08/11/2014 04:51 pm ET Updated Oct 11, 2014

Alien Species: Not All Bad, and Not Even All Alien

Dean Fikar via Getty Images

North America has beavers. Europe and Asia have beavers. Britain should have them too, but we killed the last one a few centuries ago. But now they have turned up on a river in southern England, happily doing what beavers do, including having baby beavers.

No one knows how they got there. The official reaction is that they must be captured and put in a zoo, because "[o]ur landscape and habitats have changed since then and we need to assess the impact they could have." In fact, we know beavers are, on balance, a Good Thing, increasing biodiversity and reducing flooding. And beavers aren't an isolated case; the UK government is in the middle of trying to change the law to officially classify all extinct British species as aliens and thus subject to potential "eradication or control."

Why governments -- anywhere -- do what they do is usually opaque to me. I assume some calculation of electoral advantage is often involved, but I suspect a desire for a quiet life also enters into it. If all species "not ordinarily resident" in the UK, even former natives, are outlaws, then at least officials don't need to struggle to invent excuses to capture, shoot or poison any specific example. The answer is always no, because that's what the law says.

I've been a university ecologist all my life, and in common with the overwhelming majority of the ecological/conservation community, I started out disliking alien species as a matter of principle. But that dislike is based on aliens not "belonging," and the whole idea of belonging is based on not much at all. I called my book "Where Do Camels Belong?" (see brief extract below) because camels are a neat example of an animal where "belonging" is particularly hard to pin down. At the opposite end of the UK, in Scotland, there are officially sanctioned reintroduced beavers. Apparently they do belong, unlike their southern cousins, because we put them there.

In short, if we go around pretending that we know where everything should be and acting like self-appointed policemen to make sure they stay there, we will waste an awful lot of time and money on lost causes, we may not pay enough attention to the few species that really do need controlling, and we may even harm the ability of the natural world to adjust to climate change, habitat loss and other human impacts.

Pretending that all aliens are bad, that all natives are good, and that origin is a shortcut to value will get us nowhere. If we think we have reason to dislike a species -- native or alien -- we should first check if it is actually causing net harm, and specifically if the species itself is the problem and not merely a symptom of some other problem. We should not define the "costs" of aliens in a circular, question-begging way, such that alien species are harmful by definition. We should be reasonably confident that the benefits of control will outweigh the costs, bearing in mind that those costs may extend indefinitely into the future. Last but not least, we should stop imagining that persecuting aliens is some kind of moral imperative.

Below is an extract from the introduction to Where Do Camels Belong?:

Where do camels belong? Ask the question and you may instinctively think of the Middle East, picturing a one-humped dromedary, some sand and perhaps a pyramid or two in the background. Or if you know your camels and imagined a two-humped Bactrian, you might plump for India and central Asia. But things aren't quite so simple if we're talking about the entire camel family. Camelids (the camel family) evolved in North America about 40 million years ago. Titanotylopus, the largest camel that has ever lived, stood 3.5 m high at the shoulder and ranged through Texas, Kansas, Nebraska and Arizona for around 10 million years. Other species evolved very long necks and probably browsed on trees and tall shrubs, rather as giraffes do today. Much, much later camels spread to South America, and to Asia via the Bering Strait, which has been dry land at various times during the recent Pleistocene glaciations. Camels continued to inhabit North America until very recently, the last ones going extinct only about 8,000 years ago. Their modern Asian descendants are the dromedary of north Africa and south-west Asia and the Bactrian camel of central Asia. Their South American descendants are the closely related llamas, alpacas, guanacos and vicuñas (llamas are only camels without humps; all you need to do is look one in the eye for this to be pretty obvious). Now you know all that, let me ask you again: where do camels belong? Is it:

(a) in the first place you think of when you hear the word 'camel', i.e. the Middle East.

(b) in North America, where they first evolved, lived for tens of millions of years, achieved their greatest diversity, and where they became extinct only recently.

(c) in South America, where they retain their greatest diversity.

Or, just to muddy the waters a bit more, is it:

(d) in Australia, where the world's only truly wild (as opposed to domesticated) dromedaries now occur.

Finally, if you felt able to give a confident answer, can you explain why?

If you think camels belong where they evolved, the question has only one answer: North America. If it means where they have been present for the longest time, the answer is the same. If it means where camels have been present during recent millennia, then the answer is Asia and South America. If camels belong wherever they can thrive without human assistance, then it must also include Australia. These are all perfectly reasonable interpretations of belonging.

And there is nothing particularly special about camels. Dispersal over huge distances is not at all unusual among land animals, and it is almost routine among birds. Horses are much the same as camels, and frogs, toads, shrews, deer, cats, weasels, otters, hares, skinks, chameleons and geckos are among the many other groups that now occur almost everywhere, and do so as a result of relatively recent dispersal -- without human assistance -- often starting out in Africa or south-east Asia. None of these species have an obvious answer to the question about where they belong -- whether they are natives or aliens -- any more than camels. Indeed, once you adopt a view of the world that doesn't assume that there's something very special about where things happen to be right now (or in relatively recent history), asking where anything belongs tends not to have an obvious answer.