Posted by: salamandercandy | May 31, 2007

When the basal devour the derived

While the angels, all pallid and wan, / Uprising, unveiling, affirm / That the play is the tragedy, “Man,” / And its hero, the Conqueror Worm.
-Edgar Allan Poe

In the lay-evolutionist’s mind, the phylogenetic tree of life is often confused with the idea of a “great chain of being:” that living things occur in a series from “least evolved” to “most evolved,” with bacteria at the bottom and humans at the top. The chain of being is further mixed up with the food chain, such that “primitive” species are lower on the food chain, and “advanced” species are higher up the food chain, with humans again on the top. In reality, however, evolutionary relationships form a branching tree pattern, with all extant species on the tips of the terminal twigs, although some lineages have changed morphologically over time more than others, and humans are arguably the most different from the ancient common ancestor to all life. But what about this food chain business? The food chain and the tree of life are different metaphors explaining different relationship patterns, one ecological and the other evolutionary. But are they connected? Within the tree, are species that are more closely related to humans higher on the food chain?

In general, the truth of this trend is obvious; after all, most instances of heterotrophy involve animals eating plants. Similarly, think of all the examples of vertebrates eating invertebrates, amniotic vertebrates eating non-amniotic vertebrates, and humans eating other mammals. All of these acts of carnivory happen much more often than the reverse arrangement. But there are exceptions. Some plants eat animals; dragonfly nymphs eat tadpoles; spiders eat birds; squids eat fish; cane toads eat mice; and certain sharks and crocodiles will eat just about any mammal they can swallow, including humans. And even though ecologists like to separate decomposers and pathogens from herbivores and carnivores, that doesn’t change the fact that we will all eventually be “eaten” by tiny brainless microbes.

For some reason, the thought of a “primitive” creature eating a more “advanced” one appeals to me. It helps explode the myth that there is a consistent chain of command starting with humans and spreading to more distant and lowly portions of the tree. It makes the world appear less one-sided; when a Venus fly trap snaps up its prey, it seems to be striking a blow for justice against the near-totalitarian assault on plants by herbivorous insects. As a vegetarian, I am happy to occupy a lower trophic level than many other animals, and I like evidence that humans are not necessarily meant to be at the top of the food chain. Mostly, though, it humbles our species, and goodness knows we need it. While we claim to rule the world, who was just bitten by a mosquito?

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Responses

  1. the photo you name as a dragonfly nymph eating a tadpole is actually a Giant Predacious Diving Beetle larvae. just thought you might want to know.

  2. Thanks, ginger. I’m not an entomologist, as you can tell. It’s labeled as a dragonfly on the original website. And dragonfly larvae DO eat amphibian larvae, even if I don’t have a picture of it.
    -Jacob


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