A notable result was a change to other-regarding behaviour with age: younger children (3–4 years old) were mostly self-centred, whereas the older children (7–8 years old) were concerned with equality — within their group, that is. Interestingly, this developmental pattern is different from that of another form of altruism, namely 'instrumental helping'. Human infants as young as 14–18 months readily help others do such things as fetch or stack objects, or open cabinets7. For this kind of helping there is direct evidence that infants are not influenced by external rewards, and indeed our nearest primate relatives sometimes help others achieve their goals as well7, 8. So, in the case of instrumental helping, the developmental trajectory is of early altruism and other-regarding preferences, and then, presumably, growing concern with reciprocity and reputation as children learn to be selective altruists so as to avoid being exploited by others.
Can we draw parallels to software licenses? Proprietary is 3 years old. BSD is 8 years old: you share alike and do not expect reciprocity. Cynicism kicks in at puberty, pure altruism is but a distant memory of candy and enter the GPL?