January 30, 2010

Professor Gary Churchill
The Jackson Laboratory
600 Main Street
Bar Harbor, Maine 04609

Dear Dr. Churchill: 
I had read somewhere of your work in creating a large number of strains of highly diverse mice for laboratory but did not have your name, so I was delighted to read Mouse Mash-Up, Megan Scudallairi SCIENTIFIC AMERICAN vol. 302 no. 2 February, 2010 page 18.  There is something I would like to know, and perhaps you have the answer already in your head. 

It is generally assumed that greater genetic diversity is always good in humans.  But the facts speak otherwise.  The included DVD will give you the evidence that even a rather small increase in diversity has a profound effect on fertility, with even couples who are of the same nationality and related as closely as the equivalent of 6th cousins have fewer children and grandchildren than couples who are nearer kin.  I oversimplify, but that is the bottom line. 

From what I have been able to put together, people who live in a large and diverse randomly mating community have a catastrophic fall in fertility in about 10 generations.  There even appears to be a crisis in only 5 generations.  I have not seen numbers for the rate at which immigrant families have fewer numbers over a few generations, but informally from conversations even in three generations the fertility rate is far less than it was in the old country. 

You have a collection of 8 diverse mouse lines that together represent 90% of human variability.  So what happens when you combine them all over 3 generations?  There should not be a total collapse of variability; even humans seem to be able to survive that degree of out-breeding, but I think there might well be – nay I am pretty sure there will be – a significant fall in fertility as measured by litter size.

Possessing the eight founder lines, it would seem logical for you to ask, “What happens when we make the grand mix?”  If not, then it would only take a few months, a few cages and a few pounds of chow to find out. 

I have heard of this being done in rats, but am unable to get a reference.  The project was apparently called “Ratopia.”  Some enthusiast raised an enormous number of rats all together in the same room, providing them with places to perch and all the food they wanted.  The rats starved, fought each other and eventually became so infertile they died out.  Fighting tapered off as crowding diminished but fertility did not return.  If I had a reference, I would be delighted.  There are details I really need to know, particularly how long it took for fertility to fall. 

Infertility is becoming more and more recognized as a human problem worldwide.  Some of this infertility is due to birth control, but it seems clear that this is not the whole story or even most of the story.  My evidence is that churning up the gene pool is capable of doing it and has done it any number of times in the past.  However so far I do not have an animal model that would serve as a model.  You could make one quickly and easily.  If you have not done it and are not disposed to do it, please let me know how.  (I have never raised mice and do not know how much your eight lines would cost.)  Of course the word would be far better received coming from a recognized expert.

I have posted what information I have (and still post as information comes in) along with my correspondence on my website NoBabies.net.  If that is not sufficient, or if you have any question at all or I can help in any way, please get in touch with me.  I include a copy of the C language program I wrote that models the underlying gene interactions and compares fertility with population size. It’s Linton 2 on the black CD and runs on a Windows XP platform, 2 gigs RAM, at least dual processors for heat load.  Suggested parameters are at the end of the big chart in the Brisbane poster on the CD. 


M. Linton Herbert MD

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