Darwin and Logic

In my ongoing campaign to catch up on recent literature, I have managed to acquire a copy of An Introduction to Logic by H. W. B. Joseph, Oxford University Press, 2nd edition (1916) - I had a very poor and nasty reprint from an Indian printer. Never again...

In browsing through this recent modern work (historians of ideas are to history as geologists are to biology), which figured prominently in my thesis, but I hadn't read through entire, I found this:

... how long may an hypothesis be destined to remain an hypothesis without prejudice to its genuinely scientific character? The ultimate destruction of life on earth is assumed by science; for human minds, an hypothesis which is not proved or disproved by that date will always remain an hypothesis. We cannot suppose that its scientific character, when it is made, is to be estimated by the prospect of its truth being definitely ascertained a few years, or even a few myriads of years, earlier or later. [Here comes the kicker - JSW] Darwin, in the Origin of Species, [Joseph's note: Origin of Species, c. xiv, 6th ed. p.396. The italics are mine.] writes as follows" ' As the embryo often shows more or less plainly the structure of the less modified and ancient progenitor of the group, we can see why ancient and extinct forms so often resemble in their adult state the embryos of existing species of the same class. Agassiz believes this to be a universal law of nature; and we may hope hereafter to see the law proved true. It can, however, be proved true only in those cases in which the ancient state of the progenitor of the group has not been wholly obliterated, either by successive variations having supervened at a very early period of growth, or by some variations having been inherited at an earlier stage than that at which they first appeared. It should also be borne in mind, that the law may be true, but yet, owing to the geological record not extending far enough back in time, may remain for a long time, or for ever, incapable of demonstration'. [end Darwin quote] But that the rule in question is an universal law is a scientific hypothesis.

[pp465-66.]

This is an amazing passage for a number of layered reasons.

First, a logician and philosopher of science (the two were effectively identical at that time, and had been since Whewell, Mill and Jevons in the previous century) considered in that period (the so-called "eclipse of Darwinism" period) that Darwin had proposed a scientific law of evolution, following Agassiz (and von Baer, although he is not cited in this instance). Joseph in no wise considers evolution to be unscientific here.

Second, Darwin's own prose - so clear and spare, and yet direct. He notes that the ancestral states might be obtainable by observing them in embryos, but mentions the obvious - subsequent history can obscure the past. Or, as I like to think of it, information is lost over time. This is an important point, one not properly appreciated by Haeckel in his ontogenetic law, for he hoped or assumed that ancestral information was always retained, mostly.

Third, the fact that Darwin understood the historical logic of evolution, still better than a great many evolutionary biologists since.

Fourth, that a logician was able to see this, and appreciate it.

Whether a claim is scientific or not has been a bone of contention since philosophy and science first butted heads (around the time of - you guessed! - Aristotle). We often hear that hypotheses must be tested and cannot be called scientific if they are not able to be tested - when? Why now, of course. This impatience in Popperian philosophy is one of the reasons why Kuhn developed his own view of science as progressing happily in Ordinary Science even though there were anomalies and problems. Joseph points up something we sometimes forget - a hypothesis can be scientific even if we cannot prove or disprove it.

And what does he use as his paradigm case (the proper use of "paradigm", he said grumpily)? Charles Darwin, and his theory of evolution. Very telling...