Tuesday, June 19, 2012

The deeper we dig

Here’s a popular argument for evolution: the deeper we dig, the simpler the life forms we find. This, in turn, assumes the law of superposition: in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it.

Deeper is older is simpler. Hence, the evolution of life from simple to complex.

I’m not a zoologist or paleontologist, but I find that inference pretty dubious.

i) According to evolution, dinosaurs are older than mammals, but are dinosaurs simpler than mammals? For instance, are Pterosaurs simpler than bats?

ii) From what I’ve read, most fossils are aquatic organisms. So their body plan would be keyed to the nature of their habitat.

iii) Are insects simpler than birds? If so, are insects simpler because they’re more primitive, or because they’re insects? What else would an insect be like–and still be an insect?

iv) I suppose earthworms are simpler than leopards. But the simplicity of an earthworm is related to its function. What does it do compared to what a leopard must do? What’s its distinctive contribution to the ecosystem? Doesn't that account for the difference?

v) I assume there’s a rough correlation between size and complexity. One reason an amoeba is simpler than a cat is because an amoeba is far smaller than a cat. It’s not physically possible for an amoeba to have the complexity of a cat. There's not enough “space.”

Assuming that organisms are simpler the deeper we dig, is that because they are older–or smaller?

vi) It’s often equivocal to say one organism is simpler (or more complex) than other, for the comparison operates at more than one level. An organism may be simpler in one respect, but more complex than another. Take the follow examples (see below). According to evolution, these species are far more “primitive” than humans, yet their senses are far more “advanced” or highly “developed.”

STOMATOPOD crustaceans, commonly named mantis shrimps, have compound eyes of unique design. A central band composed of six parallel rows of ommatidia separates two peripheral ommatidial groups, and all three regions view the same area of visual space1–3. In the central bands of members of the stomatopod superfamily Gonodactyloidea, four of the ommatidial rows are built of tiers of photoreceptors; in two of these rows, the photoreceptors themselves contain coloured filters4. Such a design could in principle produce many spectral classes of photoreceptors using only a single visual pigment4,5. We measured the absorption spectra of the coloured filters and the visual pigments in frozen sections of retinae of a typical species, Pseudosquilla ciliata, using end-on microspectrophotometry. The retina contains not one, but as many as ten visual pigments, each in a distinct photoreceptor class, having maximum absorbances at wavelengths from 400 to 539 nm. Because of the unique anatomy of stomatopod eyes, ten or more spectral types of photoreceptors exist in this species.

Sharks’ electroreception sense is incredibly sensitive. According to Scientific American, sharks can detect electric currents as weak as one-billionth of a volt. Moreover, Discovery News reports that a shark could pick up the change in electrical current if two AA batteries were connected 1,000 miles (1,600 kilometers) apart and one drained out. It probably helps that sharks have plenty of ampullae of Lorenzini -- around 1,500 or so -- to catch those electrical impulses. In fact, shark specialists have theorized that hammerhead sharks are such excellent hunters because their flat faces have more surface area and are therefore riddled with more ampullae.

Scientists recently found that edge detectors in the brain must reconstruct the heat distribution from blurry images to inform the snake of greater detail of its surroundings.

Some snakes have infrared vision. Also called “heat vision,” the infrared rays, which have longer wavelengths than those of visible light, signify the presence of warm-blooded prey in 3 dimensions, which helps snakes aim their attacks. Pit vipers and boids, the two snake types that possess this ability, have heat-sensitive membranes that can detect the difference in temperature between a moving prey—such as a running mouse—and its surroundings on the scale of milliKelvins.

“The information of the infrared and the visual system are both represented in the optic tectum,” Sichert told PhysOrg.com. “This information forms a neuronal map, where, for example, the front part of the optic tectum represents the part of visual space in front of the snake. How exactly the two systems merge is as yet unknown.

In fact, Sichert added that snakes’ heat vision presents such a clear image when reconstructed that it surpasses even many human devices. “The infrared system of snakes is still as good as—and, in fact, far better than—any technical uncooled infrared camera with a similar number of detector cells,” he said.

Compound eyes in living arthropods such as insects are very sensitive to motion, and it is likely that they were similarly important in predator detection in trilobites. It has also been suggested that stereoscopic vision was provided by closely spaced, but separate eyes. Vertebrate lenses (such as our own) can change shape (accommodate) to focus on objects at varying distances. Trilobite eyes, in contrast, had rigid, crystalline lenses, and therefore no accommodation. Instead, an internal doublet structure (two lens layers of different refractive indices acting in combination) corrected for focusing problems that result from rigid lenses. The shapes of some trilobite lenses, in fact, match those derived by optical scientists over 300 million years later to answer similar needs. Compare, for example, the optical designs of the 17th century physicists Descartes and Huygens shown below, with those of two trilobite species. The result is that, even without the benefit of accommodation, the rigid trilobite doublet lens had remarkable depth of field (that is, allowed for objects both near and far to remain in relatively good focus) and minimal spherical aberration (distortion of image).

vii) Finally, here’s a useful discussion:

And so is this: Kurt P. Wise, “The Origin of Life’s Major Groups,” in Moreland (ed.) The Creation Hypothesis, chap. 6.


  1. Great observations - pun intended.

    I would challenge one thing:

    "the deeper we dig, the simpler the life forms we find"

    1. It's been noted for along time that while smaller animals tend to be in the lower strata, there are plenty of complex organisms down there.

    2. Most of the different kinds of organisms found in the lower strata have similar kinds of organisms still reproducing today. (IOW: Why didn't they evolve?)

    3. Even the simplest organisms have the same level of cellular complexity as complex organisms. They have less morphological baggage so their genome is simply smaller, but their cell structures are at least as complex. In fact, they often have greater complexity in some respects because of the need of the cell to fend for itself. The exception would be viruses. However, they have the sophisticated capacity to compromise the defenses of more complex life forms.