I would like Twitter to put some kind of filters in place, suggests Prakash. At present I can't see troll tweets if I block the user, but others who go into my 'mentions' can do so, and read the graphic abuse, which is disturbing.

In the 1950s, farmers in Dongsizhuang Village in the city of Yanshi started using a rubber ball to control the water outlet of the underground earthenware waterway.

At various times since Homo first appeared in Africa, it shared the continent with more robust hominids, perhaps several different species of them. … They seem to have evolved from more ‘gracile’ apes (gracile being the opposite of robust). The gracile apes are also placed in the genus Australopithecus, and we too almost certainly emerged from among gracile australopithecine ranks.

As previously noted, the motivational and satisfactional value of a reward system is a function of the perceived equity of the reward system.