As the 1935 Boy Scout handbook says, "By agreement of the Scout Leaders throughout the world, Boy Scouts greet Brother Scouts with a warm left hand clasp." (wikipedia). But what's the origin of this form of greeting?
Lord Baden-Powell, founder of the Boy Scouts, claimed he learned the custom from a defeated African chieftain whom he attempted to greet in 1896 by holding out his right hand. The chieftain supposedly replied: "The men in my tribe greet the bravest with the left hand." There are different versions of this story, but I think all of them can safely be dismissed as bogus.
There's also a theory that the scouts shake with their left hand because it's the hand closer to the heart. I also doubt this theory.
I think the real origin traces back to Baden-Powell's passion for promoting ambidexterity — and not just the ability to use either hand with equal dexterity, but to use both hands for different tasks, simultaneously.
To train the human body completely and symmetrically, that is, to cultivate all its organs and members to their utmost capacity, in order that its functions may also attain their maximum development, is an obligation that cannot safely be ignored. This completeness and symmetry can only be secured by an equal attention to, and exercise of, both sides of the body--the right and the left; and this two-sided growth can alone be promoted and matured by educating our two hands equally, each in precisely the same way, and exactly to the same extent.
It is hardly possible to lay too much stress upon this bimanual training, or to attach too much important to the principke, because our hands -- and our arms, from which, for purposes both of argument and education, they cannot be separated -- not only constitute our chief medium of communication with the outer world, but they are likewise the pre-eminent agency by which we stamp our impress upon it...
The heavy pressure of my office work makes me wish that I had cultivated, in my youth, the useful art of writing on two different subjects at once. I get through a great deal extra -- it is true -- by using the right and left hand alternately, but I thoroughly appreciate how much more can be done by using them both together.
The ceremony of bone pointing is a common ritual for bringing sickness among the [Australian] Arunta. The pointing bone or pointing stick is usually about nine inches in length, pointed at one end, and tipped with a lump of resin at the other. The stick is endowed with magical power by being 'sung over,' that is, curses are muttered over it, such as 'may your heart be rent asunder' and 'may your head and throat be split open.' On the evening of the day on which the bone has been 'sung' the wizard creeps stealthily in the shadows until he can see the victim's face clearly by the firelight. He then points the bone in the victim's direction and utters in a low tone the curses with which the stick was endowed earlier in the day. The victim is supposed to sicken and die within a month at the most. Two men may cooperate in the pointing operation. Spears may also be endowed with magic by 'singing' over them. A person who knows that he has been injured, even slightly, with a spear thus prepared will be likely to waste away through fear unless counter magic can be brought to his aid.
--from "Primitive Theories of Disease" by Spencer L. Rogers in Ciba Symposia (April 1942)
Sir James Frazer's Golden Bough (1922) is full of curious information -- including his description of a very strange occupation, the spittle burier:
In the Sandwich Islands chiefs were attended by a confidential servant bearing a portable spittoon, and the deposit was carefully buried every morning to put it out of the reach of sorcerers. On the Slave Coast, for the same reason, whenever a king or chief expectorates, the saliva is scrupulously gathered up and hidden or buried. The same precautions are taken for the same reason with the spittle of the chief of Tabali in Southern Nigeria.
Even though the guy was burying spittle, he probably thought he was doing a pretty important job. And in his culture, perhaps he was.
The portrait below shows Kaneena, a chief of the Sandwich Islands in the late eighteenth century, whose spittle would presumably have been buried.
If you're ever at a dinner party where the host has a set of forks that look like these, you might want to consider leaving, quickly.
These are Fijian "cannibal forks" used for eating human flesh. The iron dance blog offers this description of them:
The cannibal fork, or iculanibokola, was used by attendants during ritual feasts to feed individuals considered too holy to touch food. These forks arose for several reasons. First is a cultural taboo that prohibits chiefs and priests from touching food with their hands. Common Fijians generally did not use utensils until Europeanization. One of the most important ceremonies a chieftain participated in was the devouring of their or the tribes enemy. Combining the significance of the event and the inability to use their hands the chiefs needed a way to participate-hence the development of the cannibal fork. Forks became a way to show power and influence. The fancier more elaborate the fork, the higher status the owner had.
Fijian cannibal forks are still made, to sell to tourists. What the tourists use them for... I guess that's their own business.