The Generative Conception of Species

John S. WilkinsUniversity of Queensland

What I’m going to do - focus on modern period, and particularly the French and English naturalists of the 18th and 19th Cs.

Outline

The Standard View of the History of SpeciesEssentialismTypologyFixism

Species as Similarity GenerationClassicalEarly Natural HistoryThe 18th and 19th Centuries

Conclusions

One Concept (in biology) many Conceptions

Run through an intensive fire of quotations (Churchill - intense versus intensive). This is because the standard view that I’m going to contradict is so well established that if you know it you may think I am making this up. We need them to establish what the early view of species actually was.

The Standard View: Essentialism

Mayrian essentialism:

“Western thinking for more than 2,000 years after Plato was dominated by essentialism. For Plato and his followers, variable classes of entities consist of imperfect reflections of a fixed number of constant, discontinuous eide or essences.

In 1859 Darwin introduced the entirely new concept of variable populations composed of unique individuals. Toward a new philosophy of biology 1988:15

The Standard View: Essentialism

Aristotle fingered as the culprit as well, by Simpson, Mayr and Hull.

Based on the use of eidos (= species or form)

The Standard View developed over a period of about 15 years, beginning with the centenary of the Origin in 1958

The Standard View: Typology

Mayrian typology:

Species types can mean species essences [TaNPoB, 407] separated by “bridgeless gaps”

Ideal morphologists’ archetypes can be descriptive

“Type” plays a role that is somewhat tangential to our story here, except that in conflating the notions of type and essence, Mayr managed to effectively relegate any use of types by pre-Darwinian biologists to evidence for his claim that essentialism was pre-evolutionary (and by implication that any modern biologist who used types was anti-Darwinian.

It should be noted this is not true, as even Darwin used types in his own systematics, and he had to make an exception from the equation for the ideal morphologists in the early nineteenth century.

The Standard View: Fixism

Mayrian fixism

These essences (natures, eide) are identical for all the members of a class or species. They are unchanging, all deviations being “accidents”. This philosophy, of course, made evolution impossible. [TaNPoB, 186]

Mayr and Hull hold that essentialism is the motive for fixity of species. Since essences cannot, by definition, change, if species had essences they wouold be fixed.

The Standard View

Essentialism ➔ Typology ➔ Fixism

Species have natures, definitions and are static

Darwin changed all that, with polytypy, history and individuality.

So, the issues that we will address today are that essentialism leads to fixism, that species have essential natures that can be captured by definitions, and that it all changed with Darwin. I’m going to argue that all three claims are in historical fact, false.

To pre-empt a problem that some may have philosophically, I should note that arguments against species essentialism in the modern literature do not rely upon this historical claim. As I will later assert, essentialism *is* a problem in modern literature, which I am going to arbitrarily set as 1900, for reasons I will give then.

What I am claiming here is that there is a shared conception, pretty much from Aristotle to the mid-19th century, about species that was shaken loose only when the discussions of heredity took place at that time, and species were reconceived in terms of heredity. Now there are people who use the metaphysical notions of essences, substance and form throughout this period to conceptualise species. This was the common heritage of western philosophy and it would be odd if they didn’t. What is odder still, though, is how *few* people apply these metaphysical notions, or anything much resembling them, to natural history. I’m going to try to demonstrate that until 1900, people routinely and overtly differentiated logical species which do have definitions from natural species which have descriptions and diagnostic criteria.

Classical species

Ambiguities about eidos/species and genos/genus

The role of generation of kindsGenesis 1AristotleEpicureanismMedieval (Frederick II)

Distinction between logical species, and natural species not around until Ray.

But distinction o!en made between “natural species” and “formal” species in logic.

Use of terms indi"erently depending on what the topic was.

AristotleCopulation takes place naturally between animals of the same kind [homogenesin]. However, those also unite whose nature is near akin and whose form [eidei] is not very different, if their size is much the same and if the periods of gestation are equal. In other animals such cases are rare, but they occur with dogs and foxes and wolves and jackals; the Indian dogs also spring from the union of a dog with some wild dog-like animal. A similar thing has been seen to take place in those birds that are salacious, as partridges and hens. Among birds of prey hawks of different form [eidei] are thought to unite, and the same applies to some other birds. … And the proverb about Libya, that Libya is always producing something new, is said to have originated from animals of different species [homophulē allēlois] uniting with one another in that country, for it is said that because of the want of water all meet at the few places where springs are to be found, and that even different kinds unite [homogenē] in consequence.

Of the animals that arise from such union all except mules are found to copulate again with each other and to be able to produce young of both sexes, but mules alone are sterile, for they do not generate by union with one another or with other animals. The problem why any individual, whether male or female, is sterile is a general one, for some men and women are sterile, and so are other animals in their several kinds, as horses and sheep. But this kind, of mules, is universally so. The causes of sterility in other animals are several.

[Generation of Animals II.8 746a29–746b22]

Aristotle hardly ever speaks of anything we would now call species of organisms. He uses the terms gene (genera) and eide (species), because as logical concepts it depends very much on what is being discussed. If it is something differentiated out of a larger class of things, like organs, he will speak of the “eidos” of the eye. If it is a class encompassing several subkinds, then he will use the term “genos” or variants. His student Theophrastus, in the seminal work on botany, is less careful, and will indifferently use them even in the same paragraph, perhaps for stylistic reasons. Sometimes Aristotle, as in this passage, will use the term “eidos” simply to mean form.

Of note here is that this passage ties kinds of organisms to their shared generative powers, via copulation. He is not universal about this because he thinks a good many animals spontaneously generate, but when they propagate normally, generative propensities are crucial to their kindness.

Note that Aristotle is not, here, a species fixist. He allows in a widely quoted passage from Pliny to Buffon that new species can form via hybridisation. [Libya is Africa, apart from Egypt]

Epicurus/LucretiusIf things could be created out of nothing, any kind of things could be produced from any source. In the first place, men could spring from the sea, squamous fish from the ground, and birds could be hatched from the sky; cattle and other farm animals, and every kind of wild beast, would bear young of unpredictable species, and would make their home in cultivated and barren parts without discrimination. Moreover, the same fruits would not invariably grow on the same trees, but would change: any tree could bear any fruit. Seeing that there would be no elements with the capacity to generate each kind of thing, how could creatures constantly have a fixed mother? But, as it is, because all are formed from fixed seeds, each is born and issues out into the shores of light only from a source where the right ultimate particles exist. And this explains why all things cannot be produced from all things: any given thing possesses a distinct creative capacity. [On the Nature of Things Book I. 155-191]

The atomists also had a generative conception of species. This passage from Lucretius is much later than Aristotle but most commentators think that he is faithfully reporting Epicurus’ views shortly after or even contemporaneous with Aristotle. Note that Epicurus, however, is denying spontaneous generation. This is the first clear statement of the generative conception.

MedievalRarely interested in natural species except for theological homilies

Exceptions:HerbalsAnimal Breeding Tracts

Frederick II (c1200) – keen falconer (De Arte Venandi Cum Avibus)

Criticises Aristotle for credulityBirds are same species if they will interbreed

Frederick on speciesInter alia, we discovered by hard-won experience that the deductions of Aristotle, whom we followed when they appealed to our reason, were not entirely to be relied upon, more particularly in his descriptions of the characters of certain birds.

There is another reason why we do not follow implicitly the Prince of Philosophers: he was ignorant of the practice of falconry – an art which to us has ever been a pleasing occupation, and with the details of which we are well acquainted. In his work “Liber Animalium” we find many quotations from other authors whose statements he did not verify and who, in their turn, were not speaking from experience. Entire conviction of the truth never follows mere hearsay.

...

[It] must be held, then, that for each species, and each individual of the species, Nature has provided and made, of convenient, suitable, material, organs adapted to individual requirements. By means of these organs the individual has perfected the functions needful for himself. It follows, also, that each individual, in accordance with the particular form of his organs and the characteristics inherent in them, seeks to perform by means of each organ whatever task is most suitable to the form of that organ.

Initial uses of species among early naturalistsAndreas Cesalpino, 16thC That according to the law of nature like always produces like and that which is of the same species with itself. [Quaestionum peripateticarum, libri V, ch 13]

We seek similarities and dissimilarities of form, in which the essence (‘substantia’) of plants consists, but not of things which are merely accidents of them (‘quae accidunt ipsis’). [ch 14]

Since science consists in grouping together of like and the distinction of unlike things, and since this amounts to the division into genera and species, that is, into classes based on characters (differentiae) which describe the fundamental nature of the things classified, I have tried to do this in my general history of plants, … [De plantis]

What have we skipped over in the last 400 years? Universal language project, from Bacon to Wilkins, but not much natural history. The Reformation got in the way of a lot of natural history, and science tended to focus on other matters such as medicine and anatomy.

Here it is clear that Cesalpino did think species had a kind of logical essence, but then, the idea of a natural species was not yet in play. Over the next century, the term species began to be widely used, first by Bauhin and Fuchs, and eventually by Ray.

Robert Hooke

But to refer this Discourse of Animals to their proper places, I shall add, that though one should suppose, or it should be prov’d by Observations; that several of these kinds of Plants are accidentally produc’d by a casual putrifaction, I see not any great reason to question, but that, notwithstanding its own production was as ‘twere casual, yet it may germinate and produce seed, and by it propagate its own, that is, a new Species. [Micrographica 1665]

While discussing the spontaneous generation of organisms, still believed in at this time, Hooke makes some passing comments that indicate the generative conception was still in play.

John Ray’s 1686 definition

In order that an inventory of plants may be begun and a classification of them correctly established, we must try to discover criteria of some sort for distinguishing what are called “species”. After long and considerable investigation, no surer criterion for determining species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed. Thus, no matter what variations occur in the individuals or the species, if they spring from the seed of one and the same plant, they are accidental variations and not such as to distinguish a species … Animals likewise that differ specifically preserve their distinct species permanently; one species never springs from the seed of another nor vice versa. [Historia plantarum generalis. The Latin of the definition is Nulla certior occurit quam distincta propagations ex semine.]… the number of species being in nature certain and determinate, as is generally acknowledged by philosophers, and might be proved also by divine authority, God having finished his works of creation, that is, consummated the number of species in six days. [Letter]

Linnaeus’ lack of essentialism

Never defined “species” – seemed to rely on Ray

However, some hints:Species are most constant, since their generation is a true continuation. [Species constantissimae sunt, cum earum generatio est vera continuatio. Systema naturae, 1735]

There are as many varieties as there are different plants, produced from the seed of the same species. [Varietates tot sunt, quot differentes plantae ex ejusdem speciei semine sunt productae. Philosophia Botanica 1751]

Maupertuis: the man who invented evolutionCould we not explain in this manner [of fortuitous changes] how the multiplication of the most dissimilar species could have sprung from just two individuals? They would owe their origin to some fortuitous productions in which the elementary parts [of heredity] deviated from the order maintained in the parents. Each degree of error would have created a new species, and as a result of repeated deviations the infinite diversity of animals that we see today would have come about. [Systèm de la Nature 2:164, 1743]

Pierre-Louis Moreau de Maupertuis (1678-1759) was an interesting man. He devised what we now know as the principle of least action, and showed that the earth was flattened. Some other things he did, however, changed biology forever.

In 1735, the first edition of Linnaeus' Systema Naturae was published. Linneaus put out at least 13 editions of this in his lifetime, and the famous 10th edition was adopted in the 19th century as the "gold standard" - if Linnaeus named a species, that was its name thereafter, and if not, then the first person to name it after the 10th edition, published in 1758, got the credit.

In the course of the work, and other books such as the Fundamenta Botanica, Linnaeus defined species as

There are as many species as the Infinite Being produced diverse forms in the beginning. [Species tot sunt diversae quot diversas formas ab initio creavit infinitum Ens, Fundamenta botanica No. 157, 1736]He repeated similar statements in his work elsewhere. This, of course, is a definition of what we might call stasis rather than of "species". Linnaeus, following John Ray, held that species never changed from how they were created.

Typically, we think this was overturned by Darwin, or, if we have read Darwin's own "Historical Sketch", added to the third edition of the Origin, we might think that evolution was invented by Lamarck. But in fact the first view of evolution in a scientific context was devised by Maupertuis, in the context of the Generation Debates that preceded the rise of genetics. Maupertuis noted that polydactyly, in the form of an extra finger on each hand, was passed on from generation to generation in a particular family in a 3:1 ratio, and each parent equally contributed. This, mark you, was 120 years before Mendel. In a text published finally as Venus physique (the physical Venus) in 1743, he speculated

Could we not explain in this manner [of fortuitous changes] how the multiplication of the most dissimilar species could have sprung from just two individuals? They would owe their origin to some fortuitous productions in which the elementary parts [of heredity] deviated from the order maintained in the parents. Each degree of error would have created a new species, and as a result of repeated deviations the infinite diversity of animals that we see today would have come about. [Systèm de la Nature 2:164, quoted in Terrell 2002:338]We should not make too much of this - Maupertuis was not really aware of the need for a population of individuals with genetic variance, but it is clear that he allowed there to be two processes - variation in heritable traits that arose by lucky chance, which we would call an advantageous mutation, and diversification of species from common ancestors. Unlike Lamarck, who thought each species arose individually from nonliving matter, and subsequently changed in ways that were more or less predetermined, Maupertuis has species arising by the inheritance of mutations, and diversifying, in a manner very similar to Darwin. He lacks a theory of selection, but in some ways Maupertuis should be called the Last Common Ancestor of all evolutionists.

One point that is important to note here is that almost as soon as species fixity became the widespread opinion (with Linnaeus - although Ray had put it out there earlier, it wasn't until Linnaeus became popular, mostly among botanists at first, that species fixity became the standard view, contrary to many popular histories of biology), evolutionism was offered as an alternative. There's a good reason for this. Prior to Ray, nobody thought much about whether species were fixed or not. Aristotle held they could be formed by crossbreeding, and that there were deviations from the "proper" mode of a species. Right through the middle ages and early renaissance, there was a continuing view that species were wobbly sorts of things, and in the 18th century it became a fashion to gather species deviants - monsters and curiosities, as they were called - in cabinets to show to friends. It is simply false that species were always held to be fixed. But evolution, in the sense of a historical series of changes of species one into another, needed fixism as a contrast before it could be conceived, and it took all of 8 years after the Systema

Buffon – non-hybridising animals (mules)

We should regard two animals as belong to the same species if, by means of copulation, they can perpetuate themselves and the likeness of the species; and we should regard them as belonging to different species if they are incapable of producing progeny by the same means. Thus the fox will be known to be a different species from the dog if it proves to be a fact that from the mating of a male and female of these two kinds of animals no offspring is born; and even if there should result a hybrid offspring, a sort of mule, this would suffice to prove that fox and dog are not of the same species – inasmuch as this mule would be sterile (ne produirait rien). For we have assumed that, in order that a species might be constituted, there was necessary a continuous, perpetual and unvarying reproduction (une production continue, perpétuelle, invariable) – similar, in a word, to that of other animals. [Histoire naturelle Vol. 2 (1749), 10]

John Hunter 1787

The true distinction between different species of animals must ultimately, as appears to me, be gathered from their incapacity of propagating with each other an offspring capable again of continuing itself by frequent propagations: thus the Horse and Ass beget a Mule capable of copulation, but incapable of begetting or producing offspring.

Jussieu

... species, [a term] wrongly used in the past, now more correctly defined as the perennial succession of like individuals, successively reborn by continued generation. [Genera plantarum secundum ordines naturalis disposita (1789)

...in one species are to be assembled all vegetative beings or individuals that are alike in the highest degree in all their parts, and that are always similar [“conformia”] over a continued series of generations...

Lamarck – fixed essence

Species: in botany as in zoology, a species is necessarily constituted of the aggregation of similar individuals which perpetuate themselves, the same, by reproduction. I understand similarity in the essential qualities of the species, because the individuals which constitute it offer frequently accidental differences which give rise to varieties and sometimes sexual differences, which belong however to the same species, as the male and female hemp, in which all the individuals constitute the cultivated hemp. Thus, without the constant reproduction of similar individuals, there could not exist a true species.

[Encyclopedie Methodique, Vol. 2, 1786]

Lamarck – no such thing as species

It is not a futile purpose to decide definitely what we mean by the so-called species among living bodies, and to enquire if it is true that species are of absolutely constancy, as old as nature, and have all existed from the beginning just as we see them to-day; or if as a result of changes in their environment, albeit extremely slow, they have not in the course of time changed their characters and shape. …Let us first see what is meant by the name of species.Any collection of like individuals which were produced by others similar to themselves is called a species.This definition is exact: for every individual possessing life always resembles very closely those from which it sprang; but to this definition is added the allegation that the individuals composing a species never vary in their specific characters, and consequently that species have an absolute constancy in nature.It is just this allegation that I propose to attack, since clear proofs drawn from observation show that it is ill-founded.

[Zoological philosophy 1809]

Lamarck – ... just parents and children

Thus, among living bodies, nature, as I have already said, definitely contains nothing but individuals which succeed one another by reproduction and spring from one another; but the species among them have only a relative constancy and are only invariable temporarily. ...

Nevertheless, to facilitate the study and knowledge of so many different bodies it is useful to give the name species to any collection of like individuals perpetuated by reproduction without change, so long as their environment does not alter enough to cause variations in their habits, character and shape.

[Zoological philosophy 1809]

Heredity

Lewes 1856 review online http://scienceblogs.com/evolvingthoughts/2007/06/lewes_on_heredity_in_1856.php

Shift from Generation to Heredity

Shift from similarity to fertility

Hybridism from Interspecies to Within-Species

Shift from Terata to Variance

ConclusionsThe Generative Conception ruled from Aristotle to Just Before Darwin

Aristotle was almost always not the source for the use of the term after about 1700

“Biological” (Reproductive Isolation) Conceptions occur from 1740 or so, dealing with the existence of mules

Pre-Darwinians were good observers