Alternate Theories of Human Expansion

At some point in my education I was taught that humans migrated to the Americas 13,000 years ago over a land bridge exposed by lower sea levels during the last ice age. Sea water was trapped in massive glaciers, exposing the Bering Strait. These humans then migrated south at an alarming pace through an ice free inland corridor. Within a few thousand years humans migrated from the tip of Alaska to the tip of South America. This is the prevailing theory to this day amongst mainstream archaeologists. I don’t disagree with mainstream science but I recognize it for what it is; our best current understanding based on the evidence we have. Therein lies the exciting possibility that our current understanding isn’t the entire picture, and could even (gasp) be fundamentally incorrect. Throughout history mainstream scientific theories are constantly proven wrong. However, it takes a great deal of evidence and a very long time to shift mainstream scientific thought. Oftentimes new theories that challenge the mainstream are met with severe scrutiny and hostility. Regardless of if they derive from legitimate scientific methods. One could argue this actually stifles scientific discovery. In order to ascertain a PhD it may not be in your best interest for your thesis to contradict mainstream science that your soon to be peers have based their careers on. The most obvious example of this is Galileo’s excommunication, but I think we should explore a more modern example further past the scientific revolution. In the late 1800s Ludwig Boltzmann contributed significantly to the thermodynamics of gasses based on the existence of atoms. Mainstream physicists at the time didn’t believe in atoms. They refused to let Boltzmann refer to them as anything other than “convenient theoretical constructs”. He even tried to develop a compromise theory such that atomists and anti-atomists could work without arguing over atoms. In 1904 he attended a physics conference in St. Louis and wasn’t invited to the physics section. It is said that this contributed to his eventual suicide some two years later. Of course, a couple years after his death it was found by physicists that atoms do in fact exist. Interestingly, this exact phenomenon is happening right now with the theories surrounding human expansion. Based on DNA evidence evolutionary geneticists now largely believe that humans lived in the Americas up to 20,000 years ago. Additionally, archeological sites have been discovered that date back to 15,000 years. Despite this, many archaeologists refuse to relinquish their belief in the migration dating back to 13,000 years. As an outsider, the possibility that we are wrong, and that there are still things that we haven’t discovered or don’t fully understand makes science exciting. I have a few theories of my own that I find fun to entertain and contemplate. The first is largely centered around the mass extinction of large mammals that coincides with the 13,000 year old human expansion theory. The current theory, expressed with confidence in massively influential books such as Sapiens, Guns, Germs, and Steel, etc. is that this extinction was the result of overhunting by humans migrating into the americas. This is a rather self loathing theory that I believed in strongly until fairly recently. I believe that there are various other plausible explanations that deserve consideration. The first, is that this extinction was mostly caused by the rapid climate change that occurred at that time. This coincides with our updated ideas of when humans made it to the americas, and when these extinctions occurred. If humans did make it into the Americas around 20,000 years ago, and the extinction of large mammals occurred around 13,000 years ago those timelines simply don’t align. The extinction more strongly aligns with rapid climate change. This theory is entertained by many people other than myself. The second, (and more exciting theory for me since I haven’t heard it expressed by anyone other than myself), is this - humans didn’t cause the extinction of large mammals, the void left by the extinction of large mammals is what allowed humans to expand so rapidly. This pattern occurs consistently throughout history. In fact, humans would not be here if it weren’t for this pattern of extinction paving the way for the proliferation of various other lifeforms. One of the more relevant examples of this for humans is the Cretaceous extinction event. This extinction event was the end of 75% or more of the species on earth and the end of the reign of the dinosaurs. This paved the way for the proliferation of large mammals and eventually humans. Had this extinction event never occurred, dinosaurs would still rule the world, large mammals would have never come to dominate, and humans would not be here. I think it’s possible that this is what happened on a smaller scale with humans and large mammals in North America. Another even more radical theory is that humans were in the Americas significantly longer than we believe (50,000, maybe even 100,000 years ago). Sea levels have risen 100 meters since the last ice age ended 13,000 years ago. If humans did live in the Americas at this time they would have lived along coastlines that are now underwater. So, it makes sense that the vast majority of archeological evidence that we’ve found in the Americas is dated to after 13,000 years ago. Perhaps what we previously believed was an extremely rapid migration down the coast, was actually a migration to higher elevations as sea levels rose. This would explain how archaeological evidence of humans appears extremely suddenly and all up and down the coast of the Americas. At the end of the day, it’s impossible for us to know with 100% certainty what exactly happened in human prehistory. I believe all of these theories have some possibility of at least being partially true. Which, as an outsider, is what makes it so interesting and exciting. The real challenge for the scientific community today is how to align incentives such that we maximize human progress. I know one thing for certain; suggesting alternate theories shouldn’t harm the career of a scientist simply because it contradicts mainstream theory. This will stifle scientific discovery and human progress. Thanks for reading, Zach