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How many species are there, really?

In “Rewriting the textbooks: Noah’s shrinking ark” (part of a series on stuff in the textbooks that could use an airbrush), Kate Douglas (New Scientist, 23 May 2011) tackles the tangled problem of species, supposedly standing at 30 million, which she describes as “almost certainly a huge overestimate.” So not much is systematic apart from the names.

Last year, Andrew Hamilton at the University of Melbourne, Australia, and his colleagues took all these factors into consideration in a new statistical analysis based on beetle counts in 56 species of tree in Papua New Guinea. They came up with a far lower figure for the arthropods – just 2.5 million species or thereabouts (American Naturalist, DOI: 10.1086/652998). 

Multiply this by three, and you come to a total of fewer than 8 million species. Hamilton goes even lower, arguing that vertebrates and plants have been more thoroughly catalogued than tropical arthropods. “The magic number is 5.5 million,” he says (New Scientist, 12 June 2010, p 4).

Why does it matter? Darwinian evolution depends on speciation, so over-readiness to claim that a new species has evolved inflates the claims for Darwinism. More immediately critical from a public policy perspective, environment legislation typically hinges on issues around the extinction of species – but we need to be sure that the species is distinct enough to go extinct.

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7 Responses to How many species are there, really?

  1. Just for starters, most of the “species” in the cattle family aren’t — as witness the periodic hyperventilation over this or that “species” of wild cattle “on the brink of extinction due to interbreeding with domestic cattle.”

  2. evolutionism seems to require its adherents to turn off their critical faculties.

  3. 3

    Why does it matter? Darwinian evolution depends on speciation, so over-readiness to claim that a new species has evolved inflates the claims for Darwinism.

    With respect, this makes no sense. Evolutionary biology explains speciation, among other things. The absolute number of species involved have little or no bearing on the validity or not of proposed mechanisms.

    Regarding species extinction and public policy, definition of a species need not be central to biodiversity conservation legislation. I forget the North American legislation, but in the EU, groups of organisms can be and are legally protected at subspecies level. People are also recognising the importance of conserving local genotypes, leading to policies aimed at protecting the distinctiveness of local populations, whether formally recognised as variants or not. This flexibility of approach is important, given the difficulties involved in defining a species in the first place.

    Lastly, I’ll note that efforts to conserve subspecific genetic diversity include preserving domestic races and strains of livestock (think Scottish Highland, Kerry, and Texas longhorn cattle) and crops.

  4. Prof FX Gumby-

    “Spciation” is an ambiguously, at best, defined term.

  5. 5

    Regarding extinction, as far as I see it, I would say that the mechanism by which speciation occurs is all important when it comes to preservation (however “speciation” is defined). Darwinism maintains that speciation occurs randomly through mutation, or gene transfer, or whatever, which implies that species are unique and once they are gone they are gone forever. ID, however, might suggest that speciation occurs because life is programmed to do so given certain environmental inputs. If this is the case, then I would expect that, once a species goes extinct, there could be a good chance that that particular species might emerge again from some animal of the same genus, or family (or maybe even phylum?). The whole issue of convergent evolution and rapid speciation causes me to suspect this might be the case. And if this is indeed the case, maybe all our conservation efforts are for no good reason at all (to an extent)? Also, if this is true, I would be interested to see if the dodo or mammoth makes a comeback after a few thousand years.

    I’m not saying that we shouldn’t bother with protecting rhinos, elephants and tigers, but it would certainly help certain people feel better about letting that stupid smelt in California go extinct.

  6. M Holcumbrink at 5, perhaps we could usefully think in terms of preserving ecologies rather than species. For example, where there is lush vegetation, we need deer to eat it. Where there are deer, we need coyotes, so at least some vegetation persists. Where there are coyotes, we need a wolf pack or two to scare the coyotes into abandoning their plans to run the world. Where there are wolves … well, you’ve heard the expression “jealous as a wolf”. Seems they police their own numbers quite a bit that way.

    Now suppose we look at the whole lot together, not separately. If any one went extinct, the system would change very drastically, probably in the direction of reduced biomass.

    On the other hand, if someone is shaking the can for one in particular of 50 000 tropical beetles (one that is thought to be going extinct), I would suggest that the best solution is to grab a bunch of them and make a cottage industry of raising them for zoos, education centres, and private insect hobbyists.

    It’s really a question of which efforts are really preventing a degradation of the ecology and which are simply the same motivation by which we preserve historic buildings. A good motivation, but a different one.

  7. 7

    Denyse,

    European nature conservation is backed by the Habitats Directive, which designates special areas of conservation based on the presence of habitats that are rare and declining in Europe as well as species. I’m not sure how it is in Canada, but I’ve long thought the USA needs a similar system. Using the Endangered Species Act as a crutch often leads to trivialisation of the issue. Jobs vs. owls anyone?

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