1. What is truth?
Truth is a matter of plausibility.
2. Why is the sky blue?
The sky is blue because so many other things are not blue.
It is fantastic that something so large and so dominant in our lives has such a bright colour. Shouldn't our vision perception centre around it so that we only see a neutral shade? This would be the case if plants any animals didn't contain such luminous greens and saturated reds.
All of these colours have come to be perceived as roughly equal (although with a slight bias because the Sun is green), and so if they are mixed together the colourless colour we expected for the sky will be seen.
3. Why do women from the USA have square jaws?
During the colonisation of the North America sub-continent, Europeans were living in comparative ease compared to the difficulties faced by the Pilgrims and pioneers of the New World.
During the first hard winters, the more delicate settlers had a smaller chance of staying alive. This evolutionary pressure produced the white North American's characteristic sturdiness over the first few generations, and it has remained since.
4. Why do people blush when embarrassed?
Humans are animals which evolved in a social and hierarchic system.
In a hierarchic society, members will necessarily change position and some mechanism must be in place for this to occur, and this is some kind of confrontation, or fighting. As an aside: fighting seems to be a good way of establishing levels; it uses physical strength and well as tactics and quickness of wits, all of which were highly important when humans were hunter gatherers on the savannah. The emphasis has changed somewhat now.
However, a creature which fights to the death to find their position in society is not going to survive to take that position nor to pass on their genes. A kind of formalised confrontation evolves, and can be seen in many species. Although injuries are made, there is some kind of action of surrender in place. For example, dogs roll onto their backs to show they will stop fighting.
When people are ready for confrontation, the 'fight-or-flight' reflex activates. The body moves blood to the muscles to make them faster and more effective (this is why your stomach contracts when you are scared; the blood has been redirected).
In a ritualised fight been two people, the only true sign of submission would be the cancellation of fight-or-flight. An arms war of false submissions would probably occur before the true sign was found since evolution would favour the person who claimed to submit only to make a new attack when the other's guard was down.
The only sign taken as genuine would be a direct indication that the blood has been moved away from the muscles and the body is not prepared for action - that is, blushing. When blood is at the face, it cannot be powering the muscles.
When we are embarrassed we have been involved in some kind of confrontation and do not want it to continue. The blush is the remnant of the formalised submission of our ancestors.
5. Why do some people wear clothes?
To keep warm. Why do some societies uniformly wear clothes even when it's warm?
The fact that individuals don't feel 'bad' but instead feel 'ashamed' (shame or embarrassment is a group phenomenon) when naked implies that the wearing of clothes is a social more. (Aside: That small children don't feel that shame implies that either the ability to feel shame doesn't develop until later in life, or that the pressure against being naked is memetic rather than genetic and it takes time to be socialised.) Now the question is: How did clothes move from being an environmental necessity to a social construct?
Clothes have been the peacock's tail of human society (that is, a person may demonstrate their status by showing that they are able to spend resources on unnecessary rather than essential items). Society needs this kind of competition to function and self-organise. A fit (in the Darwinian sense) society will allow no alternatives, so the social pressure is not against being naked, rather it is against non-participation.
People wear clothes because to not is to deny their social nature.
(Originally posted at interconnected.org/truth in 1999. The final two are too explained, too plausible, and not playful enough. The two before that are how I should have continued the series. I keep meaning to write a children's questions & answers book, and should get back to it.)