Lifting degeneracy

Some time ago I discussed the idea that Neanderthals were fucked-up because their low effective population size led to inefficient purifying selection. But the usual harmonic-mean effective population size is not quite right: for salvage mutations, things that somewhat correct the wrongness caused by increased genetic load, the effective population size is closer to the average.  In other words, there were probably a lot more Neanderthals during interglacial periods, and these genetic consequences of those population booms ameliorated their genetic problems.

Second, Neanderthal Y chromosomes and mtdNA have even smaller effective population sizes, 1/4th as big as the autosomal effective size, and thus were even more likely to be messed up. which is why, maybe the Neanderthals seem to have picked up mtDNA from some African group closer to modern humans around a quarter of a million years ago: they needed it.

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Luke Blackburn

appears to have done something downright interesting: send vomit-soaked clothes, from people that had died of yellow fever, to various locations in the North during the Civil War, with the intent of triggering yellow fever epidemics. Didn’t work, since as far as we know, yellow fever can only be transmitted via mosquito bite, mainly Aedes aegypti. 

Jeff Davis knew about this effort.

 

 

“They couldn’t hit an elephant at this distance.”

Allen Guelzo wrote a book about the battle of Gettysburg “Gettysburg: The Last Invasion” , in which he says some confused things about smoothbores and rifles. One of my regular readers noticed and mentioned this some time ago.

“Rifling bestowed greater range and accuracy on a musket, but it did so at the price of forming a trajectory for the bullet which “dropped” rather than went straight to a target. To hit a target thus required exact knowledge of the speed and distance of a target, something which in battle was rarely available.”

Which has left Wiki thinking  that rifle bullets had curvy paths while musket balls flew straight.  Not so!

Here’s a decent discussion ( by RogueOne).  The key point is that a spin-stabilized bullet can be pointy yet not tumble: so it has a smaller cross-section and experiences less wind resistance.  So it goes farther.

All the time that the bullet is flying, it’s dropping, under gravity.  If it goes twice as far as a musket ball, that takes twice as long – and it drops four times as far.  D = 1/2 g t^2 – one of the secrets of the Occident, known to but a few.

Guelzo suggests that people couldn’t really take advantage of the rifle’s greater range: but they could.  The Springfield was sighted for 100, 300, and 500 yards – and when 15,0o0 Rebels are coming at you, you have a decent chance of hitting somebody at the greater distances possible with a rifle. Well-trained sharpshooters could even be decently accurate  at those ranges, as Sedgwick found.

Charges didn’t work as well as they had with muskets.

Modern rifles have considerably higher muzzle velocities. Assume that one has four times the muzzle velocity of an 1861 Springfield: then it will take 1/4 the time to reach the same target, and will drop 1/16th as far. A flatter trajectory.  How do we do it?  Velocity !

 

 

 

 

 

Reverse salients

Edison thought in terms of reverse salients and critical problems.

“Reverse salients are areas of research and development that are lagging in some obvious way behind the general line of advance. Critical problems are the research questions, cast in terms of the concrete particulars of currently available knowledge and technique and of specific exemplars or models that are solvable and whose solutions would eliminate the reverse salients. ”

What strikes you as as important current  example of a reverse salient, and the associated critical problem or problems?

 

 

 

 

Sensitive Detection of gene flow

One problem with arguing with ignorant people is that they don’t usually have indicator lights that tell you exactly how ignorant they are.  This matters when you’re trying to explain something: it’s not always clear  how much goes without saying.

About the imaginary high levels of gene flow between distant populations in the past: if that had happened, Fst between those populations would be close to zero.  It’s not. And when an inevitable consequence of a certain proposition is false, the proposition is false.

But here’s another example: falciparum malaria probably originated in Africa ( it’s closely related to a kind of malaria that infects gorillas). At some point it spread to humans, and it’s a bear – in terms of evolutionary pressures, probably the worst disease in the world.

Many different expensive genetic defenses have arisen in populations exposed to malaria. But those seen in southeast Asia/PNG are, at the molecular level, entirely different from the ones seen in  Africa. As far as I know, there is no overlap at all. You see mutations of the same gene showing up in those far-separated populations ( convergence) , but the SNPs are never the same.

The sickle-cell allele would have been advantageous in, say, PNG lowlands, and if even a few copies had ever arrived there, it would have become common rather rapidly. A smidgen of gene flow from sub-Saharan africa , even 20 individuals total, would have left a genetic signature in PNG. [ just as a few copies of Denisovan altitude-tolerance alleles were enough to transform Tibetans]  That smidgen would have grown geometrically with time: it would function as a very sensitive detector of African gene flow.  But it never happened. Contrariwise, some of the malaria defenses in PNG ( like Melanesian ovalcytosis)  would have spread widely in Africa with even a little gene flow.  But that never happened either.

 

 

Ashkenazi PRS

There are now a couple of surveys with Ashkenazi EA polygenic scores.  We don’t know that the populations were representative, but probably they weren’t far off. Scores correspond to an IQ of about 110. Personally, I’m still pulling for 112.

A fair number of people publicly disagreed with our Ashkenazi hypothesis.

They were wrong.

 

 

Herbert West

Just ran into an interesting question from a biology problem set:

” Using the laws of thermodynamics, explain why it’s impossible to re-animate organisms that have died ( making Frankenstein’s monster and zombies impossible so we don’t have to worry about a zombie apocalypse.) “