Human Migration and Evolution

Migration has, through human prehistory, both spurred and slowed human evolution. Prehistoric humans were hunter-gatherers. Contingent on the local flora for something approaching seventy percent of their total calories, they hunted for the leftover thirty percent.

Fauna migrate as least as well as humans do, but flora is tied to their environment. The 3 determinants of floral population are mean temperature, available moisture, and distance from the equator. Mean temperature is a consequence of elevation – the higher a place, the less warm, and the inverse tends also to be true. Even the most basic gardener knows that some plants can and others can’t withstand freezing temperatures. Available moisture is self-explanatory.

In the garden, some plants endure benign neglect and others don’t. In nature, some grow close to streams and streams which don’t dry up, needing water, and others can thrive with water only in the decline and spring. The surprising factor here is the distance from the equator, which interprets into how much available daylight falls onto an area, and at what angle. We know due to experience that the sun feels hotter on our skins when it is firmly overhead than when it rises or sets. And earth’s axial lean of 23.5 degrees means more sun falls on the northerly hemisphere in the time we northern-hemisphere dwellers call summer, less in the time we call winter. The situation daylight varies as well with longitude, that is, the distance from the equator : north to south. The equatorial areas have a supply of daylight which varies little round the year, but the further you wander from the equator, the less event daylight is available. The provision of daylight is almost unceasing across bands of latitude, east to west. What this suggests to human migration is if travel happens east to west, migration is pretty much less demanding than travel north to south. Each 30 miles of north-to-south travel, the local flora changes absolutely.

In 30 miles of east-to-west travel, nearly no changes will have taken place in the local flora. Those changes which have taken place will be gentle : a traveling band of humans will be in a position to foretell what flora will be eatable by its similarity to flora they picked up earlier in their journey. North-south travelers will need to conduct a sequence of careful experiments to arrive at understanding of the local eatable plants each 30 miles. Thru human evolution, 30 miles north or south was a generation’s migration. That distance could more than double across the easier east-west routes. Human culture, and at last civilization, must wait upon the creation of survival.

Therefore we see that migration, with its big benefits to east-west travel, shaped us virtually from the start. To people who would travel north-south came difficulty after difficulty, maybe shaping the nascent brain of the first problem-solvers faster than people who went east-west. This east-west group had an advantage of a semi-stable food source which let them reproduce quicker, spreading any evolutionary change quicker thru the gene pool. So, in two separate ways we are the product of our migrations. Are we there yet?

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