You are not simply an engineer, a test pilot, an astronaut and a wonderful family man, but then you go over the top and show us that you are a humanitarian, an educator of young and old, a PR man extraordinaire for space programs, a songwriter and a singer. Is there anything you can’t do?? Thank you for helping bring us together as fellow citizens of this blue planet that we all share.

Every day new chemicals are produced by nature. Often just variations on theme (It is highly unlikely that two starch molecules will be exactly alike, each is its own distinct compound in most cases.) but also due tot he complex interactions of enzymes and environment.

PCP is toxic for two reasons. Firstly it is not susceptible to the many breakdown pathways it is exposed to; pathways that usually deal with whole classes of compounds, not individual chemicals they were especially evolved to handle. The liver is a remarkable detoxifying organ for example.

The second reason is it IS susceptible to either damaging cellular machinery or blocking metabolic pathways. The equally artificial hexchlorobenzene is much less toxic not by being more natural, but by lacking the reactive hydroxy group. Hexaflurobenzene is nearly harmless.

[CZ: Either I didn't express myself clearly enough, or you misunderstood my point. The fact that PCP is unnatural is not what makes it toxic. It's part of the reason why PCP doesn't get broken down in the environment. Let me quote from a 2009 review by Copley: "The persistence of anthropogenic compounds is due to their recent introduction into the environment; microbes in soil and water have had relatively little time to evolve efficient mechanisms for degradation of these novel compounds." The whole review is free here.]

@Clint
I understand your skepticism since I shared it on first hearing the results. One portion of my learning to accept that it’s not unreasonable comes from my fooling around in my own genealogy. Nothing special to me of course. Consider a small town in which the parent generation is 128 (which means they’ve got some still-living parents, and they’ve got some descendents, so town has a population of a few hundred).

Now consider that we arrange to have the most disparate possible set of descendents — person number 1 appears _only_ as the parent of people who are also descended from person #2, and so forth. In generation 2, the children of people 1 and 2 only mate with descendents of people 3 and 4 (if they don’t, then people 1 and 2 appear on even _more_ different lineages and the collapse to universal ancestry by someone is even faster). In the first descendent generation, we have 64 different ancestries (parents being 1,2 or 3,4, or 5,6, up to 127, 128). In the second descendent generation, there are only 32 possible ancestries. In generation 7, _everybody_ is descendent of _everybody_ in the original population. At 30 years per generation, this is only 210 years. Since I’m starting to advance in to ‘tough old bastard’-hood, this is slightly prior to the US Revolution, but still nowhere near Charlemagne (ca. 760, 40 generations). And, I remind you, this is the _longest_ span that this initial small town could avoid there being one person who was ancestral to everybody.

Exponentials (true exponentials, not casual speech ‘exponential’, which only means really fast) are hard to deal with intuitively. In 7 generations, any small town that remained isolated would all be related to each other. (This has some relevance to my wife’s family tree. Some to mine as well — there’s an example where 3 brothers married 3 sisters, so the 3 resultant families only have 4 grandparents instead of the 12 you might have expected.)

The exponential growth of ancestors mean that after 14 generations, call it 1600, you’d need a city of population well over 16,000 (2^14)to avoid everybody being related to everybody today. In 1600, a city of population 16,000 was not small.

After 21 generations, say 1390, the smallest city/country, with the most divergent possible mating practices, that could avoid someone being ancestral to everybody is 2^21, or over 2 million. At that time in history, there are no cities this large, and quite a few countries are smaller.

At 28 generations, still far short of Charlemagne (very great grandpa Chuck), say 1180, you have to have a population of over 256 million, and optimal divergent mating, in order to avoid there being somebody who was ancestral to everybody. World population _might_ have been rather larger than this, though not tremendously.

Go back to 35 generations, call it 970 AD, ‘Dark Ages’ Europe, and the population (interbreeding with each other) required to avoid a common ancestry is another 128 times as large — 32 _Billion_ — far larger (about 100 times) than the population of that time, and even far larger than today’s.

The only way to get a date of common ancestry as _large_ as 3400 years (over 100 generations) is if you do indeed have populations relatively isolated from each other for much of that time. The flip side of that is that the sub-populations (Europe, East Asia, the Americas, Africa, …) are even more strongly interrelated.

Fascinating stuff.

Broadly speaking, yes. At the macro scale, some designs (F117) reflect electromagnetic waves diffusely in all directions, trying to avoid a strong reflection in any one direction. While also trying to absorb a considerable amount of energy within the structure. More recent designs tend to align all reflective surfaces, so you only get reflections in certain directions, and again use techniques rather like this viper’s scales to absorb as much energy as possible to make those reflections very weak.