skip to content

Darwin Correspondence Project

From D. T. Smith   19 November 1872

Louisville Ky

Nov 19th 1872.

Mr Charles Darwin

Dear Sir;

I have mailed you three numbers of the Louisville Courier-Journal containing an abstract of a series of lectures given by myself upon the theory of the descent of man, of which you are the author and which is everywhere known by your name.1 Together with your own I have reviewed the theory of Mivart2 and others, and attempted to substitute for them a new and different theory

Owing to press of matters of local interest, the paper could not publish a full report of the lectures, and they therefore appear in a very fragmentary form, and beside contain a large number of typographical errors. However, to you this will matter little, as with a bare suggestion of any theory on this subject, you would of course, perceive at once the full bearing of it, and recognize all the facts that might rightly be ranged under it. There are a few features however which I hope it may not be trespassing upon your time for me to be a little more explicit upon.

The explanation of the closer resemblance of ancient and melanian3 skeletons to those of apes than is borne by recent ones, which is barely mentioned in the reports, rests upon the supposition, that the body and mind are twin effects of the soul, produced by it whilst working with the common force as an instrument, and that when either of these or any department of either of them receives undue force or attention from the soul, the other or the rest must suffer to that degree. It is also supposed that the power of the soul is definite and limited within a certain slightly varying degree. Now ununited sutures, and abundant cartiliaginous structures are found in children, while advanced ossification is characteristic of age.4 The one then may be taken as evidence of weaknesses of developing force, the other a strength.

Low and savage races, neglect the cultivation of mental capacity, consequently in them the soul is caused to devote its energies to the development of the parts of vegetable instead of those of animal life. The soul I conceive to be the agent in the parent, that by means of the instrumentalities already mentioned, modifies the essential atoms and forces of lower beings, that is frees them from lower impressions, and places them together rightly in the germ and directs each to it proper task

If in the parent the development of vegetable life is excessive, an excess of energy will be given to such atoms of the germ as are destined to the building up of the body, possibly resulting in the selection of an excess in that department, but more likely in devoting to that work such atoms as have for their proper office the production of the parts involved in mental capacity. Thus an excess of work being undertaken, of a kind removed as far as possible from the standard laid down for the species, that work in as far as it is unusual to the vital energies of the species will be imperfectly performed. Therefore although in an individual or germ thus produced, more than the average development of the atoms and forces of lower beings may have been accomplished, even in the direction of vegetable life, by the forces of the parent organism, yet too much having been undertaken in that direction by the parent energies, some of the essential atoms and forces, possibly diverted from their office of building up parts essential to the production of mental capacity, will not be properly modified, and will thus go on to build up in the human body, such structures as they had been building up in the bodies of lower beings. And in this way the proper correlations of growth will be interfered with.

If the effort were pushed beyond this, I take it, reproduction would fail. On the other hand if the reproductive effort should fall short of the proper standard, we should have a case of reversion from arrested development, the tendencies of the essential atoms or forces of the lower beings from which the new germ must be made, not having been sufficient changed.

Or we might have reversion from another cause and by another kind, still however depending on a misdirection of forces in the formation of the germ. This theory assumes that man is the resultant of all the life streams found in organic beings. The line even in that case, would be nearly direct through the species named by yourself; consequently in the embryo we should always have traits of the fish, the reptile and the ape, but rarely of the ruminant on the one side, or of the rodent on the other side of that line.5 Ordinarily the organizing atoms of these two classes in entering into the formation of the embryonic molecule would balance each other in their tendencies, and in the fashioning of the human embryo, they will exert their force to cause it to proceed along the nearly direct way through the forms named. But at times through some fault of the constitution of the germ, this might not take place, and we should then have a reversion in the direction of one or the other of these classes. The whole case is something like what would occur with a number of men starting to migrate by successive advances across a wide, trackless and unknown wilderness. From a given point they would start out in many directions, and each division at certain distances would tarry for a while and form a station. Likely no station would be in the line of shortest distance; but at the next advance, a part would go in the direction of such a line, and in the course of time nearly all the travel would be withdrawn from the various diverging lines at first taken, and turned into the route nearest to a direct line   The stations however at first made even by those traveling most directly, would be a little off the line, and in subsequent travel, a shorter road would be taken, cutting off the angles at first made, and leaving such stations in view on one or the other side. The travel with this exception however, would still be along the old path, even after they had reached their destination, because that way had been learned and it would be less labor to continue it than to make a direct one. Yet sometimes a traveler who had previously been journeying to some off-station, would mistake the way, and go to that station again; though his equipment would prove that he had started out to go farther.

Thus it is the embryo never goes through the exact type of lower animals, and that we can have no complete reversions.

Sexual rudiments I suppose to be formed in another way. I suppose the molecule which is to become the new being, to be made up of both male and female atoms, but having an excess of one or the other.

If the excess be male, the molecule will go on to the formation of a male; but the female atoms will at the same time exert their tendencies to form a female, and their product will bear to that of the majority the relation of rudiments. And conversely when the majority are female. If we may further suppose that such atoms are equal in number, an excessive production, say of males, for a time, would be disturbing the balance, produce a subsequent tendency to the excessive production of females, and thus in the outcome equality would be maintained.

The fact that there is generally born an excess of males, I would explain upon the hypothesis that it requires a higher degree of energy to fecundate the female than the male ovule, and that such energy remains expressed in the greater vitality of the female. In accordance with this view I venture the opinion that if it could be ascertained, a majority of blighted ovules would be found to be females and also the prediction—for I am without statistics on that point—that a majority of congenital idiots, and of reversions from incomplete development are also female. I am unable to see, as you essay to show, how natural selection could equalize the sexes.6 Your argument seems to me to imply that if one mother were to produce female offspring, and another male, and these were to unite in pairs—which you fail to show that do not.—the mother of the females would have the largest number of descendents. But I may not comprehend your position.

Nearly a year since I should have published a work on the subject, but I had not the means and publishers were unwilling to issue it except at my risk.

There are many other questions connected with this subject of which I should like to write, but I fear that if you have read even this, I have trespassed too much upon your valuable time.

Still however, hoping that I shall have the honor to hear from you who have already afforded me so much entertainment and instruction | I remain with the highest respect | Truly yours | David T Smith M.D.


Cuttings of the lectures are in DAR 226.2: 34–5.
St George Jackson Mivart was the author of Genesis of species (Mivart 1871a), a critique of CD’s theories.
Melanian: negrito or negroid (OED).
See Descent 1: 124–5 for CD’s discussion of the sutures in the skulls of children and early humans.
In his first lecture, Smith put forward as an argument against CD’s theory of descent examples of apparent human reversion to geese, sheep, and rodents. CD discussed reversion in Descent 1: 122–30.
See Descent 1: 316–17.


Has sent printed reports on his lectures relating to the descent of man [missing].

Discusses his theories on heredity and on the "soul" as the governor of mental and physical development.

Letter details

Letter no.
David Thomas Smith
Charles Robert Darwin
Sent from
Louisville, Ky.
Source of text
DAR 177: 189
Physical description
5pp †

Please cite as

Darwin Correspondence Project, “Letter no. 8634,” accessed on 17 July 2019,

Also published in The Correspondence of Charles Darwin, vol. 20