v1.2.2 / chapter 16 of 28 / 01 aug 08 / greg goebel / public domain
* Much of the evidence for Darwinian evolution was outlined by Darwin himself, and remains just as valid now as it was in 1859. This chapter recapitulates and updates some of his core arguments.
* The discussion of the evolution of the eye demonstrated a basic principle of Darwinian evolution: the spectrum of forms of a particular structure, illustrating how the structure could have emerged in a Darwinian fashion. Darwinism insists that species emerge by slow microevolutionary changes, one step at a time -- "natura non facit saltum". Furthermore, as implied in the discussion of the evolution of the eye, each one of these changes must provide a selective advantage over the status quo, or it won't be perpetuated: more formally, there are no "non-functional intermediates".
The notion of non-functional intermediates seems to raise a challenge to Darwinism. It's like the story about Alice trying to get across a canyon to visit Bob, rearranged to have Alice get across a river by walking on sets of stepping stones that were luckily arranged to allow her to make the crossing one sure, solid step at a time. What are the odds? They don't sound good, and they sound like they should get worse for greater evolutionary changes -- that would mean more lucky stones. As one critic put it: "The more intermediate evolutionary steps that must be climbed to achieve some biological goal without reaping a net benefit, the more unlikely a Darwinian explanation." This criteria that every step in a long chain of steps provide a "net benefit" makes Darwinian evolution sound absolutely impossible.
This is another line of reasoning that seems plausible on the surface but, once again, is muddled in its comprehension of how Darwinism works, envisioning it as a greased pole instead of a staircase. Consider a scenario for the evolution of a particular organism from an earlier species, visualized again as a video with one frame per generation to show the morphing of one species into another. The video seems to show the organism changing smoothly and progressively in a magically directed fashion from beginning to end. It only looks like that because the video was constructed with a particular endpoint as an anchor: it is viewed in the forward direction but it was assembled by retracing the steps from the endpoint back to its origin. The organism is actually evolving along several different lines per generation. Several videos could be made to show the same organism evolve into distinctively different species -- think of Darwin's finches -- though most of the branches are dead ends, often dying out quickly because the modification didn't provide any selective advantage, or immediately because it was downright disastrous.
The story also assumes that Alice is trying to find her way to Bob. Once again, the Darwinbot -- Darwinian evolution -- isn't going anyplace in particular at all, it's just wandering over the fitness landscape, the only guide for the wanderings being that it move uphill toward fitness peaks. Even this requirement isn't entirely strict. Due to genetic drift, it is also possible for the Darwinbot to negotiate "downgrades", at least to a small extent -- this extent becoming greater if the species isn't under strong selection pressure.
In addition, in any generation of an organism, there's likely to be tiny changes among some of the members of the population that provide a slight selective advantage -- any changes, any selective advantage. Again, the fitness landscape, while it is visualized in terms of hills and valleys, is a sheer abstraction of a "surface" with many dimensions, with every applicable measure of "fitness" adding its own dimension. That by implication means that there's a lot of possible "uphill" paths -- if the organism reaches a peak by one measure of fitness, it can still be moving uphill by some other measure.
In summary, the Darwinbot is simply roaming over the fitness landscape, driven one advantageous step at a time by mutation and selection, without considering anything but the next step. The likelihood of having some advantageous next step available is good. One species emerges from another through a long sequence of such steps, with the particular end result merely being where the evolutionary process ended up. It only looks specified in hindsight; the Darwinbot could have gone in any number of directions, obtaining different results. There is nothing surprising about the fact that the steps were all functional, since any branch that took an unworkable step died out and disappeared. We only see the results of the ones that didn't.
The question of non-functional intermediates seems valid at first, but it ends up being a red herring, another attempt to declare a "magic barrier". Once again, the language analogy holds. One language will morph into another over time through slow, small, unplanned changes. None of the changes are going to take hold unless the speakers of the language find them useful, advantageous. At all steps the language remains fully functional -- there's never any unworkable "intermediate language". The process could proceed until there is no recognizable resemblance between the two languages and never run into any "magic barrier", and there is no "blueprint" to show where it will end up: languages are not as a rule the product of a predetermined overall design.
Nobody sees this scenario as unreasonable or even troublesome. How else would it work? The critics are in effect saying that the notion that Alice could actually take a long series of individual steps, all of which had to be effective steps, to walk to Bob's house is hard to swallow, and the more steps she had to take, the more impossible it is to believe. To be sure, it might be difficult to figure out the precise steps she actually took, but belaboring this issue ends up being another ploy, proclaiming in effect that if we can't prove the exact steps Alice took to get to Bob -- then she must have teleported.
* It is true that this stepwise progression demonstrates evolution, but not necessarily Darwinian evolution by natural selection. However, it certainly does not suggest Design. The progression of forms would seem hard to explain in terms of Design -- why bother with all the rigmarole? Why not do the entire job at once and be done with it? Why would the Designer have to fiddle with a series of prototypes instead of just coming up with the final "production" Design right away? "Just because"?
One reply to this objection is to acknowledge that evolution takes place, but claim it is guided by Design interventions. However, that still doesn't explain the need for the rigmarole, and all this ploy amounts to is admitting that the evidence points to Darwinism but then tapdancing Design around evasively to dodge the bullet. As the tapdancing converges to its ultimate extreme of detail -- for example claiming that every lucky mutation in an evolutionary process is actually a Design event, caused by some tiny zap from the Designer, with the more common unlucky mutations apparently being bad shots -- it keeps backing itself into a corner, becoming ever more difficult to distinguish from Darwinism. Ultimately, it ends up declaring Darwinism to be Design in disguise, and at this point the "copycat Designer" begins to seem more than just slightly devious.
* Anyway, back to the example of the eye. It can be shown to have evolved by tiny steps, each of which gave a selective advantage. What good is 5% of an eye? A primitive eyespot isn't even that much of an eye, but it's still useful. By the same reasoning, critics look at the "sea dragon", a species of seahorse that looks exactly like a clump of seaweed, and assert that natural selection could never produce such an elegant adaptation. They claim it would do no good to look only 5% like a clump of seaweed.
On the contrary: wouldn't a fish that looked 5% like seaweed have a marginal advantage? Wouldn't a predator have more trouble spotting it from a distance or under poor viewing conditions? Natural selection is based on such incremental advantages.
It should be emphasized again that natural selection works on populations; "a fish" doesn't mean a single fish, it means a population of interbreeding fish. That population will have a variation in characteristics around a mean value, with the distribution of those variations making up what could be loosely visualized as a bell-shaped curve, just as there's a bell-shaped curve of the distribution of heights of adult human males. It's not really a simple question of two fishes, one which has achieved a jump in its resemblance to seaweed relative to the other, but of an entire population in which there is a continuous range of appearances, with one end of the range clearly looking less like seaweed and the other end of the range more like seaweed.
The fish on the outlier of that curve that looked less like seaweed would be slightly more vulnerable to predation to those on the other outlier of the curve that looked more like seaweed, causing the mean of the curve to very gradually shift towards the component of the population that looked more like seaweed. This cycle of ever improving seaweed impersonations started by accident: due to its ancestral history and other adaptations, the fish already looked slightly like seaweed by accident, and random changes then enhanced the effect, with natural selection ramping up the evolutionary treadmill through its "differential screening".
Eventually the fish obtains a highly optimum resemblance to seaweed, and the probability of obtaining a mutation that improves the resemblance starts falling off, while the probability increases of mutations that will degrade it. The fish has effectively reached the peak of that hill on the fitness landscape, and then the differential screening will trim away at both ends of the distribution, squeezing it in towards the center and resulting in a highly uniform, well-tuned population of fish that look surprisingly like seaweed. Incidentally, it should be noted that the fish is certainly going to be under other selection pressures that may move it off in other evolutionary directions, and possibly compromise its neat resemblance to seaweed.
For another example, consider aquatic adaptations. Stephen Jay Gould once famously quoted a critic who suggested that adaptation of mammals to a marine environment posed a major problem for Darwinism:
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Darwinists rarely mention the whale because it presents them with one of their most insoluble problems. They believe that somehow a whale must have evolved from an ordinary land-dwelling animal, which took to the sea and lost its legs ... A land mammal that was in the process of becoming a whale would fall between two stools -- it would not be fitted for life on land or at sea, and would have no hope for survival.
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It has to be conceded that a smarter critic would have known this argument could be easily demolished with a moment's thought. Polar bears spend a good amount of time in the water but don't seem at least superficially to be particularly optimized as water creatures. River otters are better off in this regard, and sea otters better still; sea lions take the level of adaptation to the water one step further, while true seals are so adapted to life in the sea that they find it difficult to get around on land. The whale is the endpoint of this spectrum, totally optimized for life in the sea, so much so that it will die if it goes onto land.
Of course, the variation from otter to seal to whale does not imply that otters and seals are ancestors of whales and dolphins -- nobody believes that -- but it takes little imagination to think that whales are descendants of partially-aquatic creatures along such broad lines. The fossil evidence for transitory forms leading to modern whales and dolphins was thin on the ground for a long time, but from the 1980s paleontologists found a series of fossils that bridged the gaps -- not merely finding the skeletons of whales with fully functional rear fins, but even finding the fossil of a whale-like amphibious creature, Ambulocetus natans, with four oversized feet that were clearly capable of carrying the beast around on land. The animal's rear spine suggested musculature that helped it swim by arching its spine up and down, in much the same way as an otter.
Birds such as penguins have also returned to the sea. One of the fascinating observations of penguins swimming in a tank in a zoo is that they swim using their forelimbs, their wings, with their tail and feet playing a strictly supporting role. It takes little imagination to see the Darwinian principle of "leveraging off what's already available" in action: the penguin "flies" underwater in a fashion not broadly all that different from the way its ancestors flew through the air. Interestingly, although sea lions and true seals are closely related, they swim in different fashions, with sea lions (and walruses) obtaining propulsion from their front fins like the penguins, while seals use twisting motions of the body ending in the tailfins -- a neat example of the branching nature of Darwinian evolution in action. Whatever works.
Similar thinking applies to the adaptation of animals to land. Critics of Darwinism deride the idea of the first fish that somehow "decided" to crawl out of water, but in fact there are a number of different species of fish that can flop around on land and go cross-country, most notably the "walking catfish" of Southeast Asia that has been making a nuisance of itself in the American South since it was carelessly introduced there some years back.
The walking catfish doesn't do a particularly impressive job of getting around out of water. The froglike mudskipper, another Southeast Asian fish, is better adapted to land locomotion -- while amphibians like frogs are still better adapted to life on land, though as a rule they still must lay eggs in water.
There are cases where it actually is hard to see how there could have been a gradual progression of forms. Birds, bats, and the extinct pterosaurs have wings that are obviously modified legs, with the wings all derived from a pre-existing structure, as Darwinism says they should be -- it might have been literally "handy" for bats to have retained their front legs and grown wings on their back to look like tiny devils out of Dante, but Darwinian evolution doesn't work that way. However, insects have wings that are clearly unrelated to legs. The general belief is that insect wings began life as a structure for another purpose, possibly a panel to absorb sunlight or radiate heat, with the structure proving useful for gliding purposes. Models have been constructed to show how it could happen, but they remain argued.
Such "indirect pathways" are called "preadaptations", though since this term tends to falsely imply that some biostructure was deliberately obtained just because it might come in handy later, some prefer to use the more obscure but less loaded term "exaptations" instead. Critics often call such exaptations contrived, but there are plenty of examples that are hard to refute. One of the famous examples, promoted by Gould, is the "panda's thumb". A panda is a bear adapted to eating bamboo shoots -- an unusual practice for a bear, though given the prevalence of bamboo in Asia a practical habit -- and unlike other bears it has a "thumb" on its forepaws to help strip down the shoots for consumption. The "thumb" turns out to be nothing more than an extension of a normal bone in a bear's paw, the "radial sesamoid", that proved useful. The panda's thumb isn't much of a thumb, but it works.
Bears tend to be "handy" creatures, sitting or standing and using their forepaws as manipulators, and the panda has simply taken this process to a specialized extreme. In fact, in a sense the panda itself is something of an example of indirect pathways: who would have imagined a bear, a member of a family of carnivores, that eats grass for a living?
* Darwin's theory was partially based on consideration of the taxonomic tree of species originally laid out by Linnaeus, and the tree of life is still regarded as a cornerstone of the concept. The reasoning starts out as a bit subtle and arguable, but builds up credibility as it is developed.
The tree of life clearly shows the existence of families of organisms. Among the mammalian carnivores there is a family of cats, such as lions, tigers, cheetahs, and wildcats; a family of dogs, such as wolves, jackals, foxes, and domestic dogs; a family of bears, including grizzly bears, sun bears, and panda bears; and so on. The reality of this familial tree was well established, on the basis of physical details, even as far back as Darwin's time, though there was considerable dispute over special cases and the details. As discussed later, modern genetic evidence has confirmed that the taxonomists of the past were generally on the right track, though many tweaky corrections and elaborations have been introduced.
The idea that there is a range of species collected in different families is not on the face of it incompatible with Design, since it can be argued that different creatures were Designed for different roles and that a set of familial templates or a set of "common Design" principles were involved in the Design process. As mentioned, Richard Owen presented this argument in response to Darwin early on, and it is still floating around today. However, this sounds hard to tell from a "just because" story -- "they seem to be related because they were made that way", the copycat Designer at work.
The entire concept of "biological relationships" strongly implies a "familial relationship", and the notion of a family equates to common descent. If there was some isolated human community where the population could be roughly arranged in three groups with common names and distinct physical similarities within each group, it wouldn't be a shock to think that the entire population of the community descended from three distinctively different founder families. It is just as natural to think that all the different species of cats had a common ancestor.
The tree of life makes very little sense without assuming common descent; up to the era of Linnaeus and Darwin there were a large number of theories put forth to explain the taxonomic organization of species, but in hindsight they sound like little more than arbitrary schemes for categorizing the books a library. Much the same could be said for a modern taxonomic scheme proposed by Design advocates known as "baraminology", in which organisms are divided into groups of "created kinds" -- that is, a handful of basic "kinds" were Designed, with microevolution then leading to variations within (but not outside of) each "kind".
The fact that the boundaries between members of a species are often indistinct enhances the credibility of common descent. Wolves can interbreed with dogs -- in practice usually the larger ones because wolves tend to regard smaller dogs as prey -- and produce fully functional offspring. Lions and tigers can produce offspring, but they are generally sterile. More widely differing species cannot interbreed at all. From the point of view of Design, this gradual separation of species is "just because", but from the point of view of common descent, it's perfectly sensible, analogous to the way a language taken up in two different locations gradually drifts apart into two dialects, and then finally distinct languages.
Wolves and dogs are still close together on the taxonomic tree, implying they only split apart recently. Lions and tigers are farther apart, which suggests they split apart some longer time ago. Interestingly, about ten percent of human couples can't conceive, and of these couples roughly tenth are perfectly fit as far as their reproductive facilities go; the only explanation anyone has come up with is that they are suffering from a genetic incompatibility. To be sure, nobody disputes that all humans are the same species, but the couple may well have specific features in their genomes that make it difficult for them to pair up. The couple in effect came from the extreme ends of a "genetic compatibility" distribution; had the husband and wife chosen different mates closer to the center of the distribution, they wouldn't have had any problems.
If this is so, it would be strong evidence for the way that gradual genetic drift can set up reproductive barriers. There are clearer examples of the emergence of such reproductive barriers in nature, for instance with pink salmon. Since salmon have a life-cycle that takes them up rivers and streams to spawn every two years, that means there are two groups of salmon, "even-year" salmon and "odd-year" salmon, that do not normally breed with each other. As it turns out, it is difficult to cross-breed even-year and odd-year salmon despite the fact that they are difficult to tell apart.
* Now consider the way species vary with location. All species are subject to a greater or lesser degree of genetic drift all the time, obtaining genetic changes that either have no visible effect or result in traits even fairly significant ones, that neither impair or enhance survivability. Under Darwinism, separated members of the same species inevitably become increasingly dissimilar. There are distinctive families of primates in the Old World and New World, with easily identified distinctions. There are no baboons in the New World; there are no marmosets in the Old World. Under Design, the two families of primates are arbitrary; why not just have one? Under common descent, they are two branches of a common ancestral family that split apart a long time ago.
This sort of geographical distribution of families of organisms fascinated Darwin, with the distribution of finches among the separate islands of the Galapagos ending up being a particularly interesting example. The pattern of the species of Darwin's finches suggested that ancestral finches arrived from South America and became established, radiating out into species differing in appearance and habit. The alternative is to say that Design set up a group of finch species that all just happened to look like a South American finch, with the different island finch species being tweaked to play out ecological roles occupied by completely different bird species on the mainland.
Sometimes apparent anomalies in geographic distribution end up confirming the rule instead of breaking it. Camels are found in the Old World, while their close relative the llama and its kin are found in South America. This was puzzling to evolutionists at first, leading to the conjecture that camels were once common in North America but died out. Fossils of extinct camels were eventually discovered in North America, including those of the giraffe-like Aepycamelus AKA Alticamelus. In fact, it seems that camels originally came from North America.
One particularly interesting example of biogeographical variation of organisms is the tendency of isolated islands to acquire unique sets of species, as Darwin noticed in the Galapagos. The large island of Madagascar is noted for its unusual species. Madagascar has been geologically isolated for 90 million years; although it is not all that far from Africa in the current era, its wildlife is almost entirely different from that of Africa, in particular lacking any large native species of ungulates. It includes a fascinating set of species of lemurs, which are only represented in Africa by the bush babies and pottos, while there are no monkeys or apes in Madagascar.
It appears that the ancestors of Madagascar's lemurs arrived tens of millions of years ago by a "rafting" event, in which they floated over the sea on uprooted trees or the like. This sounds like an implausible notion, but it has been observed in modern times, and in fact hurricanes can tear up so much vegetation that the rafts look like small islands, swarming with various animals. It is admittedly rare, but over millions of years events of low probability become a near certainty.
In any case, since that time, their lineage has been pushed to one side in Africa by the monkeys and apes, while they thrived in Madagascar. There was once a huge ground-living lemur there, the size of a bear, and in the current day the family includes, in sadly small and shrinking numbers, the notoriously bizarre nocturnal "aye-aye", named for its cry. It is the ecological equivalent of a woodpecker, with forepaws featuring a long and thin middle finger, which it uses to search for and dig out insects burrowed into trees.
One of the more spectacular stories concerning the adaptive radiation of species in isolated environments concerns the "cichlid" (pronounced "sick-lid") fish of Lake Victoria in Africa. Cichlids are bony fish with an unusual adaptation: they have a second set of jaws set back in the throat. That would be intriguing in itself, but what makes the cichlids of Lake Victoria more fascinating is that there are hundreds of species of them, all closely related to each other, and relatively distantly related to other cichlids. There are also cichlids in Lake Tangyanika and Lake Malawi, but the species are different in each of the three lakes.
Lake Victoria was formed about 100,000 years ago, setting a time bound on how long it took to produce the hundreds of species of cichlids in the lake. In addition, borings from the bottom of Lake Victoria show that is carpeted with a layer of dead grass, dated from 14,500 years ago. At that time it largely dried up, being reduced to a set of separate small lakes and ponds. Each pond became a separate ecosystem, an "island" of water surrounded by land, in which the cichlids underwent rapid diversification. Once the lake filled back in again, the expanded numbers of species became parts of an expanded ecosystem. It appears that this cycle occurred several times over the last 100,000 years, driving the wild speciation of the cichlids.
* It again could be argued that familial descent and its linkage with geographic distribution are evidence for evolution but not Darwinian evolution. However, once again the evidence clearly doesn't suggest Design. Why fill up Lake Victoria with dozens of species not found elsewhere, and in particular why would they be closely related? It makes sense under Darwinism; for Design it's "just because".
* Going back again to the example of the eye, it is often presented as a disproof of Darwinism because it seems so perfect. The same can be done with other awesome adaptations, such as the species of praying mantis that looks like an orchid and sea dragons that look exactly like clumps of seaweed. As discussed above, they don't really amount to a disproof, but for a persuasive argument, we need to look elsewhere. As Stephen Jay Gould put it:
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... ideal design is a lousy argument for [Darwinian] evolution, for it mimics the postulated action of an omnipotent creator. Odd arrangements and funny solutions are the proof of evolution -- paths that a sensible [Designer] would never tread but that a natural process, constrained by history, follows perforce. No one understood this better than Darwin.
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Gould was specifically referring to Darwin's 1862 paper on the elaborations of orchids, which have a fascinating set of mechanisms to make sure that pollinators like bees were thoroughly dusted with pollen. Darwin's insight was to point out that, although these mechanisms were sometimes spectacularly elegant, they were variations on existing flower structures -- they had not been "invented" from scratch for the task. As Darwin put it in his paper:
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Although an organ may not have been originally formed for some special purpose, if it now serves for this end we are justified in saying that it is specially contrived for it. On the same principle, if a man were to make a machine for some special purpose, but were to use old wheels, springs, and pulleys, only slightly altered, the whole machine, with all its parts, might be said to be specially contrived for that purpose. Thus throughout nature almost every part of each living being has probably served, in a slightly modified condition, for diverse purposes, and has acted in the living machinery of many ancient and distinct specific forms.
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Darwin's language about a machine assembled of existing parts being "specially contrived" is a bit hard to interpret, due to his Victorian writing style and patterns of reasoning -- but in the light of Darwin's basic principles, it seems he was observing that even if a machine were improvised out of existing parts, there's no reason that it couldn't end up being so effective that it would seem perfectly Designed for its purpose.
There is a saying that nature, in the Darwinian vision, is an excellent tinkerer. It is in evidence of such tinkerings and improvisations -- the use of "old wheels, springs, and pulleys" -- that the work of Darwinian evolution can be perceived. This notion was implicitly introduced above in the examples of bat or bird wings being derived from forelegs and the panda's thumb. Consider the eukaryotic cell. What sense would it have made to specifically Design the cell with organelles -- the mitochondria and chloroplasts -- with their own degenerate genomes? This "thrown together" construction is clear evidence of the evolutionary origin of the eukaryotic cell as a symbiotic arrangement of prokaryotes. Under Design, it's "just because".
For a particularly vivid example, there are two broad classes of bottom fish: skates and rays versus halibut and other flatfish. They are only similar in a general fashion; they couldn't otherwise be much more different, and the way in which they differ points straight to Darwinism.
Skates and rays are cartilaginous fishes, lacking real bone, making them part of the same family as sharks. Sharks tend to be relatively flattened fishes, and so once they took up bottom-feeding habits there was an evolutionary tendency to become flattened further to allow them to hug the bottom for concealment and defense. Some species of dogfish -- bottom sharks -- show this tendency somewhat, but it becomes much more pronounced in the skates and the rays.
The rays seem to be an elegant Design for a bottom-feeder. Now consider the halibut and its kin. The halibut is a bony fish, like trout or herring, and the mark of such fish is that they are flattened vertically, with a cross section that is narrow and tall. The simplest way for such a sort of fish to become an efficient bottom-feeder was to turn on its side, and that's exactly what the halibut did. A halibut actually starts life as a more or less ordinary bony-fish fingerling, but as it matures it turns sideways and one eye migrates to the other side of its head.
* This is a totally inelegant approach to becoming a bottom-feeder, what an engineer would call a "kluge" and an ugly one at that, but it works and works well enough. Natural selection can achieve elegance but cares nothing about it, "works well enough" does the job. There is a misperception that evolution by natural selection can be expected, given enough time, to produce perfect solutions, but in reality it merely provides "cost effective" solutions. It's not so much "survival of the fittest" but "survival of the fit enough".
In this context, evolutionary scientists like to point out that the human eye, the classic example of the Reverend Paley, has an interesting feature: the retinal nerve connections that link the eye's photoreceptors to the optic nerve are actually on a layer that covers the photoreceptors -- light has to pass through the layer of neural connections to reach the photoreceptors buried under it, and one of the consequences of this organization is that there's a small "blind spot" in the center of our field of view. Our eye actually works fine, but engineers wouldn't call this a kluge -- they'd call it inept. The eye of the octopus and squid gets it right, with the photoreceptors on top and no blind spot. In addition, in the mammalian eye the retinal layer is weakly attached to the back of the eyeball and can be knocked loose relatively easily by a blow, resulting in the "detached retina" that often afflicts boxers.
It is also noteworthy that the compound eyes of insects are inherently low resolution. To match the resolution of the human eye, they'd have to be a meter in diameter. If they had been Designed, a camera-type eye system would have more room for growth. As mentioned, spiders have camera-type eyes and some species of jumping spiders have very good vision -- they get around the limitation of a small and inherently low-resolution retina by mounting the retina on an "arm" and scanning it around to build up a detailed image. Once again, the compound eye "works well enough", but it's hard not to think that insects got the second prize in the Darwinian lottery.
There are plenty of other examples where the improvisation of nature is obvious:
Even entire organisms can end up being poorly "Designed", the best example being the flightless birds on isolated islands, most particularly the dodo bird -- the fat, flightless pigeon of the island of Mauritius. Evolving in an environment where a fair-sized bird wasn't confronted with predators, the dodo lost the ability to fly and protect itself. When humans showed up, bringing along rats and pigs, the dodo was defenseless and died out quickly. Darwinian evolution, in its blind and stupid way, set it up the dodo for a fall, leading it down a dead-end path. In fact, flightless birds are fairly common on remote islands -- or at least they were until humans and their camp followers showed up and demonstrated a tendency to wipe them out.
Indeed, species obviously often go extinct, their "Designs" being no longer adequate to the challenges they faced. Why would a Designer keep wanting to build new organisms and then throw them away? "Just because"? Under Design, extinction is arbitrary; under Darwinism it's almost inevitable. If one species is displaced and driven to extinction by another, better-adapted species, is this because the Designer, after scratching His head, got around to figuring out how to build the "new improved model" -- or is it evidence of Darwinian competition in action?
* There is also the evidence provided by vestigial organs -- the most famous being the wings of flightless beetles, sealed away forever under a hard carapace. Other well-known examples are the broken eyes of cave fish, wings of the flightless ostrich, the degenerate rear wings of damselflies -- and impacted wisdom teeth, the elegant Design in which we try to grow more teeth than our jaw will accommodate. One particularly interesting vestigial structure is the "fibula", which is the "toothpick" of bone found when eating a chicken or turkey drumstick; it is clearly of no real structural importance, being nothing more than a remnant of the two-boned structure of the leg of a carnosaur.
Critics will point out that such vestigial structures are not necessarily useless, for example that the vestigial wings of a flightless beetle provide additional armor for the beetle's back. However, under Design it would seem to have been much more sensible to provide thicker back armor than go through the trouble of burying useless wings in the beetle's back for this purpose. Similarly, the ostrich's wings are used for balance and courtship display, while the degenerate rear wings of damselflies vibrate to provide flight stabilization -- but in both cases these are clear adaptations of what obviously used to be wings for flying, a notion which also doesn't make much sense under Design.
* It should be noted that the improvisations and occasional dead-end stupidities in biosystems are not absolute disproofs of Design. They may just demonstrate that the Designer is an incompetent, as dumb as the dodo bird, making the fact that the results seem to more strongly imply natural selection strictly a coincidence. In other words, Design is a copycat right down to being every bit as blind and short-sighted as Darwinian evolution. Few advocates of Design find the "dimwit Designer theory" particularly attractive, and those that do, don't find it a sales pitch that impresses anyone with the slightest amount of skepticism.
It is also occasionally suggested that biosystems that appear to be poorly Designed actually are well Designed -- we just don't understand them well enough to appreciate it. The immediate response is that biosystems that seem well Designed are actually poorly Designed -- we just don't understand them well enough to appreciate it. Obviously, if we're not competent to pass any judgement on whether some biostructure is well-Designed or not, then nobody can hold up the eye as evidence of Design any longer. In fact, absolutely nothing could be held up as evidence for Design, and the entire "argument for Design" would effectively fall over and die. All this amounts to is playing the game of "heads I win tails you lose" and, once again, nobody with any skepticism is impressed.
* The evidence of such opportunism supports evolution by natural selection, suggesting emergence of "whatever solution works" by "trial & error" processes, instead of consistent Designs according to some formal plan.
So does the fact of "convergent evolution", Sometimes selection pressures produce organisms that look very similar, or have similar features, but have widely different evolutionary roots and differ greatly in their details. The eyes of humans and squids are functionally similar but completely different in basic small details. Bats use sonar; so do whales and porpoises, though they aren't any closer relations to bats than we are.
Porpoises look much like sharks, but it's obvious that air-breathing porpoises used to be land animals. One big giveaway is that most whales and porpoises still have a set of vestigial, completely useless rear leg bones in their tails. In fact, if they had been built according to a specific blueprint to be sea creatures, they'd have gills and wouldn't need to come to the surface to breathe on a regular basis -- though admittedly, given their adaptations for "holding their breath", this isn't much more of an inconvenience than having to urinate every now and then. The extinct reptilian icthyosaurs provide another example along the same lines, once again being obviously the descendants of ground-living organisms that were shaped by selection into the shark-dolphin mold.
Australia, geographically isolated for at least 55 million years and possibly longer, is a Madagascar-like zoological wonderland made large. The continent produced marsupial anteaters, marsupial flying squirrels (gliders), and a marsupial equivalent to a wolf, recently extinct, called a "thylacine". Australia also produced a marsupial mole that is hard to tell from the moles recognized in Europe and America.
To add another piece of convergence to the evolutionary puzzle, the golden moles of southern Africa, which look like perfectly ordinary moles, are more closely related to elephants than they are to ordinary moles. It is a bit puzzling that reptiles don't appear to have ever produced a mole form -- insects have, in the form of burrowing "mole crickets" -- and it might be gratifying if paleontologists actually find a fossil of a reptilian mole one of these days. Its adaptations would certainly make its lifestyle immediately obvious.
Not too long ago, at least by geological standards, the Australian thylacine had a South American cousin that looked like a sabre-tooth tiger -- though it "improved" on the feline sabre-tooths by featuring bony sheaths in the front of the jaw to protect the relatively brittle, fragile sabre teeth. In fact, even ignoring the marsupial sabre-tooths, there were actually two independent groups of sabre-tooths, including a group among the "true felines" and a separate group of "false cats", each being "reinventions" of the same concept within related groups, and it appears that they repeatedly evolved within the groups. Sabre-tooths were adapted to hunt large prey, able to perform a quick kill on a strong and dangerous victim by plunging the sabreteeth deep into the victim's throat. Saber-tooths tend to go extinct when conditions change and large prey is hard to find, becoming a victim of their own short-sighted specialization; then the cycle begins all over again, to eventually result in another variation of sabre-tooth.
There are porcupines in both the Americas and in Africa, but aside from both being rodents, they are not closely related, and in fact their resemblance is superficial. Although the quills of both are obviously modified hairs, American porcupines have short quills that come out easily and have a nasty spiral grain that makes them hard and painful to remove, while African porcupines have long spines that don't come out. (By the way, one African porcupine species actually has rattles on its back among its spines to give troublemakers a hint to leave it alone -- a touch of convergent evolution with rattlesnakes.) Ants and termites appear very similar, but other than being insects they are entirely different creatures -- termites are very closely related to, and more or less a colonial form of, cockroaches.
Incidentally, one interesting "exception that demonstrates the rule" to the wide-ranging parallels among marsupials and placental mammals is that no marsupials ever obtained flapping-wing flight. The reason is obvious: the placentals lucked out in Darwinian lottery first, resulting in the bats, and since bats could fly, they were able move into the lands of the marsupials. The marsupials couldn't move into that niche, since it was occupied already.
* On the other hand, the "trial & error" nature of Darwinism can lead to entirely different implementations of organisms or their features that perform the same functions. Spider versus insect eyes are a classic example. Ducks and grebes are similar water birds, but a duck has webbed feet, while a grebe has large flaps on the sides of its toes.
Imagine a large herbivore of the grasslands whose defense is speed, escaping a predator by running away as fast as possible. One approach is the antelope or the horse, with four hoofed, long legs. Australia came up with a different approach, the kangaroo, with twin strong rear legs for bounding plus a heavy tail for balance and additional boost. To close the circle, however, convergent evolution has recreated this same configuration in other animals, specifically among rodents -- such as the kangaroo rat of American deserts and the wallaby-sized springhare of Africa.
Darwinism is also reinforced by the fact that there is a good degree of diversity among kangaroo species. I recall the absolute unbelieving look I got from an acquaintance one time long ago when I told him about tree kangaroos. There really are kangaroos that live in trees -- though not surprisingly they really only share a broad familial resemblance with their larger ground-living cousins.
* The essential message of the notions of convergent and divergent evolution in the context of Darwinian evolution is that they demonstrate the principle of opportunistic adaptation -- whatever works. Consider flight: we have flapping-wing insects, birds, reptiles, and mammals; flying squirrels and marsupial gliders; flying fish; snakes that can flatten their bodies for aerial leaps, as well as lizards with expanded rib cages to perform the same trick; and even frogs, the Wallace tree frog discovered by Alfred Russel Wallace, that use expanded webbed feet to help them sail through the air.
Critics ask: "What good is half a wing?" -- oblivious to the fact that there all kinds of intermediate wings in nature: "It's 1% better than 49% of a wing." There is a range of "solutions", some very similar, some completely different, which is just what would be expected.
The notions of convergent evolution, the same forms arising repeatedly, and of divergent evolution, different forms arising to meet the same challenge, make perfect sense under Darwinism. Under Design they would be whimsical, "just because". Why keep reinventing the wheel, over and over again, and why make it clearly different in detail each time, with structures often obviously improvised from earlier structures? Or why come up two different solutions when one seems to work well enough?
