* Since the development of the modern synthesis of evolutionary science, researchers have been working hard to obtain more evidence and nail down details. Paleontologists have made a long string of significant discoveries, particularly in obtaining an increasingly detailed picture of the evolution of the human species. Theoreticians haven't been idle, either, working to assess the importance of neutral mutations in evolution, and coming to the ingenious realization that evolution by natural selection is a competition between "selfish genes" that are trying to out-replicate each other.
* The discoveries of prehuman fossils by Dubois, Dart, and Broom in the prewar era accelerated in the postwar era, particularly through the work of a white Kenyan named Louis B. Leakey (1903:1972) and his wife, Mary Leakey (1913:1996). In 1959 the Leakeys discovered another variety of "robust" australopithecine in Kenya, and in 1961 they discovered a very different hominid, which became known as Homo habilus. By this time the consensus was emerging that the australopithecines were a side-branch of human evolution that went extinct; Homo habilus, in contrast, was closer to the main line of human evolution, roughly a predecessor to Homo erectus. It appeared that australopithecines and Homo habilus lived side-by-side.
More discoveries cropped up to bolster these concepts. In the mid-1970s, a surprisingly (if by no means perfectly) complete skeleton of an early australopithecine was discovered in Ethiopia, with the specimen named "Lucy". It confirmed much of what had been believed about the australopithecines, in particular that they walked erect. Louis and Mary Leakey's son Richard Leakey (1944:2022) also discovered a number of hominid fossils, in particular helping confirm the past existence of Homo habilus.
Older hominid fossils were discovered in the 1990s that traced the existence of the hominid branch of the primate evolutionary tree farther back in time. There are now hundreds of hominid fossils for australopithecines, Homo habilus, and Homo erectus, and neither their reality nor their testimony to the antiquity and evolution of the human species can be realistically denied any longer. The exact arrangement of the hominid family tree does remain open to debate, and in the absence of hard genetic evidence that can't be obtained from such fossils, the argument will be difficult to resolve. However, as is true in general for disputes in modern evolutionary science, this is merely fussing over details.
BACK_TO_TOP* With the development of the modern synthesis and the discovery of the genetic code, evolutionary science entered a new era. The emerging science of what would be called "genomics" promised to give evolutionary biologists a microscope into the organization of organisms and the relationships of species. An American biologist named Richard C. Lewontin (1929:2021), a student of Theodosius Dobzhansky, was a pioneer in this effort, using a technique known as "gel electrophoresis" to perform genomic studies. He discovered that the genetic variability even among the same species was much greater than anyone had anticipated.
This discovery meshed neatly with the work of a Japanese population geneticist, Moto-oh Kimura (1924:1994), who in 1968 began to argue that evolution was heavily driven by "neutral" mutations that neither harmed nor helped an organism -- they were "selectively equivalent". The idea was not all that new in itself, there was no reason for anyone but the strictest selectionist to reject the idea that a species might undergo changes that did neither harm nor good -- but Kimura came up with a detailed model of how it might work, showing how genetic drift could accumulate variability in a species that, when new selection pressures arose, would provide a basis for new adaptations.
Kimura's "neutral theory" was at first interpreted as an attack on the Modern Synthesis, but Kimura was careful to point out that it contradicted nothing in basic evolutionary concepts: "The theory does not deny the role of natural selection in determining the course of adaptive evolution." In fact, Darwin himself had briefly mentioned the idea early in chapter four of THE ORIGIN OF THE SPECIES: "Variations neither useful nor injurious would not be affected by natural selection and would be left a fluctuating element ... "
Kimura's ideas were a further extension of the earlier work of Sewall Wright, in essence claiming that the movement of the evobot over the fitness landscape was more drunken and unsteady than had been previously assumed. Where Kimura was controversial was in his claim that neutral variation was more important in evolution than natural selection.
Kimura's work focused on neutral variations at the genetic level, a notion that is thoroughly rooted in the evidence. As discussed later, a complicated biomolecule common among a set of organisms, identical in function in all those organisms, will inevitably have variation in structure due to neutral mutations in the gene that produces it -- with an analysis of these neutral variations coming in handy for providing information on the evolutionary history of these organisms. Such neutral variations by definition would have no effect on the structure or behavior of an organism, but they would provide increased genetic diversity that could feed evolutionary change in the future.
Others suggested that the neutral theory applied at higher levels as well. Harvard paleontologist Stephen Jay Gould (1941:2002) criticized the notion that all features of organisms were necessarily purposeful, created by natural selection. Why, for instance, are bobcats and lynxes the only wild cats with stubby tails? Their lifestyles aren't so different from those of other wild cats to think there was much advantage in a stubby tail. Many features of organisms, as Gould saw it, were merely accidental, or incidental consequence of adaptations, and provided neither selective advantage nor disadvantage in themselves. In Gould's view, since evolution was an undirected process, driven by random genetic variation, then it would be unsurprising, even expected, for organisms to acquire seemingly whimsical features -- or at the very least, a wide variation in features, where one version was functionally about as effective as the others.
Gould referred to explanations to show how every little feature of an organism was derived from natural selection as "just so" stories, referring back to Rudyard Kipling's fables for children of how the elephant got its snout and so on. His critics warned against complacency, responding with stories of how various adaptations of organisms that had once been dismissed as irrelevant turned out to be "anything but", and pointed out that over the generations evolution amplified even faint selective advantages.
Still, although the debate between neutralists such as Gould and strict selectionists -- or "adaptationists" as Gould called them -- got a bit hot at times, the argument was never really over the fundamentals of evolutionary theory itself. It was simply arguing over the "glass half full" versus the "glass half empty". Given that evolution isn't a guided process, the question of: WHY? -- relative to the features of organisms, is inevitably mirrored by the question of: WHY NOT?
Nobody denied that evolution involved both random variations and selected adaptations; it was just a question of how much weight was put on the two processes, and nobody could deny that selection was the ultimate arbiter of what features were workable -- not necessarily advantageous, just not troublesome -- and those which were unworkable. In fact, trying to establish the dividing line between the two was tricky, since neutral variations in organisms could, when conditions changed, provide a basis for new selected adaptations.
Indeed, more recent thinking suggests that an organism might well accumulate a series of neutral variations, none having any real effect -- until a variation is acquired that renders the series functional, giving the impression of a complex feature acquired all at once. Experiments suggest that such "constructive neutral evolution" can occur, though the matter remains under discussion. As far as Kimura goes, the contemporary mindset is that he may have overstated his case, but he was certainly not entirely wrong.
BACK_TO_TOP* While Kimura was working towards his neutral theory, in 1964 a British graduate student named William D. Hamilton (1936:2000) published a significant paper titled "The Genetical Evolution Of Social Behavior" that advanced the work of Ronald Fisher, Hamilton's hero, to explain the origins of altruism.
The concept of self-sacrifice had never made much sense in classical evolutionary theory, but it was perfectly evident in the conduct of both humans and animals. The stinger a bee is generally torn out when used against an enemy of the hive, sacrificing its life for the protection of the hive. Anyone who wanders past a prairie-dog colony will hear sharp "barks" (actually, they sound like chirps) as individual prairie dogs stand up and give warning of an intruder to the other members of the community -- even though the barks draw unwanted attention from potential "hostiles".
A general idea arose that altruism was a product of "group selection". Consider, say, sets of prairie dog colonies in competition with each other. Suppose, at some time in the past, prairie dogs didn't bark to alert each other of the approach of predators. If the members of one colony acquired an inclination to give warning to other members of the group, the colony would obtain a selective advantage that would allow it to grow faster than competing colonies, even if it meant sacrificing a few individuals among the colony. That colony would then become dominant over others.
The problem with the idea of group selection was that, while it sounded very plausible in a "big picture" sort of way, it didn't make sense in terms of the mechanisms of evolution as they were understood. Individual prairie dogs are not merely in competition with predators and rival species; they are in competition with other individual prairie dogs -- in fact, the other prairie dogs are the closest rival competitors, inhabiting the same environment, eating the same foods, and after the same mates. In evolutionary terms, it would seem that a prairie dog should have no reason to encourage the advancement of its fellows at any expense to itself.
If prairie dogs with a genetic inclination to give warning were more vulnerable to predators, even if only slightly, then over time natural selection would gradually eliminate them, leaving behind prairie dogs with no genetic inclination to give warning. Why, then, did altruism persist? If nice guys finish last in the evolutionary race, they should have been weeded out. How could literally mindless natural selection accommodate a concept such as altruism that seemed to involve the ability to see the "bigger picture"?
Darwin was aware of this difficulty and had speculated on the issue, but he was never able to accommodate it in his theory in a very clean way. There was a frustrating gap between the notion of group selection, which seemed so obvious on the surface, and the machinery of how things worked. Hamilton's solution was to propose that natural selection was not between organisms, but between genes.
The notion that evolution is only really about genes sounds silly, along the lines of the notion of "a hen is an egg's way of making another egg." Hamilton himself worried that maybe he sounded like a crank. However, as he pointed out, if natural selection is all about the competition between sets of genes to propagate, then altruism is perfectly logical: the sacrifice of a few organisms to protect others carrying the same genes would ensure the propagation of genes that programmed an inclination towards altruism.
Suppose that prairie dogs could reproduce asexually, and an individual prairie dog colony consisted of females who gave birth to female clones. In that case, then the sacrifice of a few individuals would aid the propagation of the rest of the colony with the same genetic inclination towards altruism. Of course this is a far-fetched scenario, asexual reproduction never having been reliably observed in mammals, but it can be easily adjusted to reality by realizing the obvious fact that organisms share part of their genomes with kin.
Identical twins are clones and share their full variable genetic complement; other siblings, on the average, share half; half-siblings, a quarter; cousins, an eighth; and so on. Notice the important use of the term "variable complement": the majority of genes are identical among members of a species -- in fact, there are genes that are common to a lesser or greater extent among all living species -- but in terms of intraspecies competition it's only the genes that are variable among the members of the species, the alleles of "polymorphic" genes, that are important.
Hamilton put together a model to show how this worked: "In the world of our model organisms, we expect to find that no one is prepared to sacrifice his life for a single person, but everyone will sacrifice it when he can thereby save more than two brothers, or four half brothers, or eight first cousins." In all three cases that Hamilton cited, the odds were that the sacrifice would propagate the particular set of genes. If a prairie dog raised his own probability of being eaten by barking a warning, the members of his common gene pool were safer as a result, with that gene pool being carried down.
Similar concepts were put forward in much more detail by an American evolutionary biologist, George C. Williams (1926:2010), in his 1966 book ADAPTATION & NATURAL SELECTION. A contemporary British evolutionary biologist, John Maynard Smith (1920:2004), came up with the concept of "kin selection" as a less preposterous-sounding alternative to gene selection.
BACK_TO_TOP* Not everyone was enthusiastic about the notion that natural selection operated at the level of the gene, and in fact Ernst Mayr would denounce the idea to the end of his considerable number of days. Part of the reason for the lack of general acceptance was that neither Hamilton nor Williams were particularly sparkling in their ability to communicate their ideas. However, the concept of gene selection acquired a disciple, an Africa-born Briton named Richard Dawkins (born 1941), who had studied under well-known animal behaviorist and Nobelist Niko Tinbergen (1907:1988) at Oxford. Dawkins, an excellent writer, absorbed Williams' ADAPTATION & NATURAL SELECTION and made it accessible to a popular audience through his first book, THE SELFISH GENE, published in 1976.
THE SELFISH GENE elaborated in detail on the notion of selection operating at the level of the gene. The title was somewhat sensationalistic, and Dawkins later admitted that it had some drawbacks. Creationists, in their eagerness to find stones to throw at MET, grabbed on to the title, ignoring what Dawkins sarcastically called the mere "footnote of the book itself" to proclaim that Dawkins was promoting some sort of Social Darwinist concept that said selfishness was okay. The truth was, as Dawkins put it, the book devoted "more attention to altruism." He conceded that THE CO-OPERATIVE GENE would have been more appropriate, if not as catchy.
As Dawkins described it, the notion of gene selection was a logical outgrowth of the Modern Synthesis. Evolutionary theory had always seen the emergence of species as due to random changes in replicating entities, selected in a competition for survival. But what were the actual replicating entities, or "replicators" as Dawkins put it? The obvious answer was that it was organisms that replicated. However, if replication is defined as "making a copy of oneself", then strictly speaking the organism itself doesn't replicate. If an animal loses an eye or leg through an injury, its offspring will still be born with a full set of eyes and legs. If true copies were being made, for example with some sort of sci-fi "matter replicator", they would all look the same, still missing a leg or an eye. The notion of the organism being the replicator had basically fallen to ruin along with Lamarckism.
In reproduction, what happened was that an organism created a copy of its genome, which then constructed a new organism. From this point of view, the organism was just a "survival vehicle" for the genome. Even this idea was questionable in that the evolution of a replicating entity implied a specific identifiable entity -- while a genome, at least in normal sexual reproduction, was completely scrambled through recombination from generation to generation. The actual entities were the genes that made up the genome, with each genome amounting to a "team" of genes directing the construction and operation of an organism, a survival machine. Genes did not serve the organism; the organism served the genes.
The notion sounds arcane, but makes more sense if the sterile drone workers and warriors of hive insects are considered. The drones don't reproduce and have no future, but they serve as tools to help propagate the gene line of the hive as carried in the hive queen. They can be thought of as "drones" in the military sense of expendable remote units.
In evolutionary competition, a gene was driven to make copies of itself. That was essentially its "purpose in life", and it's obvious as to why. Anticapitalists sometimes complain about the fact that businesses have the profit motive as a top priority, but that is necessarily so, since if they don't make a profit, they go out of business and become extinct. Similarly, a gene must successfully keep on making copies of itself, or it dies out -- the logic is so direct that it almost sounds like circular reasoning, but it's more of an "iron law": If we don't make a profit, we go out of business.
Dawkins elaborated on this notion to show how the "selfish gene" led to the emergence of altruism in organisms for the purpose of ensuring the replication of genes. He leaned heavily on the concept of an "evolutionarily stable strategy (ESS)", devised by Maynard Smith. An ESS is a way to describe behaviors, including altruistic behavior, that ensure gene line propagation. An ESS can be thought of as a prudent business strategy that provides a payoff for the gene line over the long run; a prairie dog's inclination to give warning turns out to be an ESS.
The objection has been raised that a prairie dog has no way of calculating the balance between its altruistic risk and the degree of relatedness of other prairie dogs being warned, but like so much else in evolution it doesn't need to be that precise. A prairie dog is a member of an immediate family group and the colony is an extended family group; it's not hard to see where the prairie dog's loyalties lie. Of course, under this model adoption is not an ESS, since it involves organisms investing effort in offspring that don't share their genes, and amounts to a "misfiring" of the evolutionary altruistic instinct -- but adoption's so infrequent in the animal world that it doesn't have a real impact.
Dawkins elaborated on the theme of the ESS in detail in THE SELFISH GENE, showing how such strategies arose in sexual competition, child-bearing, social structures, parasitism, symbiosis, and so on. The variations could become thoroughly baroque and sometimes hard to thread out. Even on close examination, the notion of gene selection seemed a bit strange, but as Dawkins showed, it was only gene selection that made it possible to make sense of things like altruism in the framework of evolution.
* Criticisms were raised against the "selfish gene" concept, in that individual genes can't really accomplish much on their own. It is a oversimplified idea to think of MET envisioning organisms undergoing a mutation, with that mutation then screened by selection, with another mutation arising and then being screened in turn. In reality, the observable features of organisms typically are produced by the interactive effects of a set of genes, and it's such expressed features, not the genes that produce them, that actually determine how well the organism stacks up in evolutionary competition. The interactions between genes can be extremely complicated and subtle, with the effects of a change in any one of them being often hard to detect.
Dawkins found such criticisms exasperating because he had carefully articulated that issue from the start, insisting that it was the "teams" of genes making up the genome that determined evolutionary success -- but the scrambling of the genome during sexual reproduction meant that the "team" couldn't be thought of as a fundamental unit. Gene selection was all about teamwork, with "star player" genes advancing their propagation by contributing to the success of the various "teams" they signed up with in the course of sexual recombination through generations. The "loser" genes would, on the other side of the same coin, gradually fade out of the gene pool.
There is an interesting example of genes being bad "team players" that actually ends up demonstrating the rule. In chromosomal crossing-over, the genes on paired chromosomes are mixed in the process of producing a haploid chromosome for a gamete. This ensures that the odds of one or another allele of the same gene being used in the gamete are about 50:50. In other words, crossing-over ensures "fairness" in gene propagation. However, if evolution is at the gene level, then a particular gene would seem to obtain an advantage by acquiring means to "cheat" and encourage its own propagation at the expense of its allele.
Sometimes genes do cheat, stumbling onto mechanisms that encourage their propagation at the expense of an allele. The phenomenon, known as "meiotic drive" or "segregation distortion", was first observed in some Drosophila fruitflies in the 1950s. But since the "selfish gene" theory says genes have a built-in predisposition to promote their own propagation, then why isn't it the norm? If the gene cheats, it will propagate rapidly through a population, and it would seem likely to take over completely.
The catch is that, by eliminating its allele, the cheating gene has undermined genetic diversity in the population of hosts, in effect forcing inbreeding, which is by the odds not likely to be healthy for the hosts. In other words, a gene that is likely to cheat does not have an ESS, since it tends to drive its hosts to extinction and itself along with it. As is characteristic of evolution, meiotic drive continues to arise, over and over again, as mutations give specific genes the ability to cheat -- but the cheaters will be always be trimmed back, sooner or later, by the Grim Reaper and will never get the upper hand.
As Dawkins once pointed out, there is not only an evolutionary competition between organisms, there is an evolutionary competition at a low level within organisms as well. The reason that the internal systems of organisms are as a rule very well balanced is because the strategies of cheaters that undermine this balance have a very strong tendency to be dead ends: a cancer cell is a cheater, replicating without restraint until it simply kills off its host and itself along with the host. Although cheating genes aren't as malign as cancer cells, they are just as self-defeating over the long run. Chromosomal crossing-over is not a product of some ideal of "fairness", it exists because the "team" in which one of the "players" becomes a prima donna is ultimately the losing "team", and selection pressures force it out of business. As Dawkins put it: nice guys finish first.
Incidentally, genes that promote their own propagation at the expense of their alleles were traditionally known as "selfish genes", with other genes being implicitly "unselfish". Dawkins' use of the term "selfish gene" in a more general sense was a break with tradition, and there was some annoyance with his expanded interpretation of the concept.
BACK_TO_TOP* THE SELFISH GENE also introduced the concept of the "meme", a word Dawkins himself coined, though the notion itself was not entirely new. The meme was a simple idea. Through much of evolutionary history, species had evolved through natural selection, acquiring capabilities "hardwired" into their genomes and passing them on to their progeny. However, as animals grew more intelligent, they were increasingly capable of not merely learning, but also of teaching their learning to their children, giving them capabilities that were not hardwired into their genes.
These elements of knowledge were what Dawkins identified as "memes". Purely instinctive creatures, such as insects, had no memes, their actions being completely directed by their genes. Smarter creatures can learn from their actions and teach by example. Of course, the process reached an explosive level in humans; evolution had finally transcended mere "hardware", the propagation of genes, and now involved "software", the transmission of memes through writings, songs, oral narratives, physical training, computer programs, and so on. Dawkins insisted that memes were every bit as real as genes. A gene, after all, is no more than a coded message, implemented in DNA to be put into operation. A meme is similarly a coded message, implemented in the synapses of the brain to be put into operation. Memes could evolve through competition.
In Dawkins' view, memes gave humans some ability to transcend "the tyranny of the gene". Although altruism in his view had originated from the dictates of the "selfish gene", human ethics had transcended its roots: for example, humans adopt children all the time, without concern for the specific sharing of whatever proportions of genes. Dawkins was absolutely no Social Darwinist, he was not claiming that the imperatives of biology amounted to moral law. Was adoption an ESS? No, it clearly wasn't -- but so what? Any couple that adopts children knows perfectly well that adoption won't propagate the couple's gene line. Few would find it sensible to raise an objection to adoption on this basis, nor argue that it was a good reason to discourage the practice. As has been said: "Our genes can take a hike."
Dawkins emphasized that his point was that if humans aspired to a higher morality, they might not find their genetics were always helpful to that end. In this he was expressing the ancient belief that our "better angels" of our nature were locked in tension with our bestial instincts. Dawkins went further, suggesting that memes might actually win this battle over the long run.
It is often claimed that humans, more or less buffered from natural selection by their technology and social systems, have ceased to evolve, but if the evolution of memes is factored in, human evolution is moving along at a breakneck and accelerating pace. Dawkins speculated that in time humans are likely to develop intelligent machines, and then a meme-based path of evolution will have arisen, with the intelligent machines building ever more intelligent machine progeny. Whether this would be a beneficial thing or not from our point of view is of course another good question.
* There was some controversy over the concept of a meme, with some doubters suggesting that the idea was, if not wrong as such, too vaporous to be useful, amounting to mere "hand-waving" that didn't actually deliver anything of substance. However, this controversy was nothing compared to the one that Dawkins provoked when he pushed notions that sounded like genetic determinism on a heavy dose of recreational drugs: "We are survival machines -- robot vehicles blindly programmed to preserve the selfish molecules known as genes. This is a truth that still fills me with astonishment."
Critics predictably blasted Dawkins, accusing him of a coldly mechanistic vision of humanity -- some of his readers said that THE SELFISH GENE threw them into a profound depression. Those more familiar with Dawkins wondered what the fuss was about, finding it hard to believe that he saw the notion of "survival machines" as anything but an evolutionary abstraction. No reader of Dawkins' books on science would get the impression that he was lacking in self-esteem and took such a bleak view of himself, and his readers also know he has a tendency to throw bombs, expressing ideas in a provocative fashion to get the reader's attention, and then adding qualifications to bring them back down to earth. This is one of the reasons he's an interesting read, though unsurprisingly it causes him difficulties every now and then, forcing him to backtrack a bit.
In fact, he later found his remark about "survival machines" something of an embarrassment, saying that he wrote it in a burst of excitement after coming back from a "mind-boggling" conference on artificial intelligence research, and though he didn't retract the statement, he went to considerable lengths to clarify it. What Dawkins meant was that the evolution of genes, with some propagating and others dying out, is entirely blind, mechanistic, and robot-like. Genes don't plan out strategies; they're no more conscious than a brick, they can't plan out anything. They are handed game options in the evolutionary lottery by blind random mutations, to then suffer through the contest imposed by equally blind selection pressures, with some genes proving winners and propagating while the losers fade away.
Dawkins didn't mean that humans were robots under the uncontestable control of genetic instructions, as if they had brain-control chips implanted in their heads. He was not happy to find out that the cover of the German edition of THE SELFISH GENE displayed a puppet on strings, while the French edition had little men in bowler hats, each with a windup key on his back.
* There was really little valid reason to get upset over the notions of "selfish genes" and "survival machines". They made a good deal of sense in terms of evolutionary modeling, but it's hard to think that anyone could usefully apply such notions very far outside of that domain, any more than a socket wrench is useful for baking a cake -- a scientific theory can only at best explain what it was created to explain. Even Dawkins was perfectly willing to still present evolutionary scenarios as selection between organisms and leave gene selection as implied: "Just as it is not convenient to talk about quanta and fundamental particles when we discuss the workings of a car, so it is often tedious and unnecessary to keep dragging genes in when we discuss the behavior of survival machines."
Some biologists felt it was just as convenient at times to consider selection at higher levels, with Stephen Jay Gould suggesting that it applied at levels up to that of the species. Advocates of group selection demonstrated that there was no inherent conflict between it and gene selection. Purists didn't claim that such notions were completely wrong but argued that they could be misleading, as demonstrated by dubious concepts of group selection that show up in the popular literature every now and then.
This was all clearly a debate within the scientific community and of no great interest to the general public. There was no real cause for public controversy over the "selfish gene". However, Dawkins' comments about the evolutionary basis for behavior contributed to an unending feud.
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