“What a remarkable image,” he said, “and what remarkable prisoners!”

“Just like ourselves,” I said. “For, first of all, tell me this: What do you think such people would have seen of themselves and each other except their shadows, which the fire cast on the opposite wall of the cave?”

“I don’t see how they could see anything else,” he said, “if they were compelled to keep their heads unmoving all their lives!”

“Very well, what of the things being carried along? Would this not be the same?”

“Of course it would.”

“Suppose the prisoners were able to talk together, don’t you think that when they named the shadows which they saw passing they would believe they were naming things?”

“Necessarily.”

“Then if their prison had an echo from the opposite wall, whenever one of the passing bearers uttered a sound, would they not suppose that the passing shadow must be making the sound? Don’t you think so?”

“Indeed I do,” he said.

“If so,” said I, “such persons would certainly believe that there were no realities except those shadows of handmade things.”

“So it must be.”

. . . . . . . . . .

“Then we must apply this image, my dear Glaucon,” said I, “to all we have been saying. The world of our sight is like the habitation in prison, the firelight there to the sunlight here, and the ascent [through the tunnel and out of the cave] and the view of the upper world is the rising of the soul into the world of the mind.”

—Plato, about 360 BC, The Republic, Book VII (transl. W.H.D. Rouse)

Buffon on the “Internal Mold”

There is, in nature, a general prototype in each species upon which each individual is modeled, but which seems, in realizing itself, to be altered or perfected by circumstances. So that, relative to certain characteristics, there is an unusual variation in appearance in the succession of individuals, and at the same time a constancy in the species as a whole which appears remarkable. The first animal, the first horse, for example, has been the external model and the internal mold upon which all horses which have ever been born, all those which now exist, and all which will arise, have been formed. But this model, which we know only by its copies, has been able to be altered or perfected in the communication and multiplication of its form. The original impression subsists in its entirety in each individual, but although there might be millions of them, none of these individuals is similar in entirety to any other, nor, by implication, to the impressing model.

—Georges Buffon, 1753, Histoire Naturelle, v. 4 (from Sloan 1987: 121)

From Emerson’s “Nominalist and Realist”

In countless upward-striving waves
The moon-drawn tide-wave strives;
In thousand far-transplanted grafts
The parent fruit survives;
So, in the new-born millions,
The perfect Adam lives.
Not less are summer-mornings dear
To every child they wake,
And each with novel life his sphere
Fills for his proper sake.

—Ralph Waldo Emerson, 1844, “Nominalist and Realist”