June 17, 2012


Dear John Casti:
Vienna, Austria

After months of eager waiting I have now received your book X-Events: the Collapse of Everything, (Harper Collins New Your, 2012) and read it with pleasure.  We communicated after I read Mood Matters, which I also found interesting and valuable, and if your memory has the impressibility of water and durance of iron, you probably know everything I am about to say.  But I make bold to write again so as to include my faithful, long suffering web site followers.  Consider this a shameless plug for your book.

In Mood Matters you point out an inescapable correlation between economic growth, general hopefulness, fertility and some other things and demonstrated that such things cycle as well as correlate.  The one thing that cannot be an effect of any of the others is fertility.  This is due to mating strategy and mating strategy alone. 

On the Regulation of Populations of Mammals, Birds, Fish and Insects, Richard M. Sibly, Daniel Barker, Michael C. Denham, Jim Hope and Mark Pagel SCIENCE vol. 309 July 22, 2005 page 609

An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816

Human Fertility Increases with marital radius. Rodrigo Labourian and Antonio Amorim.  GENETICS volume 178 January 2008 page 603

Comment on “An Association Between the Kinship and Fertility of Human Couples,” Rodrigo Labouriau and António Amorim SCIENCE vol. 322, page 1634b December 12, 2008

Marry cousins to have an adequate number of children.  All right, maybe consanguineous courtship is a result of other factors you deal with.  But fertility is at least mediated by mating strategy, and as such can be predicted. 

Prediction becomes problematic in X-events.  You define them as important events that are so far from the usual distribution of events as to make them unexpected, even unprecedented.  But of all kinds of futurology, demographics is the most tractable.  One thing you can say is that most people who will be alive in ten years are alive now and most people alive now will be alive in ten years, barring X-events.  So l looked at what you were doing with demographics.

One obvious number is that there are seven billion people in the world.  That’s too many for my comfort.  It’s a lot any way you look at it.  There will be resource depletion, pollution, environmental change and conflict simply because with that many people a lot of people are going to be doing anything people are capable of doing. 

A second point is that in your book you describe a number of processes, each perhaps unlikely but in aggregate a significant hazard, that might throw us abruptly into the technology of the nineteenth century.  But it won’t be like it was the last time.  With that technology you can only feed two billion people on the planet.  With seven billion, once strategic food reserves are depleted or withheld, more people will starve than the world ever saw at anytime prior to the twentieth century. 

But I suppose your book is overloaded with shock value as it is, and a careful analysis of what people will do in extremis (Remember the Donner party.) might have made the book unpleasant.  So I happily accept your judgment. 

The third point is that, while there are clearly too many babies, they do not seem to be showing up in the places where they are most needed and where their needs can best be met.  The developed world is “aging,” which is a euphemism for dying.

Take Austria since you are there.  Here is what the birth rate has been doing for the past few years:


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Definition of Birth rate: This entry gives the average annual number of births during a year per 1,000 persons in the population at midyear; also known as crude birth rate. The birth rate is usually the dominant factor in determining the rate of population growth. It depends on both the level of fertility and the age structure of the population.

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In case you are wondering whether that is a lot or a little, here is the number of children a woman would have in a lifetime as of 2011:  1.4
downloaded June 17, 2012

Now there is the kind of number you can get your teeth into.  The prediction, “Things are going to change,” seems hard to escape. 

In fact regime change, the fall of an empire, is not an X-event at all.  Here is a link to some numbers I put together last year for a genetics conference.


Scroll on down, or use your edit function to jump down to “Chinese dynasties.”  Then read a few graphs.  The fall of empires is quite humdrum, predictable as the dawn.  Barbarians coming through the gates and doing unpleasant things may seem important at the time, but it’s just business as usual.  The timing is accurate to about a generation.  Stop marrying cousins and there will be consequences.  (Of course the elite of empires stop marrying cousins; establishing alliances seems far more important at the time.) 

This time of course it’s different.  We have the science.  We have the statistics.  We have no excuse.

All the best, and thanks for a nice read.


Linton Herbert
Dr. Casti was kind enough to reply and even gives me permission to post his reply, so here goes:

Hello Linton,

Thanks very much for your as always thoughtful message and for the kind words about my new book X-EVENTS. I'm glad you enjoyed it, and I'm especially glad that it sparked some thoughts in your brain about some of the issues I raised. I very much appreciate you also giving the book a plug on your web site.

In regard to your remark about regime change not being an X-event, I want to point out that the notion "X-event" is not a black-or-white affair. This is why the list of 11 examples in Part II of the book range across a huge spectrum of time scales going from a few milliseconds (an EMP) to many years (deflation, peak oil). The main point is that an X-event is one that is (a) rare (we don't have much data on their occurrence), (b) surprising (when they happen we're always shocked and almost always unprepared), and (c) have great social impact (positive or negative, although I focused on the negative for the reasons I state in Part I of the book). So I think a case can be made for *some* regime changes as indeed being X-events, while others are not.

As for demographics, I agree completely that this is one area of social science where predictions can be made with some confidence, although even the forecasts made by people like my former IIASA colleague Wolfgang Lutz can be turned upside down by an X-event of a high enough degree of "X-ness", such as a worldwide pandemic or a global nuclear holocaust. In fact, I personally believe that the outline of the complexity theory I present in the book will give us some advance warning as to exactly when such an X-event is becoming more rather than less likely. Such events are (human) nature's way of redressing a complexity gap that's gotten out of balance.

Well, I could go on like this for quite a few more pages. But why bother, since I've written a 300+-page book that tells the story even better, with another 300+-page book in the wings waiting to tidy up some of the missing details.

Again, many thanks for writing. It's always good to hear from you.



And many thanks to you, too.

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