September 11, 2018

Svante Pääbo
Director. Max Planck Institute for. Evolutionary Anthropology
Deutscher Platz 6
04103 Leipzig
tel: +49 341 3550 501

Dear Dr. Pääbo,

As is the rest of the world, I am thrilled by your work on the Denisovian-Neanderthal girl.  The question arises as to whether, had she grown up, would she have been fertile.  I can tell you how to find out, and it has nothing to do with genes, which seem to have been working fine for her; it’s epigenetic.

A recent advance in AI arranges to have a deep learning program to become bored when it stops learning and to change the approach.  In contrast, when a human learns something new the reaction is to lose sphincter control and run away squealing.  If that is your bent, spare yourself and start now.  Otherwise, if you are willing to learn, I shall lead you in quite the galliard. 

Selection of an animal species for a new niche is a time contest against other animals.  Speciation raises the possibility that the animal may keep its legacy niche and also seize the new one, so speciation is also a contest and is long delayed only at peril.  But rapid speciation entails, because of Mendel’s laws, a cap on population size so there is intense selective pressure to have a mechanism that maintains a population at some moderate size.  The effect of such a mechanism has been documented in 1700 field studies compiled by Richard Sibly; there is a curve of fertility against population size such that below a rest point fertility rises rapidly and above that point fertility falls slowly.  The Sibly curve can be seen in humans in Iceland and Denmark, where it has also been shown that once issues of kinship are taken into account, there is no effect of education nor income on fertility; dismiss choice from your mind.  It is superstition. 

A population much displaced from the rest point goes extinct by inbreeding depression or what amounts to outbreeding depression.  Throughout Western history the almost invariant cause of societal collapse occurs through outbreeding depression within some 300 years; in the far East dynasties follow the same time course although societies are durable. 

The cause is epigenetic and my own lab work suggests it is mediated by methylation of DNA, such that mismatch accumulates over generations until an element of pre-zygotic infertility develops followed by the mercy blow by post-zygotic.  Rich countries have since many years past reached the saturation point of pre-zygotic and are now marrying later and later; when women no longer marry before menopause the babies will stop and, in a few decades, a high-tech civilization will become unsustainable, with consequences terrible in the extreme several years before global, total infertility supervenes.  The process may be hastened by the fact the dose of folic acid given women, at least in this country, is sufficient to suppress fertility in fruit flies via the same epigenetic mechanism that is deadly in large random mating human populations. 

You can find all this expanded and references at looking at the first 32 links or if you like I would be most happy to send you a DVD of the whole sweep in Word. 

To learn if your 13-year-old girl was fertile will take some effort.  You’ll need to run down just where in the genome the relevant methylation sites are.  A computer program you will find in one of the links models the process and may help.  I can also add that my work with the program suggests that all those sites are bunched up on two or four chromosomes; to reduce noise, you might want to have blocks of 10,000 sites rather than 100 as I do.  Once you have worked it out in living humans you should have enough to be able to look at the methylation pattern of the girl.

Good hunting. 

M. Linton Herbert MD

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