v1.2.2 / chapter 14 of 28 / 01 aug 08 / greg goebel / public domain
* One of the primary objections to Darwinism is that unguided natural selection couldn't have produced complicated biosystems. According to this line of thinking, it may be able to produce minor changes, such as antibiotic resistance -- "microevolution" -- but it can't produce elaborate biostructures -- "macroevolution". On investigation, the obstacles to the idea of macroevolution evaporate.
* A few critics of Darwinism claim the mutations that produce antibiotic resistance and so on were too improbable to have happened by accident and had to have occurred by Design. Their calculations are disputed, not supported by lab studies, and many critics are willing to concede that the idea that, say, alien white mice are mysteriously tweaking the genomes of various organisms amounts to excess baggage -- all the more so because the emergence of antibiotic resistance, sooner or later, is effectively predictable and guaranteed. The evolutionary battle between parasite and host has been going on for a long time and is in obvious evidence.
However, the critics call such examples "microevolution". They feel it is a jump to think that Darwinism could account for all the elaborations of forms cited by the Reverend Paley, such as the creation of the eye, or in other words "macroevolution". There are those who simply refuse to believe it, claiming that microevolution and macroevolution are categorically different, and deny that macroevolution is possible. Elaborate features of organisms, they insist, could have only happened through a miracle of supernatural intervention -- Design.
Macroevolution does present a conceptual challenge to Darwinism. Richard Dawkins wrote a book titled THE BLIND WATCHMAKER to consider the plausibility of Darwinism, and in its pages he pointed out bats as an example of such a seeming Design elaboration. Many (though not all) bats rely on sonar for navigation, in which a sound is emitted and its echo then timed to range and identify an object. Radar works on the same general concept, though it uses radio waves instead of sound. The interesting thing is that bat sonar has so many technical similarities to human radar.
For example, if a jet fighter is operating a radar to search the sky for an opponent, it sends out radio pulses on a fairly long interval -- what radar engineers call a low "pulse repetition frequency (PRF)". This allows a pulse to go a long ways before a second pulse is sent out, giving the radar more range. If a target is identified at attack range, the PRF jumps up drastically, allowing the target to be tracked closely. The common brown bat Myotis will chirp at a rate of about 10 times per second when searching for insects, but this rate will go to 200 times a second when an insect is spotted.
Similarly, a radar usually has a single antenna for both transmit and receive. Since the radio echo is faint, the receiver needs to be sensitive and the powerful transmit pulse will tend to fry it. The trick is to use a "diplexer" that shuts off the antenna receiver path while the transmit pulse is being sent. The Myotis bat has sensitive ears to pick up its ultrasonic chirps; a special bone mechanism shuts down the ear channels while a chirp is being emitted so the bat won't deafen itself. The Myotis bat even has a ability that nobody clearly understands to sort out echoes of its own "voice" from those of others -- the bats tend to live in colonies, sometimes dense ones, and have no problem navigating in the dark when dozens of other bats are in flight nearby and are filling the darkness with their chirps.
Is it even possible to imagine that something as sophisticated as bat sonar could arise by Darwinian natural selection? If everyone admits that an organism gives an impression of having been Designed, isn't is pigheadedly overlooking the obvious to then claim it wasn't? How could it be the result of anything but a specified plan? Dawkins indignantly denies the charge of the critics that Darwinism is a "chance" process, but what the critics clearly mean by "chance" is that under Darwinism nothing has been created by a blueprint, from some carefully predefined specification. This is precisely what Dawkins wrote THE BLIND WATCHMAKER to prove.
* On a superficial examination, Darwinian macroevolution seems preposterous, and no sensible person would fail to give it a skeptical looking-over. Many critics of Darwinism insist that it is impossible and have proposed explanations of why. One common tale presented in a number of variations to illustrate the gulf between microevolution and macroevolution is the "canyon" story.
The premise is that there is a deep, impassible canyon -- representing an evolutionary jump -- between a woman named Alice and a neighbor named Bob. If the canyon is very narrow, Alice can simply jump across (microevolution). Now suppose that the canyon is extremely wide (macroevolution). Alice can't just jump across; what Darwinism claims, as the critics have it, is that Alice managed to get across the gap by jumping across a series of mesas in the canyon. It took her a very long time, of course, and the mesas eroded away behind her and left little or no trace, implying the sketchiness of the fossil record. The scenario shows that macroevolution is a ridiculous concept.
It must be emphasized that analogies are useful as illustrations, but they don't constitute proofs of anything in themselves: they are only as valid as their correspondence to reality. In this case, the correspondence is broken because the story conjures the notion of a barrier, an "impassible canyon". In Darwinian terms, this is a contrivance: "Huh? Barrier? What barrier?" Darwinian evolution works one step at a time, moving from one useful adaptation to another, following the line of least resistance over the adaptive landscape. If Alice and Bob are only 100 meters apart (microevolution), Alice can walk over in a few minutes. If the two are 10 kilometers apart (macroevolution), Alice will take substantially longer to walk over and visit Bob. The only distinction real distinction between microevolution and macroevolution is that macroevolution takes more time.
* A similar but even more contrived tale posed by critics considers the possibility of a prairie dog crossing a busy highway. If the highway only has two lanes or four lanes (microevolution), the probability of a prairie dog getting across is reasonable. However, suppose that the highway has a thousand lanes (macroevolution): the prairie dog has zero chance of making it across alive. Macroevolution is now shown to be impossible.
The tale of the prairie dog is interesting because it correspondence to the actual details of how Darwinian evolution works is so muddled that it merely seems absurd. It also is interesting in that revising the story to get rid of the muddle provides a tidy, if cartoonish, example of how Darwinism works. Let's modify the scenario by envisioning a whole colony of prairie dogs on one side of a thousand-lane highway, and adding habitable dividers between the lanes.
Suppose the prairie dogs completely strip the side of the highway they are living on of plant life. They now have a choice of staying where they are and starving, or crossing a lane of the highway to the divider. The colony gradually migrates across the lane, losing a proportion of their number in the process, and sets up home in the divider, raising a new generation. The new generation of prairie dogs strips out the divider; since the side of the highway that their parents came from is still barren of plant life, all they can do if they want to survive is migrate across the next lane.
This process is repeated for a total of a thousand generations, when the prairie dogs finally reach the far side of the highway. In the final crossing, not at all incidentally, the proportion of prairie dogs killed is substantially smaller than the proportion lost in the first crossing: the slow and the stupid were run down over the crossings and eliminated from the gene pool. This is how Darwinism works: whole populations undergo selection pressures over a number of generations. The scenario also parallels reality in that it takes a long time, a thousand years or more, for the prairie dogs to get across, and in the process many "losers" end up being left on the highway. If there was an indefinite number of lanes, sooner or later the descendants of the original prairie dogs would have the skills to cross the lanes without any particular difficulty.
In Darwinian terms, macroevolution is nothing more than microevolution multiplied, a walk between towns versus a walk across the room -- not a climb over some overwhelming obstacle, but a smooth progression, a video of a species slowly "morphing" a generation per frame. There is no more inherent distinction between microevolution and macroevolution than there is between a pebble and a boulder.
To be sure, some evolutionary innovations are of much more far-reaching significance than others -- one of the best examples being the emergence of sexual reproduction, a demonstration of the "evolution of evolution" -- but the fact that some innovations have more impact than others doesn't change the basic argument in the slightest. There is also, as discussed earlier, the possibility that macromutations may occasionally occur in the process, but nobody has been able to show that they must, and even if they do, once again the Darwinian argument remains effectively intact.
* Incidentally, it must be noted that though there is no known "magic barrier" to evolution by natural selection, that's not the same as saying that evolution by natural selection never runs into obstacles. Envision a colony of prairie dogs and a thousand lane highway without dividers. When the prairie dogs strip out the vegetation on their side of the highway, their only choice is to try to cross the highway or starve.
What happens? The answer's obvious: they all die. This is does not present the slightest challenge to Darwinism: extinction happens all the time -- nobody sees velociraptors running around any more except in the movies -- and in fact Darwin himself described extinction as an important background element of his case, since it implied the succession of species. Critics occasionally claim that the failure of a population to adapt to changing conditions disproves Darwinism, but the simple reality is that if the change is too drastic, the fitness landscape too harsh, evolution by natural selection will be too slow to save a species. The species has no means of "willing" the necessary mutations needed for survival, no matter how desperate the circumstances.
The shifting fitness landscape actually can set up barriers, either channeling evolution in particular directions or setting up traps from which there is no avenue of escape. This is demonstrated by the mass extinctions of the past, particularly the Permian extinction, when a very high percentage of species died out. In Darwinism, species can be expected to go down blind alleys and reach dead ends, over and over and over again.
* There is another aspect to the objections to Darwinian macroevolution, in that the critics tend to assume destiny: that a particular complicated system needed to perform a function was a preconceived Design and so the odds of it happening by natural selection processes were vanishingly low. However, under natural selection a range of possible systems might well have arisen to perform the action, and the one that did emerge was only one of the possibilities. Alice wasn't actually planning to walk over to Bob's house, she was just following the path in front of her that seemed easiest with no particular final goal in mind, and Bob's place is where she happened to end up. A critic would proclaim it absurd to think that Alice could have navigated her way to Bob in such a fashion, but that's missing the point: she ended up at Bob's house, she could have just as easily ended up at Zelda's house. The probability that sooner or later Alice was going to end up someplace was, barring misfortunes, one.
The philosopher Daniel C. Dennett (born 1942) expressed much the same idea in terms of a con game. Suppose Bob gets a mailing list of 1,024 gamblers who bet on football matches. He picks an upcoming game between team A and team B, then sends 512 gamblers an email saying team A will win, while sending the other 512 an email saying team B will win. If team A wins, Bob drops the 512 gamblers who got the prediction for team B off his mailing list, picks an upcoming game between team C and team D, then sends 256 gamblers a prediction that team C will win and the other 256 an email that team D will win. If team D wins, Bob drops the 256 gamblers who got the prediction for team C off his mailing list -- and keeps on playing the same game, dropping his list to 128 gamblers, then 64, then 32.
These 32 gamblers have been handed the right call on a football match from Bob five times in a row and think he has a miraculous ability to predict the future. Bob then says he will give the 32 gamblers the results of the next game ... but only if they each pay him big money first. The suckers don't realize that Bob never predicted anything -- they're only seeing one of all the possible "evolutionary sequences" of predictions and don't realize that all the rest were dead ends.
In more general terms, the critics are falling into the "lottery winner fallacy". If somebody wins the big lottery, a critic might just as easily say that since the odds of winning are extremely low, there was no way that the winner could have won by accident: the lottery had to have been rigged by someone. The reality is that somebody wins, it's just impossible to figure out who it will be ahead of time in a fair lottery. Darwinian evolution tends to produce a solution in response to selection pressures, but it produces any solution that works.
* In any case, on close examination, the supposed obstacles to Darwinian macroevolution don't turn out to be as insurmountable as the critics made them out to be. Why can't a thousand microevolution events make up a macroevolution event? If provable small changes can occur over a short period of time -- or maybe even not so small, such as the transition from wolf to pekinese -- what no good reason is there to think that many small changes over a long period of time can't add up to big changes? Even arguing that some of the changes are improbable doesn't shoot down the idea, since what is improbable over a short period of time becomes a certainty over a long period of time. If we didn't age and were indestructible, then we could bet that we would be struck by lighting every rare now and then.
By analogy, languages are known to evolve -- try reading Chaucer. Two separated populations of people speaking the same language will gradually develop different dialects over a period of time. Obviously the two dialects will continue to become more dissimilar over time, through small gradual changes, until they are mutually intelligible and have become distinct "species" of languages. Dutch speakers, for example, generally cannot understand Afrikaans even though both languages share the same primary linguistic roots.
Of course, the evolution of organisms and languages are not the same thing, but they have many similarities -- in particular, languages aren't as a rule "designed" and have many functionally nonsensical features, for example the insistence of many languages on assigning genders to all nouns. The analogy is close enough to pose the question of why there is, must be, some sort of "magic barrier" to the emergence of a different species through a process of gradual mutational change, when nobody could propose any comparable "magic barrier" to the emergence of a new, clearly distinct language through a process of gradual change.
* Critics insist that it is strictly an assumption that a thousand microevolution events add up to a macroevolution event. They add that nobody has observed Darwinian macroevolution in practice, and even insist that modification of wolves into pekinese isn't any sort of evidence because, in principle if not in practice, the two species could still interbreed.
The critics are entirely correct in saying that the "linear extrapolation" of microevolution to macroevolution is an assumption. The idea is open to debate, but that means the critics are obligated to come up with credible arguments as to why it isn't a reasonable inference. So far, they haven't been able to identify any plausible "magic barrier" that sets limits on the amount of change that can be obtained through an accumulation of micromutations. The "magic barrier" is an assumption as well, the difference is that it isn't supported by any evidence.
In fact, on closer examination the entire notion of a "magic barrier" seems fuzzy and poorly defined on the face of it. Where does it occur? Were foxes, coyotes, and wolves produced from a common ancestor through microevolution? Were the dog family and the cat family produced from common ancestors through microevolution? How about the carnivores and the primates? Mammals and reptiles? At which of these levels does microevolution run out of steam, and why?
Is making a fuss over microevolution versus macroevolution any more than a red herring? Does invoking a "magic barrier" serve an instructive purpose in explaining the organization of nature -- or is just an exercise in raising out objections? If it is admitted that natural selection can do part of the job, then it comes across as arbitrary to declare that it stops abruptly at some "magic barrier" invoked at whatever level is convenient for the purpose of the argument: "But that's an example of microevolution, not macroevolution!"
In the extreme, the insistence on a "magic barrier" amounts to a transparent ploy, insisting that small-scale evidence from short-term observations is unconvincing -- and then declaring that there is no "convincing" evidence except direct observations over long timescales for which, conveniently, direct observations are ruled out on the face of it.
As far as the criticism that wolves and pekinese are still the same species goes, evolutionists can turn the criticism around. Wolves and dogs differ genetically only by about 1%; if that much alteration can be obtained from 1% variation, how much alteration could be obtained from, say, 5% variation? The physical variation from wolves to dogs shows just how plastic and life really is. Of course, evolutionists can point out that changes beyond that 1% level would eventually undermine the genetic compatibility of the descendants of wolves and pekinese to the point where they cannot interbreed even in principle. Even Darwin, with his weak comprehension of heredity, understood that the divisions between species are gradual.
* In the absence of any plausible mechanism that sets up a "magic barrier", on the basis of the available evidence, there is no good reason not to accept that the extrapolation of microevolution to macroevolution is a useful approximate description of reality that can be accepted, up to the time when we find a better approximate description of reality. To reject the notion simply because it is an inference is to effectively reject scientific inference in general.
Critics of Darwinism like to make a distinction between "experimental" sciences, such as chemistry, that can be directly supported by lab studies; and what they call "historical" sciences, such as evolutionary science and astronomy, which are based on inferences from evidence about the past. The critics say that the conclusions from "historical" sciences are entirely dependent on interpretation of the evidence -- in effect, the critics are saying that since nobody was there to actually see it happen, then any explanations of what happened are just fictions, and one is as good as the other.
Yes, it is true that it isn't possible to observe examples of Darwinian macroevolution such as the emergence of an eye in "real time", because it would require detailed observation over hundreds of thousands or millions of years. However, to use this as a criticism is on the same level as saying that since we can't duplicate a star in a laboratory, we obviously know nothing about stellar astrophysics. We could say that experiments in particle accelerators and the like are too trivial to be relevant, that we can't watch a star evolve over millions of years, and that observations of countless stars in the current Universe at various phases of their lives don't matter.
The same logic would also insist that geology knows nothing about the origins of a mountain range because we can't actually stand there and watch it happen -- not that we would actually want to observe major abrupt geological changes anyway, since such events are most safely viewed from very far away.
Few mainstream scientists make a distinction between "experimental" and "historical" science, since the dividing line between the two is so faint. We can measure the half-lives of radioactive materials in lab experiments; the half-life curves can then be used by inference to then determine the age of fossils through radioactive dating. If the lab studies are credible, then why aren't the results of radioactive dating? In fact, critics seem perfectly willing to cross the line themselves whenever it is convenient for their own purposes, for example calling into question the validity of lab studies of radioactive half-lives to throw doubt on radioactive dating.
Inference is unavoidable in science -- after all, it's not like we can see an electric field -- and if we threw away inference, there would be very little left. Inference is also perfectly common outside of the sciences: if the police raided the house of a burglar and found stolen goods from a half-dozen homes, would the law be forced to accept the burglar's story that he had just found all those goods, simply because nobody had witnessed him breaking and entering? Taking the rejection of inference to an absurdist extreme implies rejecting the idea that one has a brain. After all, how many people have ever seen their own brain?
* As a response to those who persist in declaring that Darwinian macroevolution is preposterous on the face of it, it can be pointed out that Darwinism isn't really much more preposterous than, and in some respects is conceptually similar to, the notion of free market economics, the idea that commerce tends toward efficient operation even without rigid centralized control. A consumer demand will lead to the emergence of producers to meet the demand; prices will reflect the scarcity of products; and inefficient producers will go broke. In this process, both consumers and producers are basically only concerned with their own interests in economic transactions; neither is seriously concerned with the operation of the system as a whole.
There is a story that during the era of the Soviet Union, there was a belief among some senior Communist officials that there was no conceivable way market economies could be really more efficient than a centrally-planned economy. Clearly, there had to be some secret organization that was really planning things out. They turned out to be mistaken.
* One of Darwinism's key concepts is the notion of a selection process.
Richard Dawkins created a simple and interesting computer simulation that
suggests just how powerful a selection process can be. To simplify the
discussion, consider the name:
CHARLES DARWIN
That string consists of 14 characters, including a space. Suppose a computer
program was written to simply throw together characters and see if the result
matched the name of CHARLES DARWIN. How long would it take to come up with a
winner? Given 26 Roman capital letters and a space character, the number of
possible strings of 14 characters is 27^14 = 1.09E20. Assuming that a
computer could generate and test a million strings a second, on the average a
match would be found only about once in 3.5 million years. For every
character added to the string to be searched for, the time would increase by
a factor of 27.
Dawkins suggested another approach:
This description gives the number of strings, or the number of "progeny" per generation, as a dozen, but it can be any value greater than one, and most modern implementations of this program allow the user to set the number of strings. A trial run of a variant of this program, using a progeny size of a dozen and only providing status output every 50 generations, ran to completion in 3 seconds after 4,318 generations.
This is what is known as a "genetic" algorithm. It is straightforward for a computer to make small changes at random, test them, and quickly converge on the answer. This program is generally known as "Dawkins' weasel program" since he used the text example METHINKS IT IS LIKE A WEASEL, that being a citation from HAMLET that Dawkins used in THE BLIND WATCHMAKER to mock the notion that Darwinism was like claiming that a gang of monkeys pounding on typewriters forever could produce the works of Shakespeare -- the "monkeys & typewriters" scenario -- which actually can be loosely regarded as a model of saltationism. A "monkeys & typewriters" or "saltationist" program written along such lines would simply keep generating strings of 14 random characters until a match occurred, which as shown might take a very long time.
* The weasel program is flatly a toy, one that any amateur programmer with an ordinary level of skill could put together in a few hours, but the US National Aeronautics & Space Administration (NASA) wrote a more sophisticated genetic program to determine the optimum design for a small radio antenna, ending up with a piece of bent wire that looked like something a hopelessly bored schoolkid in a dull class would make out of a big paper clip. One of the interesting things about genetic algorithms, incidentally, is that they can actually produce results that nobody envisioned.
It must be emphasized that such programs are not really models of Darwinism as such. Dawkins has been loudly criticised, sometimes in labored detail, because the weasel program demonstrates an artificial selection process, with a specified end goal that Darwinism says doesn't exist. Actually, Dawkins pointed this out to begin with, saying the program was "misleading in important ways ... evolution has no long-term goal ... there is no long-distance target." The program would be a closer representation of Darwinism if, instead of hunting for a fixed string like CHARLES DARWIN, it followed rules of language to create some arbitrary string of text that made sense. However, such a program would be very difficult to write, and from the point of view of what Dawkins was trying to show, a waste of effort anyway.
Dawkins only wrote the program to show what he meant when he said that natural selection isn't a "chance" process. Darwinian evolution, reduced to its bare bones, involves two components, mutation and natural selection. While mutation is indeed a "chance" process, natural selection is not: it is a coldly ruthless process of sorting out the losers from the winners. The end results are so obviously not haphazard or freakish that it is extremely tempting to conclude that the results were specifically Designed in advance, with Dawkins famously speaking of "complicated things that give the appearance of having been Designed for a purpose" and "the illusion of Design".
Darwinian evolution can be compared to a machine, a "Darwin engine", that accepts as inputs random modifications and recombinations of the existing generation of organisms that act as the engine's "memory", and screens those modifications to weed out those that don't work, retaining those that do (or are at least neutral). Over the long run, the engine obtains well-tuned adaptations as outputs, working by a "trial & error" process.
Darwinian evolution is based on chance mutations, but the mutations are screened by a selection process that has very little to do with chance. The rolls of the dice are random, but there is no way to cheat on the process of selecting of winners. What works better wins, what works more poorly loses and dies out, and the process is so blindly merciless that it is impossible to trick it. One critic protested: "Evolution attributes intelligence, the power of choice, to a fundamentally irrational process, namely, natural selection. But nature has no power to choose." On the contrary, nature has the ultimate power to choose: the power to choose survival or extinction. There is no cheating the Grim Reaper.
It might be said that natural selection picks a signal out of the noise of random mutation -- or, much more accurately, it shapes a signal out of the noisy "raw material" of mutations and recombinations as a reflection of the "template" of environmental selection pressures. This is how a process like Darwinian evolution can actually come up with something new and useful without any capability for imagination: try variations at random and then select those that work. The scheme is so unavoidably simple that, as Dawkins has suggested, if we ever found life on another planet, it would as a good bet have evolved by natural selection.
The weasel program demonstrates very clearly what it was built to demonstrate, that it is not unreasonable to think that a selection process can generate large-scale changes with surprising efficiency. Dawkins' weasel program has the virtue of having a simple goal: it provides an easily grasped visualization of how a selection process actually works, in order to shine light on the flaw in the logic of the popular "monkeys & typewriters" misconception. The "monkeys & typewriters" scenario depicts Darwinian evolution as trying to climb up a greased pole; the weasel program suggests it's much more like as walking up a flight of stairs. The weasel program is not so much a proof as a clever and enlightening educational toy.
Not at all incidentally, the "monkeys & typewriters" argument is one of the more common objections to Darwinism, and like the similarly popular "magic barrier" argument, it is expressed in a great variety of ways. Once the "monkeys & typewriters" argument is recognized for what it is, the answer's simple: Darwin never claimed things worked that way.
* As a footnote to Dawkins' weasel program, some have also claimed that it proves Design in evolution, since it is a computer program created by a Designer. This assertion sounds logical for about three seconds, until the realization sets in that it's confusing a model with the thing it's supposed to represent -- like claiming that because a robot toy panda is made in a factory in China, a real panda is made in a factory in China as well. The logic is actually much like that of the old cartoon gag of painting a tunnel into a mountainside and have a train come out. This line of (mis)reasoning is sometimes called the "Gish fallacy" after one of its prominent advocates, a critic named Duane Gish (born 1921), though it's unclear if he actually "invented" it.
Dawkins' weasel program is just a simulation, and a deliberately abstract, simple one at that -- in fact, so simple that some claim it doesn't really qualify as a true genetic algorithm. Simulations only reflect the information that was put into them; it is possible to write a simulation of, say, tornado or planetary orbits, but tornados and planetary orbits are easily explained by the known laws of nature -- nobody believes the old notion that planets are pushed along their paths by angels any more. It can be claimed without contradiction by the facts that the entire Universe is maybe something like a computer program written by some higher power, but that amounts to no more than a premise for a sci-fi story -- "By the Great Programmer!" -- or the theology of UFO cult.
Of course, on the other side of the coin, the fact that computer simulations are artificial models of the real world demonstrates their unavoidable, acknowledged limitation: once again, no model of the real world is any more valid than the assumptions on which it is based, and the conformance of its results to observations.
Dawkins' toy weasel program suggests, as Dawkins himself pointed out, that more elaborate programs could be written along the same lines, simulating an entire ecosystem and the creatures in it, to provide a more accurate model of Darwinism. Following Dawkins' weasel program, work has been done to write "artificial life" computer programs to such an end -- but this is a far more ambitious goal than that chosen by Dawkins, possibly excessively ambitious. Critics question how relevant they are or ever will be, one of the critics suggesting that artificial life programs are no more alive than a Barbie doll is a real woman. Work on such exercises continues.
