Sixty-one years before Charles Darwin published "On the Origin of Species", and Sixty-seven years before Gregor Mendel published "Experiments on Plant Hybridization",

Edward Jenner could have predicted that the cessation of the smallpox vaccination program would enable mpox to become more virulent and spread:

"The deviation of Man from the state in which he was originally placed by Nature seems to have proved to him a prolific source of Diseases.

From the love of splendour, from the indulgences of luxury, and from his fondness for amusement, he has familiarised himself with a great number of animals, which may not originally have been intended for his associates.

The Wolf, disarmed of ferocity, is now pillowed in the lady's lap.

The Cat, the little Tyger of our island, whose natural home is the forest, is equally domesticated and caressed.

The Cow, the Hog, the Sheep, and the Horse, are all, for a variety of purposes, brought under his care and dominion.

There is a disease to which the Horse, from his state of domestication, is frequently subject.

The Farriers have termed it the Grease.

It is an inflammation and swelling in the heel, from which issues matter possessing properties of a very peculiar kind, which seems capable of generating a disease in the Human Body (after it has undergone the modification which I shall presently speak of), which bears so strong a resemblance to the Small Pox, that I think it highly probable it may be the source of that disease...

...May it not, then, be reasonably conjectured, that the source of the Small-pox is morbid matter of a peculiar kind, generated by a disease in the horse, and that accidental circumstances may have again and again arisen, still working new changes upon it, until it has acquired the contagious and malignant form under which we now commonly see it making its devastations amongst us?

And, from a consideration of the change which the infectious matter undergoes from producing a disease on the cow, may we not conceive that many contagious diseases, now prevalent among us, may owe their present appearance not to a simple, but to a compound origin?

For example, is it difficult to imagine that the measles, the scarlet fever, and the ulcerous sore throat with a spotted skin, have all sprung from the same source, assuming some variety in their forms according to the nature of their new combinations?

The same question will apply respecting the origin of many other contagious diseases, which bear a strong analogy to each other."

-Edward Jenner
An inquiry into the causes and effects of the variolae vaccinae: a disease discovered in some of the western counties of England, particularly Gloucestershire, and known by the name of the cow pox

Published in 1798

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