Ever since the earliest cave-dwelling humans wandered in search of safe and supportive lands where they could live and feed their families, a rude awakening would sometimes greet them in the form of another clan, showing up at the same cave, at the same time, when there wasn’t enough room to accommodate everyone.The more similar the two groups looked, smelled and behaved, the better the chances that they would cooperate to share the resources they had found. Human nature leads us to fear those who are different, while we gravitate towards those who are familiar, whether in appearance or in ...