Humans tend to be really weird about biology. We study other animals and explain their behaviors through the laws of ecology, but then very quickly make exceptions for ourselves. We accept the theory of evolution through natural selection but then twist ourselves in knots explaining how “modern” humans have somehow stopped evolving.
Similar logic applies to human behavior. We are in no way immune to the theories of behavioral ecology that drive all animal behavior. Yet, because of our abnormally large brains we say that humans are a special case. We say things like “but humans have free will” and “but humans have the power of logic and reason” to explain why humans aren’t compelled by biological forces.
Of course, we can’t excuse socially unacceptable behaviors as purely acting on biological instinct. We expect humans to know better because we form societies that establish rules. We expect people to recognize those biological impulses but not always act on them. However, many of those impulses are so subtle that we don’t even recognize them at the time as the driving forces behind our behavior.
Dispersal is one such phenomenon. Biologically, dispersal (not migration) is the impulse that drives individuals of a species to leave their place of birth and move to a different place for mating. This can be similar to migration, but dispersal is usually a one-way street, whereas migration is usually a round trip. Think of birds flying south in winter and north in summer. That’s migration. But an individual bird that leaves the family nest and establishes a new territory a few kilometers away from its parents’ territory is dispersing, not migrating.
The drive to disperse is pretty basic. It boils down to risk vs. reward. The penalty for not dispersing can be mating with a partner who is too closely related, thus risking inbreeding and all the complications that come with that. The risk can also include resource competition with siblings or parents. Think of two lion brothers fighting to take over the pride of their father, but the matriarch of the pride is their mother, and it includes many of their aunts and sisters. Biologically, there is little good that can come of this. But if those males leave the area, to “light out for the territory” as Huck Finn said, and find mates in an unrelated pride, they can spread their genes much further, producing offspring with more heterozygosity (just trust me that this is a good thing), and stand a much better chance at surviving long enough to produce viable offspring who will then survive long enough to produce their own viable offspring, rinse and repeat. This, by the way, is the very definition of biological fitness. “Survival of the fittest” literally refers to biological fitness (producing viable offspring), not the physical fitness of the individual.
Dispersal is not without risk, however. There’s a chance that those dispersing young males might not find any females to hook up with. They may not even find suitable habitat at all, wandering in the desert until they collapse and die. They may be killed along the way by other territorial males. They may encounter all manner of threats and challenges that prevent them from establishing a territory and mating. If they make it, the reward is potentially huge. But if they don’t, then they’ve gambled and lost.
Does any of this sound at all familiar when applied to humans? Think of any number of examples from history of adventurous young men “lighting out for the territory” into the unknown, at great personal risk, seeking huge personal reward. The vast majority of whom never returned “home” but established new homes in a far in and distant land. That trait was the defining feature of the age of exploration. It drove guys like Marco Polo to trek halfway across the world on the Silk Road. Think of the gene flow that such a road opened up for humans between Europe and Asia. Marco might have been driven for a desire for riches and adventure, but without question he almost certainly spread his Italian genes halfway around the world in the process.
Think of other examples like the California or Yukon gold rushes. By and large, these were examples of young men dispersing to seek the reward of a quick fortune in a distant land. And if you think the desire to amass a fortune is unrelated to the drive to find a mate, you’re really fooling yourself that humans are immune to biological drivers. I ain’t sayin she’s a gold digger, but…having a big sack of nuggets certainly doesn’t hurt your chances of producing offspring.
Very few human populations have ever had long-term problems with inbreeding and lack of gene flow, as humans have always been driven by a very strong urge to disperse. As a species we don’t tend to sit still for long. Populations that get cut off and isolated tend to be visited eventually by some random Marco Polo type who pops in and sows some wild oats, introducing new genes into the pool.
In any species, dispersal is an individual-level drive. Again, think of this as one of the differences between migration (populations) and dispersal (individuals). Within any population or group, some members will never disperse. They’re perfectly happy to take their chances marrying Becky Sue, whom they’ve known since kindergarten. (We all know those couples who look like they could be siblings. Genetically, they’re not far from it). They weigh the risks and rewards and decide to take their chances with the devil they know. Inbreeding be damned, me and Becky Sue are in love, goldammit, and I don’t care if she is my first cousin! And this works out okay, for the most part, because those who do light out for the territory help ensure that the larger population’s gene pool doesn’t start to stagnate from the likes of Billy Ray and Becky Sue from Homozygote City.
We are often tempted to think that the urge to get the hell out of Dodge is driven by some sort of childhood trauma. Sure, some people strike out to escape terrible situations, but many come from perfectly happy homes with loving families. In fact, nurturing parents who encourage exploration, critical thinking and risk-taking might ignite that innate dispersal drive that might otherwise not have been activated.
Personally, I’ve always been the type whose feet were perpetually itchy. I left the nest by age 18 and never really came back for any extended period. I now live around 8,500 miles from my place of birth. My leaving home was not in any way a desire to get away from a bad situation. It was more of a feeling that the world I grew up in was not big enough for me. I had to see what was out there, to know for myself what lay beyond the horizon. My parents always encouraged me to find my own path and didn’t attempt to rein me in, which I appreciate enormously. I have never been driven by a desire for gold or adventure, but I guess my biological dispersal drive was strong.
I think humans would be better off as a species if we recognized the role that biological drivers play in our everyday lives. Humans are animals, remember. We are primates in the class Mammalia, just like gorillas, chimps, and the slow loris (she’s cute, but she’s kinda slow). I’ve heard it said that if an alien scientist were to land on earth it would probably be tempted to classify humans and chimpanzees as the same species, or at least members of the same genus. We do have around 98% of our genes in common, after all. So why would we ever think that the biological theories that explain the behavior of a slow loris wouldn’t also apply to us?