Pleasant exchange with Dr. John Casti:

Not long ago I wrote Dr. Casti to tell him I liked his book and thought he might be interested in my own observation.  I sent an attachment with some graphs I thought he might be interested in.  His book is full of excellent graphs.  He was kind enough to respond and insert his remarks in the text I sent him.  I liked what he had done.  A different perspective is of enormous value when one is searching in a new field, and I thought what he had to say was so good I asked him for permission to post my message to him along with his remarks.  He agreed and then encouraged me to add my own remarks to his.  So what you have below is my message to him with his remarks in blue and then a short reply from me. 

MY MESSAGE TO HIM WITH HIS REMARKS.

I am including three graphs that might interest you in support of my contention that birth rate is determined by kinship rather than choice.  This is a small fraction of the data I have posted on nobabies.net, but they have the advantage of being drawn from published professional articles and of requiring less hand waving than much of the other data.

 


This graph is from On the Regulation of Populations of Mammals, Birds, Fish, and Insects, Richard M. Sibly et al. SCIENCE vol. 309 no. 5734  JULY 22, 2005 page 607 – 610. 

The group analyzed over a thousand serial field counts of animals and found this pattern consistently.  Most people think that animal populations are limited by the environment (well, whatever “most people” believe is almost always wrong, so there is no surprise here, at least not to me), but as you see the graph does not fall rapidly as the break even point is reached but continues to level off (but at a negative growth rate, so presumably population still then declines).  Since this is not due to the females putting off having babies so they can pursue a career, it seems that average kinship (the inverse of population pool size) is the determining factor.  You might still invoke mood, assuming animals have a community mood as people do. Certainly mice undergo a behavioral change during natural “plagues” of mice in which the population goes up very rapidly; the males stop defending their own females.  Still since the pattern is so consistent, it seems more plausible that kinship is the critical factor.
(this is certainly possible, although very difficult to test, one way or the other. My own thoughts for what they’re worth are that the more social the group, the more likely it is to have a “social” mood, and more importantly, the more that mood then biases the events that occur within the group. Whether this is true for births is a specific instance of an event, and I just don’t know. Personally, I do not regard annual births or birth rates as a very good measure of social mood anyway, even in humans, so it is probably even less important in non-human animal populations.)

This graph is from a study done in Denmark where they compared marital radius – the distance between birthplaces of a couple – with the number of children. 

Graph taken from Comment on “An Association Between the Kinship and Fertility of Human Couples,” Rodrigo Labouriau and António Amorim SCIENCE vol. 322, December 12, 2008 page 1634b.  Vertical axis is number of grandchildren.  Horizontal axis is distance in kilometers between the birth places of the parents.

Since this was a cohort, community mood is constant.  Assuming that people in neighboring villages are more likely to be kin in an ancient settled land than people in distant villages, kinship seems again to be the critical factor, just as with humans
(I wonder whether this principle would extend to a much larger, far more mobile country like the USA?)

This next graph is taken from a Genealogical article from Iceland.

The vertical axis is some measure of the number of children.  The horizontal axis is kinship, second cousin or closer then third cousin or closer and so forth.  The highest fertility is for second cousin or closer, in other words first cousin once removed.   An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 - 816.  Again this is a cohort study so mood is not a variable.  The people probably didn’t even know whether they were 5th or 6th cousins, but their family size “knows.”  Look how tight those error bars are.  They are two standard deviations.

(This is an interesting observation about actual knowledge of the relationship you have to a mating partner. This result would suggest that there is some kind of kinship signaling taking place that goes outside the usual methods of everyday speech, interaction , etc.)

And now my reply to him. 

Many thanks for your reply.  Your remarks are all excellent.  Let me bounce a couple of them back to you. 
1. Concerning  mouse plagues:

(this is certainly possible, although very difficult to test, one way or the other. My own thoughts for what they’re worth are that the more social the group, the more likely it is to have a “social” mood, and more importantly, the more that mood then biases the events that occur within the group. Whether this is true for births is a specific instance of an event, and I just don’t know. Personally, I do not regard annual births or birth rates as a very good measure of social mood anyway, even in humans, so it is probably even less important in non-human animal populations.)

I take your point.  I do have an idea, though.  The time course of the population during mouse plagues seems to have a characteristic pattern.  I am working on a computer program that is based on a genetic assumption.  If I can get the program to work before it drives me stark raving mad (assuming that has not already happened) I hope to be able to duplicate the same curve.  I'll let you know how it goes. 

2.

Concerning marital radius.

(I wonder whether this principle would extend to a much larger, far more mobile country like the USA?)

I doubt it.  Years ago I'm sure it was true but we are so mobile now and the effect fades by the time 100 kilometers is reached.  Maybe there are still parts of Appalachia where things are old fashioned but it's hard to believe.  The growth industry there is mountaintop coal mining.  They chop the top off a mountain, take the coal and dump the tailings into the valley.  The only objection so far has been because it's bad for the fish.  I think it's probably bad for the communities that used to live on those mountains. 
3.Concerining the Iceland study.

(This is an interesting observation about actual knowledge of the relationship you have to a mating partner. This result would suggest that there is some kind of kinship signaling taking place that goes outside the usual methods of everyday speech, interaction , etc.)

That is something I hadn't thought of.  I just assumed there was no way they could know how kin they were and the birth rate only reflected the kinship they actually had.  On the other hand, if they CAN sense kinship somehow, that would mean that it might be possible to salvage most of the world.  I had pretty well given up hope. 

Again thank you for your illuminating perspective,

AND NEXT, is an excerpt from my letter asking permission to show you this:

“I am still pleasantly hauted by your comments.  If it seems good to you, I would be happy to post what you sent me on nobabies.net.  I'd leave off my own responses since I don't think they add much.  Of course I won't do it without your encouragement since it is your work and not my own.”

He gave me the permission but also encouraged me to include my side of the conversation, and so I have.

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