Also:

"Paraquat is the chemical name for the active ingredient in Agent Orange."

In reality, paraquat is very different from the active ingredients in Agent Orange (2,4-D and 2,4,5-T).

For instance, a molecule of paraquat contains 2 nitrogen atoms and no oxygen atoms whereas a molecule of 2,4-D or 2,4,5-T contains no nitrogen and 3 oxygen atoms.

The only similarity between them that I know of is that they are both used as herbicides.

The author seems to be confusing the US government's use of agent orange in Vietnamese jungles, with their use of paraquat on marijuana farms in Mexico in the 70s.

Thank you for the correction. I was relying on my memory rather than looking up the chemistry. I regret that I'll have to remove the reference to the US atrocities in Vietnam, but I suppose I'll take that up another day...

Also if you look at the skin of older people from a sunny place compared to the skin of people from an overcast place, it's noticeably tougher and more wrinkled.

I'm an Australian who has lived the last ten years in the UK and my older Australian relatives definitely have older looking skin than my husband's UK-based family.

Plus the rate of skin cancer is definitely higher in Australia. It is a real public health issue there.

You are correct, however remember that nice thing called the Ozone Layer Hole which affects the southern hemisphere

And actually, most "older people from a sunny place" you mention did not have their evolutionary roots there.

And yes, tougher and more wrinkled, but less incidence of malignant cancers (but might be because of that first item I mentioned)

Also:

"Walking around with a 40-pound backpack has the opposite effect of carrying an extra 40 pounds of belly fat."

Actually walking around with a 40-pound backpack is a bad idea, as compared to carrying the weight at the level of your belly (all other things being equal) because the risk of back damage is much higher.

Right. Belly fat is stored there because a central location is best for the body (although it was sufficiently rare in our evolutionary ascent to afford 40 pounds of belly fat that our bodies didn't adapt well to it, which is why it's so bad for us). In terms of structural imposition on the body, the backpack is worse.

Incidentally, anyone who's hiked will tell you that the best position for heavy weight is at the very top of the pack. The reason is that this puts most of the weight on your hips rather than your back.

Women seem to prefer weight lower in the pack than men, even if equal height, because of a generally lower center of gravity. I nearly broke my nose carrying a male friend's pack briefly while hiking -- tripped on a tree root and was so unused to the high center of gravity that I smashed my face into the ground. My own pack was heavier (yay food!) but sized and packed very differently.

Shouldn't it be at the bottom of the pack then ?

No, the bottom of the pack is completely outside (behind) the hips. If you put it at the top of the pack, you'll naturally bend forward slightly to an equilibrium between your torso and your backpack, the top of the pack will be roughly above the hips.

Exactly why you see the head basket carrying in many countries that have to do long haul water carrying.

What I meant in my other comment is: can you help me figure out how to map structural imposition to lifespan probability in a meaningful way?

How about wearing a diver's weight belt? The weight is all at your hips and is more or less equally distributed between front and back.

Completely different physics, because buoyancy cancels out gravity. The weight belt is distributed around your center of mass because it has different buoyancy (higher density) than you, but subject to the same gravity, and you don't want it affecting your orientation underwater.

Even if this was true it's ridiculous when taken as evidence for radiation lowering cancer risk:

Survivorship bias (or survivor bias) is a statistical artifact in applications outside finance, where studies on the remaining population are fallaciously compared with the historic average despite the survivors having unusual properties.

http://en.wikipedia.org/wiki/Survivorship_bias#As_a_general_...

Yes, thank you. Breast and thyroid cancer studies on Hiroshima survivors show HIGHER rates. This was a blunder on my part. I've removed the paragraph on Hiroshima.