“Most kinds of aggressive behavior among members of the same species are responsive to crowding in the environment.”
On Human Nature (1978), Ch.5 Aggression
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Edward O. Wilson 83
American biologist 1929Related quotes
Axelrod, Robert, and William Donald Hamilton. "The evolution of cooperation." Science 211.4489 (1981): 1390

Ai Weiwei on Twitter in English (beta). http://aiwwenglish.tumblr.com/ (January 10, 2011)
2010-, Twitter feeds, 2010-12

Males pursue, show off, brawl, scuffle, and make general fools of themselves for love. A major failing of most feminist ideology is its dumb, ungenerous stereotyping of men as tyrants and abusers, when in fact — as I know full well from my own mortifying lesbian experience — men are tormented by women’s flirtatiousness and hemming and hawing, their manipulations and changeableness, their humiliating rejections. Cock teasing is a universal reality. It is part of women’s merciless testing and cold-eyed comparison shopping for potential mates. Men will do anything to win the favor of women.
Source: Vamps and Tramps (1994), "No Law in the Arena: A Pagan Theory of Sexuality", p. 35
Source: Images of Organization (1986), p. 39; As cited in as Vivien Martin -(2003) Leading change in health and social care. p. 157: About the organization as organism.
“Defiance is the reaction against activity (aggression) of the environment.”
Sadism and Masochism : The Psychology of Hatred and Cruelty, Vol. 1 (1939), p. 46
Context: An intense, unyielding stubbornness hides beneath an apparent obedience (the patient brings a vast number of dreams; his associations become endless; he produces an inexhaustible number of recollections, which seem to him very important but are actually of little moment; or he goes off upon some byroad suggested by the analyst and leads the latter into a blind alley).
The child manifests the same reactions of defiance and obedience. The child, too, can hide his stubbornness behind an excessive docility (the parent's command: You must be industrious. Industry may become a mania so that the child neither goes out nor has time to sleep). Obedience is the giving up of the resistance; obstinacy the setting up of fresh resistances. This resistance is externally active. We have in recent years had sufficient opportunity to observe the law of resistance (the passive resistance). Activity and defiance show great differences. Defiance is the reaction against activity (aggression) of the environment. It may then manifest itself actively or passively and stands in the service of the defensive tendency of the ego. Every resistance reveals the ego (one's own) in conflict with another.

Peter Singer - The Genius of Darwin: The Uncut Interviews - Richard Dawkins https://www.youtube.com/watch?v=GYYNY2oKVWU, 2009.
Source: Practical Ethics
Context: Speciesism is an attitude of prejudice towards beings because they're not members of our species, so just as racism means that you're prejudiced against beings who are not members of your race and sexism means you're prejudiced against people of the other sex. So we humans tend to be speciesist in we think that any being that is a member of the species homo sapien just automatically has a higher moral status and is more important than any being that is a member of any other species, irrespective of the actual characteristics of those beings.