Sir/

In response to your letter in the Agricultural Gazette of the 15 Feb^y permit me to state that I have for some time had my attention drawn to a theory or principle on the balance of the sexes which bears on your enquiry & which may perhaps tend to illustrate the subject¹

I addressed a note to the Ag^l. Gazette a few weeks ago drawing attention of graziers & farmers to what seems to be the law of nature, by which the sex of the progeny is determined, which if clearly understood & confirmed will enable the breeder to arrange what proportion of either sex his stock shall produce²

The principle is simply that nature which takes the utmost pains to secure the reproduction of her creations will cause the first products of generation to follow the sex of that one of the parents whose constitution is oldest (from age or infirmity) & is therefore likely to die first

Having seen this principle stated above 30 years ago I have amused myself in tracing its results in man & animals & with almost invariable certainty.

For instance the known fact that males of the human species predominate in the proportion of 18 to 17 over females which is quoted by Paley & others as a special arrangement by Providence to provide against the casualties of war &c may by this rule be easily accounted for as on an average of marriages men largely exceed their wives in age³

Throughout the families of my acquaintance I can remember but one decided failure in its application. In others there have been apparent failures but explained by the after knowledge of facts in their physical condition e.g. one young wife of an elderly person produced a daughter but it turned out she had an open ulcer in her leg   In two similar cases the wife had a family of daughters, the cause being that whilst in childbearing she was in delicate health but after that period they recovered their former strength of constitution

When the folks on the Stock Exchange were betting about the sex of the expectant offspring of Louis Napⁿ. I stated my opinion without hesitation that it would prove a son.⁴ In my own case I applied this rule successfully when putting a favorite mare to a blood horse—& I have known a friend exclaim—against his ill luck in always having a bull calf when he had permission to send a cow cost free to a very celebrated old bull—whereas if he had sent a cow older than the sire he would doubtless have had a heifer calf

One apparent exception was pointed out by a gentleman—a large breeder, in the fact that the first calf of a young heifer is generally a cow calf

This I attributed to the circumstance that, the cows running indiscriminately (in Australia) with the bulls the heifers took the bull before they had themselves arrived at full maturity & whilst their constitution was therefore weaker than that of the male.

The authority in which I found the statement of this theory was a volume of lectures on Political Economy by J. Bryan Esq^re delivered before the Royal Society of Dublin about 34 or more years since⁵

I have heard also that M^r. Coombe⁶ has made allusion to it

I hope shortly to make fuller reference to these authorities when I am able to pay a visit to the British museum & to communicate any further information if deemed by you of sufficient interest to the particular subject of your present enquiry

I remain | Sir | Faithfully yours | W^m. Henty

Cha^s Darwin Esq^re | &c &c