When people hear about my 16 month long odyssey of hunting and fishing for edible invasive species around North America for my upcoming book, 'Eating Aliens,' I often hear a spiel about how 'human beings are the most invasive species!'There is no question that human beings have spread all over the globe and transformed habitat as we have expanded. However, I do not agree with the idea that human beings should be considered an invasive species in North America.
The conventional view in academia of human colonization in North America puts the initial migration from Asia over land that is now underneath the Bering Sea about 13,000 years ago. This is referred to as the 'Clovis Culture,' and it has been traced largely by looking at stone tools that show a distinctive set of shaping techniques.
There is now a lot of reason to question the single-migration hypothesis. It is very possible that there were multiple waves of migration from different places at different times. Credible scientists are now looking back as far as 21,000 years ago at archeological evidence on the Atlantic coast that suggests a very old migration from Europe (in addition to the migrations from Asia).
With a time line of between 13,000-21,000 years since humans first arrived in North America, this begs the question of exactly how long it takes for us to consider a species to become native. Perhaps a basis of comparison would be useful. Let us consider some other 'native' wildlife in North America.
Elk have only been in North America for around 10,000 years. During an ice age in which sea levels were lower, they crossed over from Asia along the same route that the Clovis humans did. They are so similar to European red deer that until very recently many taxonomists considered elk to be a subspecies of red deer. They interbreed readily.
Mule deer have only existed for about 5,000 years when they evolved rapidly from an isolated population of whitetails that interbred with blacktails.
Either we should consider elk and mule deer to be 'invasive' in North America or human beings should be considered native. We've been here longer than they have.
I have heard a response to this perspective that I do not much care for. On a number of occasions I've heard people say, 'but those were Native Americans and now we have white people, which are invasive.'
Yes, now we have white Europeans in North America. Also Africans, Chinese, Japanese, and other human beings from all over the world. If you are going to make an argument that these people are invasive and the other ones are not, this requires a belief that different races of humans constitute different species. This idea falls apart easily under scientific scrutiny, and aside from the science it opens the doors to all sorts of racism and potentially excuses genocide.
What separates one species from another? Appearance is the easiest thing for us to point to. But appearance isn't the most important factor. This is actually a huge, sprawling issue that I cannot settle in the course of only a few paragraphs. This article on Stanford's website is a good place to start if you are interested in this sort of thing.
I won't pretend that this is the whole of a definition of 'species' (among other things because what I am about to say would ignore the reality of asexual reproduction) but I believe that it is correct to say that you are definitely dealing with a single species if you have two organisms that are:
1. In practice, in the wild, willing and able to interbreed of their own volition;
2. Able to consistently produce offspring that are both fertile and able to survive and mature in the wild.
A lot of physical and behavioral variation is indirectly addressed through the second criteria. For example, mule deer and whitetails are willing to interbreed and they produce fertile offspring, but few of those fawns survive to maturity. The hybrids try to run uphill from danger like a mule deer, but their gait is badly suited for this without the advanced tendon structure of a full-blooded mule deer. They get sorted out of the gene pool pretty quickly.
A combination such as, say, a Vietnamese woman and a European man look very different. But we have yet to find a combination of human races which are unwilling to interbreed after a few drinks. Nor has medical science found a pairing of races that results in sterile offspring, or in children that have functional disabilities like that of the hybrid deer which prevent them from surviving to maturity. In functional evolutionary terms, the settlers at Jamestown were of the same species as the Powhatans that they met in Virginia.
Homo sapiens sapiens is native to North America. We've been here a good long time. That doesn't mean that we're doing a good job of looking after our native habitat, and of course there are other places in the world where a good case could be made for calling us 'invasive.'
[Photo copyright 2012 by Jackson Landers.]
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