Saturday, 29 April 2017

Comparing Matthew's and Darwin's theories

The following analyses and compares the evolutionary schemes of Patrick Matthew and Charles Darwin.

1. Matthew’s propositions
In his book On Naval Timber and Arboriculture, Patrick Matthew explicitly excluded the wider range of circumstances under cultivation as the cause of increased differences in varieties and attributed it instead to man’s interference with natural selection:
Man’s interference, by preventing this natural process of selection among plants, independent of the wider range of circumstances to which he introduces them, has increased the difference in varieties particularly in the more domesticated kinds.1 (Matthew 1831, 308)
Furthermore, he regarded adaptation to be relative in comparison to competitors as illustrated by examples that ecologists would today call cases of competitive exclusion:
The natural soil and climate of a tree, is often very far from being the soil and climate most suited to its growth, and is only the situation where it has greater power of occupancy, than any other plant whose germ is present. The pines do not cover the pine barrens of America, because they prefer such soil, or grow most luxuriant in such soil; they would thrive much better, that is, grow faster, in the natural allotment of the oak and the walnut, and also mature to a better wood in this deeper richer soil. But the oak and the walnut banish them to inferior soil from greater power of occupancy in good soil, as the pines, in their turn, banish other plants from inferior sands —some to still more sterile location, by the same means of greater powers of occupancy in these sands.”2 (Matthew 1831, 302f, his emphases)
While the oak did better than the pine on rich soils, it fared worse on poor soils. They excluded each other on the respective soils. Without competition, the pine would also do better on rich soils. While evolutionists could now call this idea relative fitness or adaptedness and ecologists could call it reciprocal competitive exclusion (pines from rich soils oaks from poor soils), Matthew called it the power of occupancy.
    However, Matthew did not state this observation of relative fitness, in order to develop an evolutionary argument. On the contrary, the problem at hand was the practical question where to plant different tree species in order to get the best timber. In particular, Matthew (1831, 302f) used his observation to refute Steuart’s claim that trees should always be planted in the soils and climates that resemble their natural habitat. Instead, he maintained that pines would yield better timber if planted in soils that were richer than their natural provenience because they were only excluded from these soils by competitors.
    And further down he used the same logic of this argument, in order to confirm Cruickshank’s claim that the oak could grow throughout Scotland although it does not tend to do so naturally:
The highest latitude to which a tree, or any other kind of plant, reproducing by seed, naturally extends, depending on the ripening of the seed, and also on the power of occupancy, is however different from that where it will grow, when ripe seeds are produced from the coldest place where they ripen, and all the competitors removed; and under the system of shelter belts, hardy pine nurses, and seeds from the nearest place where they ripen, we have no doubt that oaks may be extended to a colder situation than Nature herself would have placed them. (Matthew 1831, 356f)
Again, the problem at hand was not evolutionary, but the practical question whether the area for growing the valuable oak timber could be expanded by a system of getting seeds from the coldest places, where they still ripen, putting them into nursery belts sheltered by hardy pines and removing all competitors from the immediate vicinity.3
    Finally, he explicated his evolutionary ideas in an addendum to the appendix and integrated his concept of relative fitness (power of occupancy) into it as follows:
1. Species are fixed for long periods of time:
A particular conformity, each after its own kind, when in a state of nature, termed species, no doubt exists to a considerable degree. This conformity [of species] has existed during the last forty centuries. (Matthew 1831, 381)
2. Geologists discover like conformities of fossil species within each epoch, but also almost complete difference between the fossil species of one epoch from those of all others (Matthew 1831, 381).
3. This discontinuity (punctuation in the fossil record) is initiated by catastrophes.
The destructive liquid currents […] destroying nearly all living things, must have reduced existence so much, that an unoccupied field would be formed for new diverging ramifications of life […], these remnants, in the course of time, moulding and accommodating their being anew to the change of circumstances, and to every possible means of subsistence, and the millions of ages of regularity which appear to have followed between the epochs, probably after this accommodation was completed, affording fossil deposits of regular specific character. (Matthew 1831, 382f)
4. Pondering the question whether the transformation of species after such a catastrophe was due to repeated new creation, admixture of species, or adaptation (“gradual circumstance-suited modification”), Matthew (1831, 384) opts for the latter.
5. He then, partly, attributes this adaptation to natural selection in a paragraph in which the power of occupancy re-occurs:
The self-regulating adaptive disposition of organized life may, in part, be traced to the extreme fecundity of Nature, who, as before stated, has, in all the varieties of her offspring, a prolific power much beyond (in many cases a thousandfold) what is necessary to fill up the vacancies caused by senile decay. As the field of existence is limited and pre-occupied, it is only the hardier, more robust, better suited to circumstance individuals, who are able to struggle forward to maturity, these inhabiting only the situations to which they have superior adaptation and greater power of occupancy than any other kind; the weaker, less circumstance-suited, being prematurely destroyed. This principle is in constant action, […] in such immense waste of primary and youthful life, those only come forward to maturity from the strict ordeal by which Nature tests their adaptation to her standard of perfection and fitness to continue their kind by reproduction. (Matthew 1831, 384f, my highlighting)
6. Finally, he states how this explains both the conformity (fixity) of species in the periods of stasis as well as their transformation after catastrophic changes:
From the unremitting operation of this law […], a considerable uniformity of figure, colour, and character, is induced, constituting species; the breed gradually acquiring the very best possible [not perfect] adaptation of these to its condition which it is susceptible of, and when alterations of circumstance occur, thus changing in character to suit these as far as its nature is susceptible of change. (Matthew 1831, 385)
The remainder of this addendum is made up of considerations of additional causes of adaptation (hence he traced adaptation only “in part” to natural selection) as well as the anomaly of the human species that either modifies other species to its needs or exterminates them.

2. Darwin’s theory development
Eiseley (1959) interpreted Darwin’s statements from 1844 and 1868 as if they were statements of one and the same theory. Since then, Darwin studies have traced Darwin’s long theory development in minute detail (e.g., Ruse 1975; Browne 1980; Kohn 1980; 1986; 2009; Schweber 1980; Beddall 1988; Mayr 1992; Richardson 1981; Ospovat 1995; Hector and Hooper 2002; Costa 2009; Mannouris 2011; Pearce 2010; Richards 2012). Consequently, Darwin’s earlier statements cannot be taken to be informed by the same theory as his later ones. Before getting into a detailed comparison of Darwin with Matthew, let me briefly sketch Darwin’s intellectual development in a conveniently simplified way. Between his return from the Beagle voyage and 1844, Darwin developed what will be referred to as his early theory of species transformation through natural selection. Between that time and 1856, he was obsessively occupied with taxonomic work concerning small-scale studies of barnacle variation (LIT) as well as large-scale patterns in botanical systematics (Browne 1980). Thereafter, he began to write down his mature theory, posthumously published as Natural Selection (Stauffer 1975), but this was famously interrupted by a letter from from Alfred Russel Wallace precipitating the events that lead to the publication of the Origin of Species as an abstract of the big Natural Selection book he had planned.

2.1 Darwin’s early theory
Despite embracing the idea of species transformation by 1837, he continued to work by theories that agreed with doctrines of natural theology up to the mid-1850s. For example, Darwin (1909[1844]) thought that species hardly varied under natural conditions, because intermarriage would swamp individual variants. He thought that large scale changes in conditions needed to push organisms out of their natural state first. This would affect their reproductive system to increase fortuitous variation in the offspring. Only after this boost of undirected variation could selection adapt the species to the new conditions. Under normal conditions, natural selection was stabilising (keeping species fixed) as generally believed to be true in doctrines of natural theology. Natural selection could only transform species under exceptional conditions.

2.2 Darwin’s later theory
In the mid-1850s Darwin removed the special conditions of existence from the center stage of his theory and allowed that even slight individual differences could be accumulated by natural selection without being swamped. The keystone in this development was his principle of divergence.4 This did not simply explain the long known pattern of diverging ramifications as a contingent result of variation and selection, speciation and extinction, but took divergence as adaptive in itself.5 The sources motivating Darwin’s search for this principle have been traced to studies on embryology, morphology, taxonomy and first ecological experiments by von Baer, Owen, Milne-Edwards and Sinclair respectively (Browne 1980; Kohn 1981; 1986; 2009; Schweber 1980; Beddall 1988; Mayr 1992; Ospovat 1995, chap. 5-8; Hector and Hooper 2002; Pearce 2010; Richards 2012).
    Darwin tried to explain a large-scale pattern of taxonomy that the species within larger genera were also more divergent morphologically than the species in smaller genera. He had invested a lot of research into developing a statistical measure for that pattern and the principle of divergence was his explanation of it (Browne 1980). Starting from an analogy with economic specialisation, Darwin apparently arrived at the conclusion that specialisation is also advantageous for species (Tammone 1995) and construed his principle of divergence as an explanation for the taxonomic pattern from it.
  Darwin (1859, 114, 116, 118, 121), took species to be imperfectly adapted and divergent forms to be improved (better specialised) and therefore to almost necessarily exterminate the intermediate forms, which were usually the own parental forms.
As each species tends by its geometrical ratio of reproduction to increase inordinately in number; and as the modified descendants of each species will be enabled to increase by so much the more as they become more diversified in habits and structure, so as to be enabled to seize on many and widely different places in the economy of nature, there will be a constant tendency in natural selection to preserve the most divergent offspring of any one species. Hence during a long-continued course of modification, the slight differences, characteristic of varieties of the same species, tend to be augmented into the greater differences characteristic of species of the same genus. New and improved varieties will inevitably supplant and exterminate the older, less improved and intermediate varieties; and thus species are rendered to a large extent defined and distinct objects. (Darwin 1859, 470)
The pattern of diverging ramifications was no longer contingent but a necessary result of adaptative change, first, and competitive extinction of intermediate forms thereafter. This idea is no longer valid (Mayr 1992, 354f). Why should selection inevitable preserve the diverging (more specialised) form and exterminate the parental (more generalist) form? The point, here, is not whether Darwin’s principle of divergence is still valid today, but that its development, causal structure and consequences differs from Matthew’s ideas as follows. 
    To distinguish Darwin's early from Darwin's late theory, one could say that the drive for adaptive change was environmental in his early theory, but competitive in his later theory.

3. Theory comparison
Historians of science often claim that Darwin's early theory or theories of others from before The Origin of Species in 1859 included a conception of perfect adaptedness (e.g., Ospovat 1995; Fleming 2013). To address that claim, the meaning of perfect and relative adaptation needs to be clarified first. Perfect adaptation requires two things: (1) A perfectly adapted species will not do better elsewhere and (2) it can also not be ousted from its niche, neither by other species nor by divergent descendants of its own. Suppose a species that was perfectly adapted for one niche but its actual range beyond this spot was restricted by competitors. That would fulfill conditions 1 and 2 from above. But it cannot be Matthew's conception, because such a species would not do better elsewhere.
    Let's stick with Matthew’s example of pines and oaks. If, for example, pines were perfectly adapted for poor soils and cold climate, they would do best there. Rich soils and warmer climate would have adverse physiological effects (similar to over-manuring or desiccation). Pines could still occur on rich soils in the absence of superior competitors, but they would not do as good there as on poor soils. Matthew, however, thins that pines would really do better on rich soils, if only the competitors would not exclude them. Matthew's concept of imperfect adaptation breaks condition 1 for perfection, but Darwin later theory breaks both condition 1 and 2. 
    This explains why Darwin, in his early theory, needed environmental change to alter the conditions to which a species was perfectly adapted and thus induce it to vary markedly, as if under domestication. First the environmental factors change and render a species ill adapted, then it varies markedly, then natural selection works to transform it. Geographic isolation is needed in this early theory, in order to get more than one species.
   The relative adaptation of pines and oaks in Matthew’s scheme also explains why he did not merely need environmental change but catastrophes. The catastrophe needs to exterminate the competitors and leave an unoccupied field of existence into which the pines could then spread and thereafter adapt to the new conditions which they meet there. That is, Matthew's scheme would even work if, no environmental change occurred, but the competitors were nevertheless removed somehow. That’s why he advised to remove the competitors if one wanted to grow oaks in Scotland or pines on rich soil. Conversely, if the soil of the pine habitats became rich and the climate mild, somehow, but that of the oaks would stay as it was, the latter would simply exterminate the former. Hence, catastrophes.
   Imagine a miraculous catastrophe that would exterminate the majority of all species, but leave the environmental conditions on earth just as they were. Such a catastrophe would have the same effect in Matthew's scheme as one that altered the environmental conditions along with exterminating competitors. With perfect adaptation, however, the pines would keep sitting in their niche of poor soils and cold climates and their spread to adjacent habitats would be an extremely slow process. The variant occurring could move only tiny bits beyond the conditions perfect for their ancestors. It would not possibly yield the ultra-rapid adaptive change that Matthew needs in his scheme.6
   In comparison, Matthew's scheme is one of stasis punctuated by catastrophes; in the periods of stasis natural selection keeps the species to their niches. This agrees with the doctrine of natural theology in that natural selection has a species fixing effect during stasis. It disagrees with natural theology in that species are not perfectly adapted to their niche, but only kept there by competitors. Therefore, catastrophes have a species transforming effect by removing competitors. Matthew does not need repeated creation, because the remnant species will naturally spread into the empty fields of existence after a catastrophe. The same natural selection that kept the species fixed now transforms them.
    In Darwin's mature theory, after the principle of divergence, the environmental conditions included other species, but the fiercest competitor of a parental species was the divergent daughter species. That is, the oak was not exterminated by a catastrophe and then the pine moved in, but the parental oak was exterminated by divergent daughter species (other oaks) that were more specialised and therefore better adapted.
    In Matthew's scheme relative adaptedness means that the pine could do better on rich soils and would spread there, if the competitors (hardwood) were removed. In Darwin's later scheme relative adaptedness means that a pine species which could do better on rich soils could also be better adapted for poor soils than it actually is. Therefore divergent descendant species (that are more specialised for poor soils) will oust the parental species. That is how the principle of divergence is the inverse of Matthew's idea of relative power of occupancy. Where Darwin saw sharp wedges packed close together and driven inwards by incessant blows, Matthew saw pointed arrows lashing outwards by incessant throws.
   As the conception of perfect and relative adaptedness is useless for describing Matthew's scheme of evolutionary change, it should be replaced by a conception that distinguishes between an environmental and a competitive drive for adaptive change. We then see that Matthew's theory conceived competition as a stabilising factor and catastrophes as an environmental drive for change by clearing the field from competitors. In Darwin's early conception the environmental change does not drive evolutionary change by removing competitors, but by removing the species from its zone of comfort. 
   In Darwin's late theory, however, competition has become the drive for evolution and environmental change can increase this drive. But competition is never a hindrance to adaptive change in any of Darwin's theories as it is in Matthew's.
    For redundancy, Matthew's concept of relative adaptedness means that the pine is not the species that is best adapted to rich soils and therefore ousted from them, and the oak is not the species best adapted to poor soils and therefore ousted from them. However, although both are only better adapted to their natural place than the competitors—not perfectly adapted—Matthew did not use that, in order to develop an intrinsic evolutionary drive from it (like the principle of divergence). Instead he took on board the external driver of catastrophes.
    For Darwin, the pine is better adapted to poor soils than the oak, okay, but it could also be still better adapted to its natural habitation on poor soils. And Darwin uses that for developing an intrinsic evolutionary drive that needs no recourse to external drives. He used to need the external drive of changed conditions in his early theory, in order to push a species from its comfort zone. But his later theory, while it can accommodate such external factors of evolution, has in in-build drive for adaptive change (the principle of divergence).

4. Conclusion
In conclusion, Matthew’s theory of evolution is a chimera pairing the old doctrine that natural selection (usually) keeps the species fixed with the catastrophism that allowed for rapid transformation and radiation of species by natural selection after a catastrophe. Darwin’s principle of divergence, however, was his final break away from the doctrine that natural selection kept species fixed.
    The principle of divergence differs from Matthew’s ideas in its development (from Darwin’s own studies of systematics and an analogy with economics), its causal structure and its consequences. This constitutes a negative paternity test for Matthew. It exculpates Darwin from claims of plagiarising Matthew for the time after he shifted from his early (1844) to his mature theory (1856-58). His early theory, without the principle of divergence, was equally different from Matthew’s ideas:
Darwin: environmental change renders a species ill adapted → this leads to increased variation → this allows species transformation by natural selection;
Matthew: adaptation is always relative → competition keeps species fixed in their natural place → catastrophe removes competition → species spreads and natural selection transforms it to new conditions. 
This exculpates Darwin for the time from his return from the Beagle voyage till 1844. Hence, the time window left for this particular plagiarism claim is hardly open anymore. 

--- Notes ---
 
1 Note that “difference in varieties” does not necessarily mean individual variability.
2 Prideaux John Selby (1842, 391) cites this passage of Matthew only to refuse it: “Matthew, however, in his able treatise on naval timber seems to think that its indigenous location in such districts arises not so much from preference of soils of the nature above-mentioned, as from its having more power of occupancy in such soils than any other plant of the country; and this opinion he endeavours to support by stating that the Pinus sylvestris, planted in a good or rich soil, attains larger dimensions and its best timber properties, and that it is only driven from this superior soil by the greater power of occupancy, and that it is only driven from this superior soil by the greater power of occupancy possessed by the oak and other deciduous trees, an opinion in which we cannot altogether acquiesce, as we see no reason why the fir, if it grows with such additional vigour in a richer soil, as Mr. Matthew asserts, should, at the same time, be unable to maintain a contest with the oak or other tree.” Apparently, Selby did not comprehend the dynamics of competition and simply assumed that equal size at maturity of pine and oak meant equal competitive powers.
3 Again, he reiterated this logic of relative fitness in his book Emigration Fields Matthew (1839, 38): “The soil of Upper Canada is in many places of fair quality, and generally superior to that of the eastern provinces. The timber consists mostly of large-leafed deciduous trees, while that of the eastern provinces is chiefly pine. This distribution is partly due to soil as well as climate, and has lead to the belief that pines prefer inferior soils. This, however, is not the case. Hard-wood trees have only greater power of occupancy in warmer climates and richer soils and pines in the cold and inferior, especially in the more siliceous.” (see also p. 57)
4 Davies (2013, 727) suggested that Wallace (1856, 214)could have inspired Darwin’s principle of divergence: “It is probable that in very few cases is there a direct affinity between two groups, each being more or less distantly related to some common extinct group, so that we should represent their connexion more accurately by making our central line a blank, for the extinct portion of the group, and placing our families right and left, at different distances from it.”
5 Though anachronistic, the modern distinction between stabilising, directional, and disruptive selection can help understand the principle of divergence. Where, beforehand, the usual circumstances of a species rendered natural selection stabilising, or absent according to Darwin’s early theory, and changed conditions of life were required to render it directional (transforming), disruptive selection for divergence could now also occur under the usual conditions of existence. Transformation, speciation, and extinction were no longer conditional upon large-scale changes of physical circumstances.
6 Matthew (1831) believed that “millions of ages” (p. 383) of stasis, the last one lasting “forty centuries” (p. 381) had been punctuated by an equal number of catastrophes followed by short periods of adaptation and diversification. To cut him some slack, let the average period of stasis be 3000 rather than 4000 years. This will amount to 3 billion years of stasis. Life on earth exists for 3.9 billion years, minus the stasis leaves 900 million years for adaptation. Slotting them in after the catastrophes and before the periods of stasis leaves 900 years, on average, for each period of evolutionary change. And in that time the new fauna and flora had to re-evolve from catastrophes “destroying nearly all living things” (p. 382f). This extremely compressive limitation shows that Matthew’s scheme lacked time for evolutionary change.

--- References ---
  
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