07-14-11, 07:33 AM #1
A Scholastic Approach to the Species Problem
Questions from a previous discussion about the "Species Problem" are as follows:
How would you answer the following questions?
1) Does the term "species" refer to either individuals or classes?
2) Is "species" real or or not? In other words, does "species" have an objective existence outside our intellectual abstractions or is it just a useful delusion?
3) How do you define species so that it adequately catalogue all the different life-forms?
A Scholastic approach is as follows:
The thesis whereby "species" is a natural kind and individuated by essences is known as essentialism. Natural kinds are universals not individuals on this view.
The Scholastic approach (and others) differentiates between the five predicables; Species, Genus, Differentia, Property and Accident (Coffey P, The Science of Logic). The predicables are relations to individual things or subjects or substances.
The "species" predicable is related to an individual substance in a manner that describes whole specific nature of the individuals in a class.
The "genus" predicable is related to an individual substance in a manner that describes something about the substance that is in common with other substances.
The "differentia" predicable is related to an individual substance in a manner that describes something about substance that distinguishes it from other substances in the same genus.
The "propria" (or property) predicable is related to an individual substance in a manner that describes something about the substance that necessarily follows from its essence or nature.
The "accidens" predicable (or accident) is related to an individual substance in a manner that describes an attribute about the substance that does not necessarily follow from its essence or nature.
The "definition" of a substance is something that describes the nature of the thing that is not only clear but distinct. The "definition" of a substance is described by the "species" predicable and not necessarily the "infima species" but instead the "essential species" or "natural species". The genus above the "essential species" is called the "proximate genus".
The "accidens" predicable is divided between separable and inseparable accidents. An inseparable accident is "some quality which is found to belong invariably as a matter of fact to all the members of a class" (Coffey P, The Science of Logic Vol1 , p87). A separable accident is a quality that is not necessarily present in all the members of a class.
The Porphyrian tree
One way of demonstrating the relationships between the predicables is by drawing up a Porphyrian tree (Figure 1).
Figure 1: An example of a Porphyrian Tree
Let's take the example of a scalene triangle and apply the various predicables to it (Figure 2).
Figure 2: A Porphyrian Tree for a Scalene Triangle
Summum genus = Mathematical figure
Proximate genus = Straight lined 2D Mathematical figure
propria = Three sides
Essential species = Triangle (Nature or essence = triangularity)
Defiinition = Three sided, straight lined 2D Mathematical figure
Differentia accidens inseparable = all sides are different.
Infima species = Scalene triangle
The answers to the above questions (first two) from a Scholastic view are thus as follows:
1) Species (both essential and infima) refer to a group or population of individuals. I.e it is a class.
2) Essential species are natural kinds and thus a universal. Moderate realism is applied to universals as described here.
The question now is how to apply the concepts to properly catalogue all the different life-forms in reality. The Scholastic differentiation between contingent and necessary being is useful as well as the the differentiation between substance and accident (Figure 3).
Figure 3: Being - Necessary and Contingent
Substance and accident are the summum genus for modes of contingent being. A Porphyrian tree for accidents is described here. Generating a Porphyrian tree to describe the various predicables of substances is thus the next step.
07-14-11, 07:42 AM #2
Natural kinds or Essential Species
Material or embodied or corporeal substances can be differentiated between living and non-living substances. Living substances are composites of matter and form, actuality and potentiality, essence and the act of existence (the Thomistic doctrine). On this view, (following the Aristotelian-Scholastic view) all living substances’ form is the “soul“. The kind of form a living substance has is determined by the kind of "essential species" (not infima species) a living substance is. The basic characteristic that differentiates living substances from non-living things is immanent activity and causation. Following Oderberg’s (Ref 1) definition:
1) A living substance is just a substance with the natural capacity or power for self-perfective or self-maintaining immanent activity.
2) A living substance acts for itself in order to perfect or maintain itself by producing, conserving and repairing its proper functioning.
3) A living substance is able to do 1) and 2) by means of immanent causation whereby the efficient causation begins with the substance and ends with the substance for the sake of the substance. I.e. a substance can be argued to be closed to efficient causation (Louie, 2008) (2).
Homeostasis thus is the hallmark of immanent activity and causation. All living things are capable of performing some sort of homeostatic function and such a function is characterized by 3 mechanisms:
These 3 mechanisms of homeostasis in living things are thus responsible for metabolism, repairing and the potentiality of replication. It is possible for substances to have some sort of homeostatic function without having the potential to replicate e.g. a thermometer. Thus, having at least the potential to replicate is another distinguishing feature of living things.
In a nutshell, livings are differentiated from non-living things by the fact that they are capable of immanent causation and activity, AND homeostasis (metabolism and repair) AND have the potential to replicate.
Living substances can then be differentiated between motile and non-motile living substances. Motile living substances are (according to this view) termed as "animals" and non-motile living substances are terms as "vegetals" (Figure 4). Animals can be further differentiated into conscious and non-conscious animals. Consciousness is just the ability to be self-aware and have subjective feelings. Non-conscious animals are tentatively called "critters" on this view. Conscious animals can be differentiated between intellectual and non-intellectual animals. An intellectual animal is an animal that has the capacity or power to abstract universals from particulars via reason. Such animals are termed "man" and non-intellectual (but conscious) animals are termed "beasts". Thus, there are 4 essential species or natural kinds of species which can be further differentiated by their inseparable accidents into infima species (Figure 4). The various taxonomic classes and current ways of defining "species" can be used to help to identify the inseparable accidents. For example relational (e.g. phylogenetic) and morphological analyses can be used.
Thus (on this view), there are four natural kinds (essential species) of living things derived with the aid of metaphysical-cum-philosophical analysis e.g.:
1) Non-animal (vegetal) soul.
2) Unconscious animal (critter) soul.
3) Conscious animal (beast) soul.
4) Intellectual (rational) animal (man) soul.
These are in turn differentiated into infima species with the aid of current taxonomic procedures (Figure 4).
Figure 4: Living substance Porphyrian tree
The idea behind the "animal" distinction is to differentiate between motile and non-motile living things as a property and not an inseparable accident. I suppose "animate" or "motile" can be used instead and if we stick with "animal" then it can be decoupled with the taxonomy used for infima species where inseparable accidents are used as distinctions between the infima species.
With regards to the "essential species" concept and its relation to evolutionary biology:
The four features that distinguish between the four essential species are immobility or immotility, motility or mobility, consciousness and rationality. I would argue that those four features are basic features that can be used to differentiate between any organism irrespective of their ancestral relation, morphology, physiology, biochemistry, biology etc.
Those are four properties that necessarily follow from its essence or nature or natural kind of thing it is. Say for example we where to travel to another planet and discover life (and of course this depends on whether this approaches' current definition of life is satisfied as described) we would (I would argue) still be able to distinguish between the four kinds of "essential species" irrespective of their ancestral relations, morphology, physiology, biochemistry, biology etc.
Is it capable of moving from one place to another on its own or not? If not it is a vegetal. If so, it is motile. If it moves, is it conscious, if so, is it rational etc.?
Of course the more we understand these creatures, the more we would understand their inseparable accidents. And it is here where phylogenetic analyses, physiological and morphological characteristics, biochemical characteristics etc. all can play a role in identifying infima species.
Speciation and Evolution
Speciation on this view thus occurs between the essential species. This scheme can be argued to be robust enough to incorporate other life forms on other planets (if they exist). Thus, the Scholastic approach to the species problem (a philosophical problem of biology) is a philosophical approach that incorporates the the Aristotelian concepts of substance and accident, matter and form, four causes etc. that is compatible with empirical taxonomic categories that are currently employed (e.g relational, biological, morphological etc.) as well as the findings of evolutionary biology. Evolution is just another word for change and the Scholastic approach to change has been described here.
This is of course just a brief outline of one kind of Scholastic approach towards the species problem and by no means representative and there is always room for improvement.
For the Aristotelians out there, how do you think it can be improved?
For the rest, in what way is this approach incompatible with evolutionary biology?
07-14-11, 10:13 AM #3
I think by "class" you mean to say "clade," or perhaps "taxonomic group."
A class is a specific level of taxonomy. For example:
- Domain: Eukaryota
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Primata
- Family: Hominidae
- Genus: Homo
- Species: Sapiens
Species is subordinate to class, and I'm sure that's not what you meant.
07-14-11, 10:35 AM #4
Class in the context of this discussion is just to distinguish between a universal and a particular. Individuals are particulars. A class is a universal if you want. Genus, Family, Order, Class, Phylum, etc. all are examples of universals. This approach (the Scholastic approach) takes species to be a universal (not a particular as in Ghiselin's approach) combined with moderate realism as opposed say Platonic or anti-realism.
07-14-11, 12:30 PM #5
07-14-11, 01:01 PM #6
07-14-11, 01:14 PM #7
I suppose the term "universal category" can be used to help get the point across.
07-14-11, 03:50 PM #8
The word is not philosophy's to define.
You might more usefully inquire as to how "species" is used, and defined by that use, already.
07-14-11, 04:25 PM #9
The "species problem" is a philosophical problem. How "species" is used and defined is precisely the issue. There are of course various approaches, this is one. I would argue that the most useful approach and the one that corresponds best to reality is the best way forward.
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