Thursday, October 06, 2005

Go to the ant-lion, you Darwinist, consider its ways and be wise! (~Proverbs 6:6)

I was continuing my reading of Pierre Grasse's "Evolution of Living Organisms" (see my previous post, "Pierre Grasse and the `irreducible complexity' of the blood-clotting cascade" for who he was) and I came across his description of the ant-lion (Myrmeleon formicarius, etc.), the larval stage of an otherwise unremarkable lace-winged fly (order Neuroptera).

But first, some background:
"ANT LIONS, name given to the larvae of a group of insects belonging to the Neuroptera and related to the Lacewing flies. The larval Ant lion digs itself a small conical pit in sand or soft soil and buries itself at the bottom of it. Ants and other small insects wandering across the ground fall into the pit and are seized by the Ant lion before they are able to escape up the loose soil of the pit walls. Ant lions, Myrmeleon spp, are common in southern Europe and the family is very widely distributed in tropical and subtropical regions. The adult Ant lion fly bears a superficial resemblance to the thin-bodied dragonflies, from which it is easily distinguished, however, by its long clubbed antennae and two prominent parallel veins in the wings which have no cross veinlets between them. Some of the tropical species may have a wing-span of up to 4 or 5 in (10-12½ cm). Their wings are usually of equal size, translucent with mottled patches. Some tropical species have enormously elongated hindwings drawn out at the ends so that they are shaped roughly like a squash racquet. Ant lions are nocturnal and their weak flight, achieved with their seemingly oversized wings, makes them conspicuous as they fly around lights. The larvae generally have pear-shaped bodies with enormous curved mandibles. Some species in Southeast Asia have a greatly elongated prothorax which gives the impression of a very long neck and therefore a rather bizarre appearance. FAMILY: Mymeleontidae, SUBORDER: Planipennia, ORDER: Neuroptera, CLASS: Insecta, PHYLUM: Arthropoda." (Fisher R.C., "Ant lions," in "Encyclopedia of the Animal World," [1977], Bay Books: Sydney NSW, Vol. 1, 1982, reprint, pp.84-85)

Dawkins mentions the ant-lion briefly in his latest book, "The Ancestor's Tale" (2004), noting that it is unique, i.e. among the "things that have evolved only once", but again [see posts 26-Jul-05, 25-Aug-05 & 07-Sep-05] Dawkins does not explain how RM&NS (the natural selection of random mutations) gradually step-by-tiny-step, micromutation-by-micromutation, produced the ant-lion's unique set of coordinated and interdependent features without which most (if not all) it could not have functioned in that role at all:

"How about things that have evolved only once, or not at all? ... I put the challenge to my Oxford colleague the entomologist and naturalist George McGavin, and he came up with a nice list, but still a short one compared with the list of things that have evolved many times. ... Ant lions are insect larvae of the order Neuroptera. Like many larvae, they look nothing like their adults. With their huge jaws, they could be good casting for a horror film. Each ant lion lurks in sand, just be the surface at the base of a conical pit trap which it digs itself. It digs by flicking sand vigorously outwards from the centre - this causes miniature landslides down the sides of the pit, and the laws of physics do the rest, neatly shaping the cone. Prey, usually ants, fall into the pit and slide down the steep sides into the ant lion's jaws. ... They are sometimes knocked down into the pit by the particles of sand." (Dawkins R., "The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution," Houghton Mifflin Co: Boston MA, 2004, pp.592-593)

Grasse starts with a general point: "The humblest creature often poses evolutionary problems ... that cannot be escaped by mere rhetoric"! He then lists the "exceedingly rich collection of coaptations" (i.e. "complementary morphological features that allow close interlocking of opposing surfaces") that enable the ant-lion to live its unique way of life (numbered by me in square brackets):

"COAPTATION AND ADAPTATION OF UNLIKE PARTS. The humblest creature often poses evolutionary problems in stark terms that cannot be escaped by mere rhetoric. None is more `antichance' than the ant lion larva, for it offers the naturalist an exceedingly rich collection of coaptations and in all its organs pushes specialization, both morphological and physiological, to an extreme. Its [1] head is flat and [2] its mouth has become a slit hermetically closed by a double lock, two astonishing coaptations of parts formed independently of one another during ontogeny. The forward edge of the head is bent back underneath to form the upper lip, while a hexagonal plate whose real edge is welded to the wall of the skull forms the lower. The roof of the buccal slit has a triangular projection that fits into a preexisting hollow of the lower lip, the whole forming a kind of pushbutton. A second, complementary locking device is a dovetail assembly in which a sideways and forward projection of the floor of the pharynx is lodged in a corresponding groove in the roof of the mouth. A closed mouth is admittedly not conducive to absorption of food, and rules out all solids, but the ant-lion larva has adopted a very special means of nourishment: It pumps out the body fluids of its victims. Because of the locking of the buccal orifice, [2] the mandibles and maxillae are pushed laterally rearward from the oral cavity to the edges of the slot. They are highly elongated and their free extremities curve inward to form sharp-edged pincers. The mandibles have a [3] longitudinal groove on their inner face running as far as the root of the appendix, thus communicating with the buccal cavity. The maxilla, reproducing on a smaller scale the curve of the mandible, runs parallel to its inner side; externally it has [4] a gutter, which fits extremely snugly to the groove in the mandible. The superimposed trench and gutter form, edge to edge, a capillary channel: Coaptation is perfect. The ant lion larva ... digs its buccal pincers into the body of its prey. It first injects [5] a paralyzing poison secreted by a gland and kept ready in a small basilar swelling of the maxilla; the poison travels not down the capillary channel but along a longitudinal gap between epidermis and cuticle; thus, it does not mingle with the digestive juices. Once the prey is paralyzed, the ant lion injects into it, via its maxillomandibular capillary tube, digestive juices that attack and liquefy viscera and muscles. The juices can be withdrawn and then the body juices of the prey sucked off by conversion of [6] the pharynx to a reciprocating pump. The larva's sensory equipment includes [7] numerous organs capable of recording the tiniest mechanical vibration of the support. Let but a grain of sand trickle down the walls of its tunnel, and the larva, instantly alerted, gets ready to leap on the possible prey with its mandibles gaping wide. To struggle with the prey, the hunter needs to get a firm grip on the substratum. It is able to do so because [8] the rear end of its abdomen bears chitinous hooks that bite like teeth into the substratum and prevent slipping. The ant lion's habitat does not support a plentiful fauna, and starvation often occurs. For days on end the sedentary larvae lie hidden in the sand at the bottom of their funnel-shaped trap, on the lookout for possible prey, ant or other insect. But their physiology enables them to fast for long periods without dying. Since the larva lives in very dry sand, often sheltered from the rain, it can only survive by avoiding all losses of moisture. Its excretory function operates economically and [9] resorbs the water containing its urine and other waste. What is more, [10] the digestive tract ends at the junction of intermediate and lower intestines so that all defecation becomes impossible and the water absorbed with the food is totally conserved. In addition, the ant lion larva is protected against evaporation by [11] exceedingly impermeable integuments. Obliteration of the rectum from the digestive system enables it to be transformed into [12] an organ having a new functions that of silk tank and spinner. It dilates into a blister whose tip forms a fold into which the free extremities of the excretory organs or Malpighian tubes (cryptonephridism) penetrate, an arrangement facilitating resorption of the water in the urine. The segments of the Malpighian tubes nearest to their insertion into the intestine [13] alter in function, no longer excreting waste but secreting silk made of proteins and accumulated in the reservoir of if the ex-rectum. Through [14] the very narrow anus, which serves as a spinneret, the fully grown larva ejects the silk and, like a caterpillar, spins a cocoon in which, a few weeks later, it undergoes metamorphosis into a perfect imago." (Grasse P.-P., "Evolution of Living Organisms: Evidence for a New Theory of Transformation," Academic Press: New York NY, 1977, pp.161-163. Emphasis in original)

Grasse continues with a question for the Darwinists: "How many chance occurrences would it have taken to build this extraordinary creature ... It is not enough for a property to appear, it has to come at the right time ... [and] in a certain order" (my emphasis):

"So we now have to turn to the Darwinians and ask: `Have you ever seen a mutation simultaneously affecting two separate components of the body and producing structures that fit one another precisely? Tell us, have you ever beheld three, four, or five simultaneous mutations with matching structures producing coordinated effects? And yet you have observed and described thousands upon thousands of mutations. The huge populations of animals and humans bear witness to their frequency. In any man the number of mutated genes is extremely high. The mutations are nondescript, monstrous, or pathological, and are invariably, repeat, invariably incoherent. And yet it is by that that you claim to explain the biological order, and make evolution intelligible?' These are vital questions that demand an answer. There is no way of getting around them, or evading the issue. Every biologist who wants to know the truth must answer them, or be considered a sectarian and not a scientist. In science there is no `cause' to be defended, only truth to be discovered. How many chance occurrences would it have taken to build this extraordinary creature that braves the burning sands of the Sahara, endures prolonged fasting, economizes water, detects the slightest vibration in the ground, lies in wait for days on end at the bottom of a funnel, or goes forth, freely, to hunt down its prey? It is not enough for a property to appear, it has to come at the right time. These accidents, always fortunate of course, produced their effects by occurring in a certain order, for, out of order and untimely, they would have remained imperative [inoperative?]. What scientist would venture to estimate the chances of such a cascade, such an avalanche, of coordinated and mutually adjusted chance occurrences? The odds are infinitesimal." (Grasse P.-P., "Evolution of Living Organisms: Evidence for a New Theory of Transformation," Academic Press: New York NY, 1977, p.163. My emphasis)

Interestingly Darwin, while in Australia on his journey around the world in HMS Beagle, observed an ant-lion catching a fly, and he wrote in his diary at the time that "so beautiful, so simple & yet so artificial a contrivance" (the latter being Paley's favorite term for evidence of design!) occurring in different species of what must be then same genus in both Europe and Australia, was evidence that "The one hand [i.e. "the Creator"] has surely worked throughout the universe":

"January 18, 1836, New South Wales: `A little time before this I had been lying on a sunny bank & was reflecting on the strange character of the animals of this country as compared to the rest of the World. An unbeliever in everything beyond his own reason might exclaim, 'Surely two distinct Creators must have been at work; their object, however, has been the same & certainly the end in each case is complete.' Whilst thus thinking, I observed the conical pitfall of a Lion-Ant: a fly fell in & immediately disappeared; then came a large but unwary Ant. His struggles to escape being very violent, the little jets of sand described by Kirby (Vol. 1. p. 425) were promptly directed against him. His fate, however, was better than that of the fly's. With out doubt the predaecious Larva belongs to the same genus but to a different species from the European kind-Now what would the Disbeliever say to this? Would any two workmen ever hit on so beautiful, so simple & yet so artificial a contrivance?. It cannot be thought so. The one hand has surely worked throughout the universe. A Geologist perhaps would suggest that the periods of Creation have been distinct & remote the one from the other; that the Creator rested in his labor.'" (Darwin C.R., in Gruber H.E., "Darwin on Man: A Psychological Study of Scientific Creativity," together with Gruber H.E. & Barrett P.H., "Darwin's Early and Unpublished Notebooks," Wildwood House: London, 1974, p.438. My emphasis)

PS. The above was what Darwin wrote in his diary on board HMS Beagle. But after he had returned to England and started work on his theory of evolution in 1837, Darwin published his Journal of Researches (later renamed "The Voyage of the 'Beagle'") in 1839, and relegated the diary entry to a footnote as well as editing out his references to the ant-lion's "beautiful, so simple & yet so artificial a contrivance" and "the Creator":

"* I was interested by finding here the hollow conical pitfall of the lion-ant, or some other insect: first a fly fell down the treacherous slope and immediately disappeared; then came a large but unwary ant; its struggles to escape being very violent, those curious little jets of sand, described by Kirby and Spence (Entomol., vol. i., p. 425) as being flirted by the insect's tail, were promptly directed against the expected victim. But the ant enjoyed a better fate than the fly, and escaped the fatal jaws which lay concealed at the base of the conical hollow. This Australian pit-fall was only about half the size of that made by the European lion-ant." (Darwin C.R., "The Voyage of the 'Beagle'" [1845], Edito-Service: Geneva, n.d., reprint, p.442)

It now sounds like Darwin's first thought was the right one!

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"

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