Says who? We didn't all benefit equally from the domestication of cows. Some people are lactose intolerant. I really don't understand this obsession with equality that is unheard of in nature. It's completely subjective. Equality in outcomes or equality in opportunity? Equal rewards for effort or for productivity? The former produce what economists call "perverse incentives". http://en.wikipedia.org/wiki/Perverse_incentive

You really should read this: http://www.tnellen.com/cybereng/harrison.html