Semi-Daily Journal

"So you share 1/256 of your genes with Maddy inherited from John Anderson Lord"

Isn't there a big difference between stating the probability of sharing a particular gene and stating that you actually share that fraction of genes?

From what I remember of biology, each person carries two copies of a gene and you randomly get one of the two from both parents.... so your dad could have by chance given you 70% from his other parent and only 30% from the decendant of the GGParent under consideration.

Hmmm. Not Socrates. Many of his dialogue partners, e.g., Hippias, were profoundly irritated by Socrates. Maybe "Numerically Endowed Dad" might be a better moniker... ;-)

Well this is sort of related at least.
http://www.nytimes.com/2003/03/08/opinion/08WATT.html
Remember the number 1.85. It is the lodestar of a new demography that will lead us to a different world. It should change the way we think about economics, geopolitics, the environment, culture — and about ourselves.

To make their calculations orderly, demographers have typically worked on the assumption that the "total fertility rate" — the number of children born per woman — would eventually average out to 2.1. Why 2.1? At that rate the population stabilizes over time: a couple has two children, the parents eventually die, and their children "replace" them. (The 0.1 accounts for children who die before reaching the age of reproduction.)

Now, in a new report, United Nations demographers have bowed to reality and changed this standard 2.1 assumption. For the last five years they have been examining one of the most momentous trends in world history: the startling decline in fertility rates over the last several decades. In the United Nations' most recent population report, the fertility rate is assumed to be 1.85, not 2.1. This will lead, later in this century, to global population decline.

In a world brought up on the idea of a "population explosion," this is a radical notion. The world's population is still growing — it will take some time for it to actually start shrinking — but the next crisis is depopulation.

The depopulation time bomb is fortunate since it looks like climate change will radically increase sea levels and we'll have no place to live :).

I thought most of our genes are identical or at least don't come in thousands of varieties. My guess is that even total strangers share more genes than Brad's calculations would suggest for siblings.

Can't help but start thinking about the effect of depopulation on K/L, and thus productivity and per capita GDP. What is the crisis? Increasing wages? Labor scarcity? There is a theory that it was the plague that brought us out of the dark ages. (By making labor relatively scarce and thus increasing wages.) National and world GDP may drop, but it is per capita which matters to individual well-offness. (Growth may slow if Julian Simon is right about "brainpower", though)

I agree we would be better off with a lower population. Land is about the only thing improved technology can't help us with. I'm optimistic on brainpower too since technolgy might help that directly or indirectly free up resources.

But one has to be careful when analyzing exponential growth based on an average....

Imagine equal amounts of two types of bacteria in a dish, with plenty of room to grow. One grows at 20% per day, the other is not doing well and shrinks 20% per day. The growth rate for the next day is 0 since the rates cancel. But the long term growth rate is 20% as the thrivers dominate. There are definitely population subgroups which have strong beliefs that they should have large families and are somewhat successful (so far) at passing on these values to the next generation. And the change is not slow. One generation can double or triple from the next.

It really depends what you mean by "the same" genes. I tried to make it clear by referring to genes all of them copied from the same genes in one particular ancestor...

But, yes. We share 98.4% (or whatever) of our genes with your average chimpanzee, and 40% (or whatever) of our genes with your average banana...

I really love these mathematical articles. Please keep them coming.

Kilroy

I think it *would* be more fun if your children were mutants. More precisely, half-banana half-human mutants (which, of course, given 40% banana/human gene commonality, would really be 70% human and 70% banana), and whenever someone was complaining that his spoon is too big, one of them could walk up to him and say "I am a BANANA!"

Err... right?

Channeling "Rejected", Julian?

On matters of population, I do think that Wattenberg is too quick to miss the downside issues. Although fertility rates are sinking, that doesn't necessarily mean that growth rates will, as well; smaller families will be offset by shrinking death rates, so it's a question of which stat will outpace the other.

Although the current U.N. forecasts are slightly more optimistic, they're nothing to write home (or an op-ed) about; looking at the projections from 2003 to 2025, both the less- and least-developed nations will increase their relative share of the population, while the more-developed nations and China will reduce. Strikingly, the more-developed nations will have a population increase of about 3% and China of about 10%, while the less- and least-developed nations will grow by 24% and 38%, respectively. That's a whole lot of immiseration (in the dictionary, not Marxian, sense), assuming that there isn't some sort of sudden affirmation of Rostow in the works.

Bear in mind that we receive our genetic inheritance in 46 packages -- chromosomes -- with each parent providing half. Thus 1/128 of one's genetic heritage from a given ancestor is not a helpful concept. Either you get at least 1/46, or you get nothing. The question should be, "What are the odds that you share at least one chromosome, inherited from the common ancestors, with a given third cousin?" This also means that barring serious inbreeding, we each have ancestors no more than six generations back from whom we inherit no genetic material. That puts the concept of "direct ancestor" in a different light.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Meiosis.html

I'm no expert on this, but apparently there is something called crossing over which scrambles the genes somewhat.

If memory serves, the kid *is* a MUTANT -- the average human has ~1 mutation.

For better or worse this doesn't give the kid X-powers or anything.