Species inflation

Species inflation

Hail Linnaeus
May 17th 2007
From The Economist print edition


Conservationists—and polar bears—should heed the lessons of economics

“NO SCIENCE in the world is more elevated, more necessary and more useful than economics.” That was the view of Carl Linnaeus, a Swedish naturalist, born three centuries ago this week, who is better remembered for devising the system used to this day to classify living organisms.

Linnaeus sought to reveal what he saw as the divine order of the natural world so that it might be exploited for human benefit. He lived at a time when exploration and trade were bringing new specimens to the attention of European scientists. Those specimens, particularly the plants, were scrutinised as potential crops. At the turn of the 17th century there was no sense of how creatures were related to each other; descriptions and classifications were unsystematic. Linnaeus gave life to an organising hierarchy with kingdoms at the top and species at the bottom.

The system he created has proved both robust and flexible. It survived the rise of evolution. It also survived the discovery of whole categories of organism, such as bacteria, that the Swede never suspected existed. But, rather as John Maynard Keynes observed that “there is no subtler, no surer means of overturning the existing basis of society than to debauch the currency,” so Linnaeus's system is being subtly debauched by over-eager taxonomists, trying to help conservation.

Go forth and multiply

As new areas are explored, the number of species naturally increases (see article). For example, the number of species of monkey, ape and lemur gradually increased until the mid-1960s, when it levelled off. In the mid-1980s, however, it started rising again. Today there are twice as many primate species as there were then. That is not because a new wave of primatologists has emerged, pith-helmeted, from the jungle with hitherto unknown specimens. It is because a lot of established subspecies have been reclassified as species.

Perhaps “reclassified” is not quite the right word. “Rebranded” might be closer. Taxonomists do not always get it right first time, of course, and what looked like one species may rightly later be seen as two. But a suspiciously large number of the new species have turned up in the limited group of big, showy animals known somewhat disparagingly as “charismatic megafauna”—in other words the species that the public, as opposed to the experts, care about.

One reason for this taxonomic inflation is that the idea of a species becoming extinct is easy to grasp, and thus easy to make laws about. Subspecies just do not carry as much political clout. The other is that upgrading subspecies into species simultaneously increases the number of rare species (by fragmenting populations) and augments the biodiversity of a piece of habitat and thus its claim for protection.

In the short term, this strategy helps conservationists by intensifying the perceived threat of extinction. In the long term, as every economist knows, inflation brings devaluation. Rarity is not merely determined by the number of individuals in a species, it is also about how unusual that species is. If there are only two species of elephant, African and Indian, losing one matters a lot. Subdivide the African population, as some taxonomists propose, and perceptions of scarcity may shift.

The trouble is that the idea of what defines a species is a lot more slippery than you might think. Since it is changes in DNA that cause species to evolve apart, looking at DNA should be a good way to divide the natural world. However, it depends which bit of DNA you look at. The standard technique says, for example, that polar bears are just brown bears that happen to be white. This is not good news for those relying on the Endangered Species Act. For a certain sort of Colorado rodent (with, alas, a nose for prime riverfront real estate) the question of whether it is “Preble's meadow jumping mouse” or a boring old meadow jumping mouse may be a matter of life or death: local property developers are on the death side. The Bahamas switched overnight from protecting their raccoons to setting up programmes to eradicate them when a look at the genetic evidence showed the animals were common Northern raccoons, not a separate species.

The 21st-century answer to this 18th-century riddle is that a species is what a taxonomist says it is. Evolution often fails to produce the clear divisions that human thought in general, and the law in particular, prefers to work with. It therefore behoves taxonomists to be honest. If they debase their currency, it will ultimately become valueless. Linnaeus the economist would have known that instinctively.


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