You may be wondering how any of this might apply to islands, or how species travel from mainland to island might be similar to how some non-native species travel now, which is often in the bilge water of cargo of ships. I admit, those two comparisons do have their similarities. There is no slow migration across land bridges onto islands. Well, that’s not true, that was possible for some islands like I mentioned with Adam’s bridge, and likely possible for at least some of the Oceania islands, such as those that make up the Philippians and Indonesia. But with many of the others, such as the Galapagos, chances are that’s not what happened.
In my post Island Isolation Aids Evolution I discussed a bit about how species arrive at islands. Just as a quick re-cap, some of these methods involve birds flying to these newly exposed sites (newly exposed as water levels drop or the islands themselves rise, or newly created by volcanoes) for a rest, dropping seeds and tiny species as they land. Some species such as reptiles may be able to survive on floating vegetation and wash up on shore, while others can just swim. Once some vegetation springs up, migratory birds might be more likely to increase their frequency of visitation, and other birds can get blown off course in storms, sending them from their continental homes and to the direction of islands.
These arrivals weren’t quite the slow progression found on the mainland (though, this same thing can happen to the shores of continents as well), they were rather abrupt. However, they were also probably pretty rare, and when it did happen, the number of individuals to arrive were very low. Also, you’re not going to find a species from the middle of Russia floating on vegetation to arrive on some tropical island, either. Any animal that swam, flew, or floated to an island probably did so from one of the closer landmasses, and as such, their climate and perhaps even some of the species in both places would be relatively similar.
This isn’t to say species that were there first wouldn’t be overrun and outcompeted by these newbies, but their arrival wasn’t determined by humans, either. Perhaps it’s just my opinion (and it’s my blog, after all), but whether or not a species was purposefully introduced by humans (“an act of short-sighted ecological vandalism”, to quote the author of the NY Times article) or accidently introduced by carelessness, doesn’t equal the same level of introduction as more independent migration. I mentioned some of the harm invasive species can have on their new homes here: Threats to Ecosystems
Of course, there are some species that are so common place now that most people think they are actually native to certain areas when they are not. The house sparrow (Passer domesticus) is native to Eurasia but can be found in many parts of the Americas and are common there. How’d they get here? Europeans brought them over. They also distributed them to parts of southern African, Australia, and New Zealand. There are many more, but I offer this common bird as an example. What you think is native may actually not be!
Back to the migrations, this land travel across bridges is how Native Americans came to the America, how Europeans arrived in Europe, how Asians arrived in Asia. It, of course, is not how Europeans came to the Americas or Africa or Australia. What makes someone American or European has become jumbled up now. I was born in the United States so I’m automatically considered an American despite my largely European descent, but am I and everyone else a Native American just because we were born in the Americas? No, I’d have to say, we are not.
The first humans arrived in the Americas around 14,000 to 12,000 years ago. There was more than one migration, but these were the earliest people. The skin tone of Native Americans and other general structural features are different from that of their Asian origin (there is a fairly new hypothesis that a European group may have reached the Americas before and perhaps instead of, Asians) just as Asian features are different from their Middle Eastern and before that, African features. Within this chunk of thousands of years, humans adapted to their new homes. Skin color is a result of melanin in the skin, which, through the process of evolution by natural selection, adapts to the climate and sun exposure levels over thousands of years.
The point is, Native Americans have adapted to the Americas. These adaptations would have been different if they were located somewhere else, and non-existent if they hadn’t been in the Americas for quite a while. While their initial arrival may have upset the then-current ecological balance, the small and slow migration down through the Americas gave species and ecosystems time to adapt if they could. It wasn’t sudden. That sounds native enough for me.
Yet, genetically there is virtually no difference between ethnicities, we are all just Homo sapiens. So, as long as Native Americans are classified as native, shouldn’t humans in general? I don’t really have an answer for that. Those of European descent are obviously still adapted, even now, to a European climate, not an American one, yet these differences are really only skin deep at best. What I do believe though, is that the culture, brought over by Europeans is not native. It didn’t originate here. It didn’t slowly evolve and adapt as most tribal cultures have, to the land and species. It was thrown in rather suddenly, spread quickly, adapted as needed though I’d argue not fundamentally but only superficially, and basically crushed anything that stood in its way. An evolution of culture could make the invasiveness of the culture, and the humans, decrease. Humans can be invasive, but they don’t have to be. There is a choice there. One the nutria didn’t have.