By Michael Albert

Each reader of this book incorporates roughly 10 trillion cells of over 200 varieties. Millions of species maintain themselves in endlessly diverse ways. In a thousand years, not all the collective brilliance on the planet could construct a human eye from inanimate components with inanimate tools. Life, even just part of it, is that complex.

From a primordial soup of diverse chemicals, to bacteria, to rabbits to us--how do most scientists explain the transition? Their answer has been, of course, that "survival of the fittest" in natural struggle yields diversity and complexity via mutation, competition, and selection.

Yet recently, out of sight of most of us, a major change of mind has been brewing. Many biologists no longer unanimously accept the basic tenets of Darwinism as the best explanation of the "origin of species." In two articles on evolution, "Salient Science" will address these issues. Here I describe the theory of natural selection as currently supported by its most informed advocates and its most celebrated detractors. In a future issue, I will discuss new approaches to evolution that entirely reject competition and natural selection and discuss some implications of the whole debate and theory.

Such issues are important in part for understanding the natural order and our place in it, and in part for the metaphors that understandings of evolution impart to how we look at all of biology and even social science. Up till now, the evolutionary metaphor informing much common sense about biology and even humanity has been that a brutal, ignorant nature works by a violent struggle in which "only the strong survive." In the new alternative evolutionary theory, however, instead suggests a harmonious and wise nature in which cooperation and ingenuity engender success and aggression is an aberration.

To illuminate the contemporary debate and especially understand why some modern biologists entirely reject Darwinism, we should first hear Darwinists and neo-Darwinists present their case as they themselves see it.

 

Gradualism

Darwin sought to explain fantastically complex biological traits without postulating a divine designer. As the famed zoologist Richard Dawkins suggests, it was like finding a watch on the beach and explaining its existence without invoking an intelligent watch<->maker. All the watch's parts couldn't have accidentally congealed in just the right fashion to tell time. Such an event was too improbable. Likewise, the "human eye could not have evolved in a single jump or just a few jumps," because "jumps that size don't yield useful outcomes." Like watches only more so, live organisms are too complex to arise whole.

Suppose you take a fledgling organism or "eyelet," and make big changes via a random large jump in its components. As Dawkins explains, given the nearly infinite range of possible outcomes, you would be astronomically more likely to get garbage than some useful refinement. Take a car and impose a random redistribution of all its parts and the car isn't going to become a better vehicle. Take the same car and make a million copies, each with a tiny random alteration of just a little part, and a few of the altered cars will likely operate a little better in city traffic. Substitute a biological organ or organism for the car and you have the basis of possible useful changes that could underlie underlie evolution. In short, something just a little better can occasionally emerge from tiny changes in a precursor.

But to get from eyelets all the way to eyes, you need more than "something just a little better." With Dawkins, we must ask: "Could a string of states of eyedom from none to ours exist so that a small jump would take us step by step from beginning to end?" Can mini-steps hang together into a superfine chain of change from ameobas to worms to humans? Earth's geological history spans four billion years. As Nils Eldredge, the Curator of the American Museum of Natural History relates, a mouse that underwent a tiny gradual enlargement imperceptible to human vision in each new generation, would after 12,000 generations requiring only 60,000 years, evolve to elephant size. 60,000 is nearly instantaneous in a span of 4 billion, so apparently little steps can get us a long way, assuming they march steadily in one direction. But that assumption raises a critical question: What force could stretch a chain of small changes into a long trajectory that goes steadily in one direction instead of merely following a twisting path that never gets far from its starting point?

 

Direction

With Gregor Mendel's discoveries, scientists realized that qualities of living things are somehow coded in "genes" which are passed to offspring. Little alterations in the overall gene pool, like those proposed for the car above, occur whenever a gene is accidentally mutated in the offspring as compared to the parent. Then, if the offspring benefits--as when a mutation slightly alters a muscle which makes the offspring a little faster afoot, or slightly alters a chemical balance which causes the offspring to digest food a little more efficiently,--the change will pass on to grand-offspring, and so on.

Still, since mutations are random, why don't traits just meander this way and that? Why doesn't natural history show only a sequence of multi-celled creatures sometimes with one more cell, sometimes one less, sometimes with one facility for processing a neighboring chemical, sometimes with a little different facility? Why do we ever see progressions such as a steady growth in size, increasing ability to fly, or even increasing brain size of our own lineage? Random mutations meander back and forth and cannot generate directed trends unless they are given direction from without. So what imposes direction?

Darwin's answer was that if an offspring has a mutated gene and the ensuing change leaves it better able to leave more progeny than it otherwise would have, those offspring will have the new trait, and they will have more offspring, and so on, until the new trait spreads through the whole population. Then the new organism undergoes further mutation when one offspring has further mutation in the same usefull direction and passes it on, and in this way progression occurs. New traits spread only when they make the offspring better able to survive in the on-going struggle for life.

Darwin takes for granted that each organism always occupies a natural setting, competing with other organisms, foraging for food, and seeking to multiply to the utmost that it is able. Unless restricted by environment, disease, starvation, and\or predators, each organism would expand its numbers forever, eventually overtaking the whole planet with its offspring. Darwin even tells us how two elephants would grow to nearly nineteen million in only 750 years, thereby overflooding the whole planet, if every new elephant lived a full life and had a full complement of baby elephants. He then deduces that since this doesn't occur for elephants or for any other organism, obviously not most organisms that are born do not survive, so that by his definition of fitness, those which do survive must be more fit. So, if a mutation makes an organism's offspring even a little better able to survive--for example, slightly increasing its speed to catch prey or its ability to avoid preditors--that altered creature will do better in the struggle for life and thereby succeed in leaving more offspring than its unmutated siblings. Moreover, its offspring will have the altered gene and in turn also leave more offspring. Organisms without the new trait will be outcompeted, and eventually the mutation will spread to become the norm for the surviving species.

As Darwin himself summarizes his view: "If under changing conditions of life organic beings present individual differences in almost every part of their structure, and this cannot be disputed; if there be, owing to their geometrical rate of increase, a severe struggle for life at some age, season, or year, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of life...it would be a most extraordinary fact if no variations had ever occurred useful to each being's own welfare.... But if variations useful to any organic being do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance, they will tend to produce offspring similarly characterized. This principle of preservation, or the survival of the fittest, I have called Natural Selection."

The conditions the organism confronts establish the "niche" the organism lives in. The organism becomes more or less fit vis-a-vis that niche via a sequence of tiny mutations that each build upon the last and that all increase fitness and are thereby "naturally selected." As the organisms alter, they follows a trajectory of increasing fitness to their niche until they become largely optimized to it. The bat sees in the dark via sophisticated sonor because every mutation from barely being able to hear to distinguishing shapes and motion via the echos of emitted shrill bat whistles was selected for making its host organism more fit. Similarly, a parasitical bug lives successfully in the folds of a snail, getting just the nourishment it needs from the snail's wastes, because its precursors had the relevant traits selected, and likewise for each of millions of types of life.

But if adaptation leads to such a fine fit between species and niches, why doesn't it proceed to this optimization and then stop? Why should the bat or parasite or, more to the point, the earliest bacteria, keep evolving once it is fit?

The natural selectionist's answer is that the environment continually changes so that species continually adapt to the environment's new characteristics. The earth moves and rotates and has huge moving masses of land, and all this motion and change undeniably causes glaciation, alters water levels, shifts altitudes and climates, etc. So, at least over the relevant geological time periods, niches change, and then select for new qualities in the organisms they host. Moreover, beyond climate, a critical part of the environment of any organism is the other organisms in its niche, and they change too.

For example, consider two kinds of animal, one of which feeds on the other. Since both can change, what Dawkins calls an "arms race" can ensue. A particular cheetah's offspring gets a little faster due to an accidental mutation and thus catches gazelles better. The changed cheetah is more fit and has more offspring so the mutation spreads through the cheetah species. Gazelles then exist in a changed environment including a faster predator. A luckily mutated gazelle speeds up, and since it now better escapes faster cheetahs, it survives better than its forebears and passes on its mutation as a new feature of gazelledom, so that now the environment of the cheetah is changed, and the cycle renews. Limits arise because with each new cycle energy that could go to having more offspring, or diversifying the diet, or whatever else that might help fitness, is going solely to increasing speed even though catching gazelles and escaping cheetahs isn't all there is to these animals' "fitness equation." Thus, well before the natural speed limits are reached, speed-up becomes detrimental and the race arrives at a complicated resolution aimed at maximally increasing the spread of each organism's genes.

Moreover, arms races aren't the only way that neighboring genes generate steady evolutionary trends. Genes are selected, remember, not for their intrinsic qualities but by virtue of their interactions with environments. Since an especially important component of a gene's environment is other genes, one possibility is competition, as in arms races, but another is cooperation whereby different genes become steadily better adapted to helping each other persist. Here genes in different living entities support one another, and as each entity changes, new opportunities for enhanced support create a context where the other entity may change. This can foster remarkable symbiosis in a spiral of development similar to an arms race but instead predicated on cooperation. One animal makes use of the excrement of another, or is carried on the wings of another, or is protected by the aura of another, or cleaned by the eating of another, and as each changes so does the environment of the other, in a cooperative spiral. Dawkins points to this cooperation as a source of organs (here living cells presumably play a role similar to symbiotic organisms and the cooperating genes are in one animal's DNA) as well as other symbiotic relations among separate living things.

In both arms races and cooperation trends Dawkins and other scientists provide hypotheses about how evolution yields the results it does. As with any scientific hypothesis, we should evaluate these with the power of our logic as well as by checking the fit between proposed scenarios and what we see in nature--in this case, both now and in the fossil record. Moreover, whichever detailed hypotheses any Darwinian may prefer, all Darwinians agree that chance only provides small random mutations so that the critical ingredient providing all direction in evolution is cumulative natural selection, which is not random at all.

If we now think back to the trajectory from chemical slime to one celled animal, or from fledgling visual perceiver to full blown eye, we can remember the question that the Darwinist had to answer: would each little step in a graded flow from the simple to the complex increase fitness and therefore be selected? The Darwinian's answer, as Dawkins relays it, is "yes." For escaping predators or for finding prey, certainly some perception of light is better than none, 1 percent of an eye is better than just light perception, and 2 percent is better than 1 percent so that the trend, once started, can slowly proceed. The direction taken stems from the impact of the environment which selects for greater vision because greater aids fitness. In a cave, for example, the struggle to survive in the dark selects not light perception, but a steady accrual of ability to perceive the reflection of sounds leading to the bat's sophisticated sonar.

 

Diversity

So far, we have a picture of micro-changes induced by tiny random mutations in genes and selected by changes in fitness of the host animal struggling to survive in a hostile environment. These changes, argues the Darwinist, accumulate into increasing complexity. But where does diversity come from? In particular, why are there so many species, perhaps as many as 2 billion during the lifetime of the planet?

Assuming progressive evolution, Nils Eldredge tells us that "new species can arise in only two ways: by the transformation of an entire population from one state to another (`phyletic evolution') or by the splitting of a lineage (`speciation')." He adds that obviously "the second process must occur: otherwise there would be no increase in the number of [types of organisms] and life would cease as lineages become extinct."

In this light, Dawkins reports that the mainstream Darwinian picture of speciation is that some natural phenomenon divides a largely homogeneous mass of organisms which then goes in separate directions so that two or even three reproductively separate communities of one type of organism emerge. The communities undergo different mutations because they are reproductively separate. Moreover, the reproductively separate communities may move apart, and thereby encounter different selection pressures. If we suppose that the initial organism was a little amphibian, after a million years, two or three divided groups of that creature may evolve into two or three entirely separate organisms.

In traditional Darwinism, speciation is thus "phyletic evolution"--that is, the transformation of the whole population from one state to another--operating more than once on the same organisms divided into separate populations. A population of beetles divides into two reproductively separate populations of the same beetles that occupy different environmental niches, separated, say, by a newly arisen mountain range. Each beetle population evolves as a whole so that in due time each reproductively separated community of beetles yields a new species. Where there was once one beetle species, there arises two. This scenario, repeated ad infinitum, implies that evolution always incorporates a continuous steady trajectory of gradually changing organisms that follow a variety of developmental paths dictated by different niches.

In this view, organisms endlessly shift their characteristics in a steadily graded pattern throughout their existence. The first beetle flows into the next and the next and so on to the mouse, etc., without any specific points along the way where there are sharp divides between beetle type one and beetle type two and between beetles and mice, etc. All is gradual. No natural lines dividing species really exist since there is no change that definitively separates what went before from what followed. There is no species fixity, only change. As Darwin urges: "Natural selection is daily and hourly scrutinizing, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relations to its organic and inorganic conditions of life."

 

Baggage Effect

Some readers may have been wondering, okay, fine, I can see emergence of useful traits and features, but how do innovations which could not have any significant utility for fitness arise, like, say, the human chin? As Elliot Sober the philosopher of science, points out, there never was selection for having a chin. It didn't increase fitness, but it is here anyway. Why?

A plausible explanation of how chins got here is that selection for other features of jaw structure which did progressively increase fitness yielded a chin as an inevitable architectural consequence. As Sober tells us, "Chins may become prevalent because of selection without there being selection for having a chin." The technical name for this kind of evolution is "pleiotropy" and it is very important because it explains the emergence of many existing traits that would otherwise represent problems for the theory of natural selection.

For example, consider the human ability to do calculus. Though calculus has use now, certainly the ability to do calculus didn't imbue early human precursors with increased potentials for reproduction or survival. They weren't calculating areas and bridge spans and the like. Calculus ability wasn't even used and so it could not have been selected as enhancing our forebear's fitness. But calculus ability could have arisen in our forebears as a pleiotropy on logic, or, more plausibly, perhaps both logic and calculus could be pleiotropies on the evolution of language- related capacities. If so, then we would only need to argue that language capacity developed step by step via selection because it increased fitness, and we would get explanations of the emergence of logic and calculus capacities as by-products, a kind of lucky baggage effect, like the chin was a baggage effect of jaw structure.

 

Darwinism

So, ends the familiar, widely accepted Darwinian explanation of evolution. If the picture is true, we should see a "tree of life" with many branches and many attributes being passed on from parent to descendant even as other features become steadily refined and altered or disappear with extinctions. And this is just what we do see. Moreover, as Dawkins says, "if a single, well-verified mammal skull were to turn up in 500 million year old rocks, [before they could have branched off a precursor on the evolutionary tree] our whole modern theory of evolution would be utterly destroyed." And this we don't see.

Still, problems persist. One, in particular, is that "from Darwin onwards evolutionists have realized that if we arrange all our available fossils in chronological order they do not form a smooth sequence of scarcely perceptible change." But if macro- changes always reflect an accumulation of tiny fitness-increasing micro-changes, shouldn't the fossil record show a smoothly graded sequence of intermediaries between any two members of some lineage? The theory predicts this, yet trends in the fossil record are usually jerky, not smooth, and there is almost no fossil evidence for gradualism. We see big jumps, not finely graded sequences with little differences from fossil to fossil.

The favored explanation for this lack of correspondance between evolutionary theory and the actual fossil record is that the fossil record is grossly incomplete. As Darwin himself put it, in the evolutionary tree of life there must "be infinitely numerous transitional links" forming "the finest graduated steps" but "the geological record is extremely imperfect and this fact will to a large extent explain why we do not find interminable varieties, connecting together all the extinct and existing forms of life by the finest graduated steps."

But is this compelling? Does it satisfy our need to explain why we can find fossils for an organism at one point and then again millions or tens of millions of years later, without change? And is it convincing that whenever species alter the intermediate organisms always occur right where there are gaps in the fossil record? We return to these issues later.

 

Biochemical Mechanics

All the above was the theory of evolution before the discovery of DNA revealed exactly how the qualities of organisms could be encoded in minuscule genes and passed from generation to generation. Naturally, as the understanding of this macro-molecular process proceeded and biologists learned how genes dictate the shape and composition of an organism, and how DNA mutates and reproduces, another level was added to the theory of evolution.

DNA is a complex highly flexible chemical structure with a variable length backbone that offers an array of sites able to hold sequences of four different molecular proteins called nucleotides and denoted A, T, C, and G. It's like a scaffolding with four types of blocks hung on it. All human's have the same DNA addresses to hang blocks on, but potentially different blocks (from among the four) at each address. The patterns that the building blocks A, T, C, and G form as they slot into the addresses in each organism encode "instructions" for the development of that organism's features. More precisely, stretches of the DNA that include patterns that average about 900 nucleotides constitute genes. Depending upon the exact order of nucleotides in each particular gene (ATCCCGTTA....), when that gene becomes operative it stimulates synthesis of an enzyme which in turn facilitates chemical reactions that help regulate the growth of different cellular structures, or help transform chemicals into energy, or help fight off of microbes, or help bones grow, or help lungs breathe, or help muscles clench and limbs move, or help intestines digest, or help skin change its pigmentation, etc.

In any particular organism, every skin, bone, fin, and brain cell has the same DNA guiding its activity. The cells do different things, however, because right from the first embryological cell division, specific chemical features in the context surrounding each cellular instance of DNA determine what parts of that DNA become activated and what parts lie dormant. In some contexts we get liver cells, elsewhere brain cells, and in many places bone cells because different types of cells facilitate different enzymatic tasks due to existing in different places in the body offering different chemical environments which in turn cause different stretches of the cell's DNA to activate.

Infinitesimal strands of nucleotides encode recipes for the embryological emergence of whole organisms. No wonder Richard Dawkins tells his readers that "if they want to think about life," they "shouldn't think about vibrant, throbbing gels and oozes," but "about information technology." Realizing how complex the product of DNA-inspired chemical processes are, perhaps readers won't be too surprised to hear that there is enough storage capacity in the different patterns that A, T, C, and G can take in "the DNA of a single lily seed or a single salamander sperm to store the Encyclopedia Britannica 60 times over." In fact, modern genetic engineers could "write the New Testament or anything else into a bacterium's DNA" using patterns of nucleotides analogously to the way that one uses dots and dashes in Morse Code or 1s and 0s in binary computer code (though it would require about five centuries of person-labor to do it). Moreover, if this was done, the bacteria could then reproduce 10 million copies of the New Testament in a single day, though all 10 million "could dance upon the surface of a pin's head." And finally, if we could take care of the waste disposal problem and provide all the necessary nutrients, in just a few days we could have so many trillions of trillions of trillions of copies of these "religious bacteria" that they would occupy more space than the whole planet, and, shortly thereafter, more space than the whole known universe. No human-designed and created chemical factory has near the complexity of even a single bacteria. Far from making life appear mundane, a little knowledge can help reveal just how amazing it really is.

But, returning to evolution, in light of all the above we can see that a gene mutation is just a slight miscopying of DNA passed on from parents to offspring. This variation is random not because every conceivable mistranslation is equally likely, which is not true, but because each change that may occur has no in-built bias to either increase or decrease fitness in any particular direction. The traditional theory of evolution is that all direction therefore comes from selection.

And that's it. Ignoring details, that's where the theory of evolution according to natural selection stood until the recent innovations of, among others, Nils Eldredge and Stephen Jay Gould.

 

Punctuated Equilibria

Nils Eldrege reports that intellectually believing that "most evolutionary change would be slow, steady, gradual, and progressive," paleon<->tologists like himself and Gould expected that in exceptionally fossil<->iferous sequences they would "find sufficient examples to bear out this prediction." Remarkably, no paleontologists used the fact that they didn't find evidence of slow change in the fossil record to assert the theory's failure. As Eldredge put it, "the expectations of theory color perception to such a degree that new notions seldom arise from facts collected under the influence of old pictures of the world." In short, caught by the power of preferred descriptions, paleontologists automatically attributed the lack of fossil evidence for gradualism to gaps in the record, never considering that the gaps might be real and indicate instead that something other than gradualist evolution was at play. Contrary facts were ignored and only reassuring facts attracted study.

Elaborating on this intellectual phenomena as well as on his own theoretical journey, Eldredge reports in great detail his experience of digging in various locales to study the evolution of a particular trilobite, "Phacops rana." He sought to find steady gradual evolution to verify the Darwinian prediction yet over millions of years of evidence he found nearly no change until suddenly their emerged a layer of fossils showing the original species and also, simultaneously, a new species with a different visual system. In the gradualist view this apparent jump from one species to two had to be an artifact of poor fossilization: there must have been gradual change that wasn't caught in the fossil record. But Eldredge had the effrontery to ask about his Trilobites what now seems an obvious question: "why is all the gradual change [always] going on [only] in [the] gaps?"

Persistent digging revealed that the solution for the trilobite was that a geographic division separated off a small part of the original population of trilobites which underwent speciation elsewhere when the reproductively isolated small group of trilobites relatively quickly evolved new traits. Then, later, at the point where the new species re-joined the original population, the fossil record suddenly shows both species simultaneously. But Eldredge also noted--or perhaps a better word is "admitted"--that during most of the life of the Trilobite species there was no change at all. He saw that the evolutionary pattern was not steady graded change but a long period of stasis, then speciation via a relatively rapid burst of gradual change in a small isolated group undergoing natural selection, and then long stasis again.

Eldredge and Gould saw that this pattern of stasis, split off of a small number of organisms enjoying relatively rapid evolution, and stasis again, could neatly explain the supposed "gaps" in the fossil record as well as the longevity of unchanging strains. The brief bursts would be too short to be captured in a fossil record. All we would see would be new species occasionally popping up, no gradualism. Going against accepted wisdom, Eldredge and Gould advanced a new hypothesis for evolutionary change, which Gould called "punctuated equilibria."

As Eldredge puts it, "at the core of punctuated equilibria lies an empirical observation: once evolved, species tend to remain remarkably stable, recognizable entities for millions of years." Moreover, "new species arise very rapidly in small, peripherally isolated local populations." "The essential idea here is that new species--new reproductive communities--tend to bud off in some isolated region from a more widely spread ancestral species. Thus a second element is added to the simple notion of adaptive change through natural selection: the concept of the fragmentation of reproductive communities." And at the same time, a previously accepted tenet, gradualism, is challenged.

In short, instead of steady gradual changes, in the theory of punctuated equilibria "most evolutionary change occurs in a very short period compared to the lifetime of species" so that "new species...arise only when a small local population becomes isolated at the margin of the geographic range of its parent species," as what are called peripheral isolates. The "peripheral isolate develops into a new species if isolating mechanisms evolve that will prevent the reinitiation of gene flow if the new form re-encounters its ancestors at some future time."

The change Eldredge and Gould proposed was in part that "no one had ever claimed...that most (if not all) anatomical change in evolution, adaptive though it may be, happens not throughout the bulk of a species' history, but rather at those rare events when a new reproductively isolated species buds off from the parental species." But as we will see this was not the only innovation implied by punctuated equilibria.

The tenets of phyletic gradualism, which is the traditional Darwinian view, are: "New species arise by the transformation of an ancestral population into its modified descendants. The transformation is even and slow. The transformation involves large numbers, usually the entire ancestral population. The transformation occurs over all or a large part of the ancestral species' geographic range."

These tenets imply that "the fossil record for the origin of new species should consist of a long sequence of continuous, insensibly graded intermediate forms linking ancestor and descendant. Morphological breaks in a postulated phyletic sequence [can only be] due to imperfections in the geological record."

In contrast, the tenets of "allopatric speciation", which is the centerpiece of punctuated equilibria and means speciation by reproductive isolation of a small group, are: "New species arise by the splitting of lineages. New species develop rapidly. A small sub-population of the ancestral form gives rise to the new species. The new species originates in a very small part of the ancestral species geographic extent--in an isolated area at the periphery of the range." Discontinuous fossil records are an expected outcome, not a problem to be explained.

Punctuationism was greeted hostilely by many practicing biologists, paleontologists, etc. There followed a furor of highly instructive debate. But to understand its energy, we have to note one more implication of punctuated equilibria.

Dawkins points out that "an extreme anti-punctuationist taking the long-view of evolution, cannot see discrete species at all." There is only a "smeary continuum." But punctuated equilibria suggests that in fact speciation occurs in relatively short time spans so that species have births and deaths and really exist as specific entities in nature, not merely as useful abstractions that humans devise for cataloging purposes, as Darwin asserted, but as actual "individuals" capable of playing an evolutionary role.

This view of species as real things contradicted the popular understanding in the field when Eldredge and Gould offered their theory. For example, Gould reports that "J.B.S. Haldane, perhaps the most brilliant evolutionist of this century, wrote: `The concept of a species is a concession to our linguistic habits and neurological mechanisms'" while "a noted paleontological colleague" urged in 1949 that "a species...is a fiction, a mental construct without objective existence." And Eldredge reports that more recently a very influential text by T.H. Eaton, written in 1970 offered: "The connection of arbitrarily selected `species' in a time sequence, in fact their complete continuity with one another, is to be expected in all evolutionary lineages. But, fortunately, because of the imperfect preservation of fossil faunas and floras, we shall meet relatively few examples of this..."

For Eldredge, Eaton like all traditionalists back to Darwin, "shows the parallel between theories and party lines" since the theory "render[s] the picture of phyletic gradualism virtually unfalsifiable, [and] the picture prescribes an interpretation and the interpretation, viewed improperly as an `objective' rendering of data, buttresses the picture." Note also Eaton's use of the word "fortunately," indicating that he is actually celebrating a lack of knowledge, which should be pretty embarrassing behavior for a scientist.

To understand this, Eldredge and Gould argued that even beyond buttressing the traditional view, the reigning picture also "colors our language" causing us to use terms like `morphological breaks' which actually "presupposes phyletic gradualism," when in fact phyletic gradualism actually isn't really there in the first place. Similarly, the reigning picture "prescribes the cases that are worthy of study"--that is, the minuscule number of fossil lines where gradual intermediates can be found--since, "if breaks are artificial, the sequences in which they abound become, ipso facto, poor objects for evolutionary investigation." Eldredge points out, "surely there is something insidious here: if breaks are real and stand against the picture of phyletic gradualism, then the picture itself excludes an investigation of the very cases that could place it in jeopardy." And elsewhere, even more aggressively he says: "A theory of gradual, progressive, adaptive change so thoroughly rules our minds and imaginations that we have somehow, collectively, turned away from some of the most basic patterns permeating the history of life."

Eldredge and Gould not only pose their punctuated equilibria as a means of explaining evolution that is more consistent with the fossil record, they also seem to me at least to question that the traditional conceptualization can explain evolution at all. For Eldredge and Gould urge that once there is a reasonable accommodation between a species and its niche, if we accept the traditional view then no further evolution would ever occur. It does not suffice, they say, for the traditionalists to argue that inevitable changes in the environment would select new mutations. Eldredge and Gould reply that instead of sitting in a environment made newly hostile by a geological or climatic change while selection slowly works its wonders, species will track the old familiar environment in which they are comfortable as it moves around in space due to climate changes, or onsets of waterways, or mountains, or whatever. And, they say, "if a species cannot track its environment, its usual fate is extinction." This would leave Dawkins only the arms races and cooperative spirals as forces favoring ongoing evolution in the traditional theory. But, Eldredge and Gould seem to question this as well, or at least the arms race part of it, saying that evidence suggests that competition between species is rarely significant enough, if it ever even exists at all, to cause continuing trends of change.

So, on balance, Eldredge and Gould reject gradualism that is spread out over the life of each species, preferring spurts of stepwise but intense evolution prodded by speciation caused by the separation of small reproductive isolates encountering altered niches and unable to track their prior ones and in which changes can spread rapidly allowing accommodation before extinction. And Eldredge and Gould also believe, against the grain of their discipline, that species are real entities, with a major role in evolutionary dynamics. Indeed, Gould even says, "Evolution at higher levels is fundamentally a story of the differential success of species, not the slow transformation of lineages." Moreover, Eldredge and Gould may reject the traditional view not only as not revealing all that has happened, but as being logically incapable of explaining progressive evolution at all.

So what do the traditionalists now say about all this. Well, since the punctuationists have made considerable gains in the profession, the traditionalist defense is no longer complete rejection. Assimilation seems more the order of the day. Thus Dawkins says, "The fact is that, in the fullest and most serious sense, Eldredge and Gould are really just as gradualist as Darwin or any of his followers. It is just that they would compress all the gradual change into brief bursts, rather than having it go on all the time, and they emphasize that most of the gradual change goes on in geographic areas away from the areas where most fossils are dug up." Dawkins has a point in that punctuated equilibria is not necessarily totally hostile to Darwinist precepts and in the hand of Eldredge and Gould seems to preserve natural selection (Darwin's chief insight) as the directer of evolution. But urging, as Eldredge and Gould do, that all the mutation cum selection occurs in short bursts is nonetheless a significant change since it makes the birth and death of species each relatively quick events delineating species as real separate things. Dawkins skips over this to instead add that "It is the emphasis on stasis that is the punctuationists' real contribution, not their claimed opposition to gradualism, for they are truly as gradualist as anybody else." Okay, but regarding this Dawkins seems to have his doubts and he goes on to also say that to justify their belief in stasis the punctuationists "believe that there are genetic forces in large populations that actively resist evolutionary change," an idea which he ridicules by posing as counter evidence the ease with which we can selectively breed animals without encountering any built in resistance to change. Yet, the punctuationists' argument regarding the stasis of species that are not divided into a main group and a small reproductive isolate is premised on the species being able to move with their niches, on the one hand, and on having so many members as to swamp mutations before they can spread, on the other. Neither of these "forces resisting change" is addressed by the possibility of breeding in a lab or farmyard, since the lab and farmyard rule out exactly these factors.

Dawkins also denies the real existence or at least the real importance of species, saying that whether they exist or not, "they do little." Yet, the legitimation of macro evolution via "species selection" is what both Eldredge and Gould point to as the main innovation fostered by the theory of punctuated equilibria. The debaters don't seem to address the whole spectrum of each other's claims, presumably because, as Eldredge repeatedly notes, their ways of looking at the world tend to color what they see, even when "what they see" is each other's arguments--a phenomenon that transcends debates about evolution.

 

Species Selection

The usual rendition of evolution via natural selection claims that the only relevant unit of account are genes and the organisms that carry them. The bottom line is the spread of genes. Directional trends come from selection of individual palnts or animals for fitness.

But is this the only relevant scale in evolution? Could there be evolutionary trends premised on the life and death of whole species? This provocative question which may account for most of the fuss surrounding the punctuated equilibria perspective.

Thus we ask, is a species "an individual" in a sense that would allow selection for fitness among other species? As Dawkins tells us, "To a non-punctuationist the `species' is definable only because the awkward intermediates are dead." It is not an individual, not even a real thing at all since it has no boundaries in time. But as Dawkins admits, a punctuationist "sees each species as coming into existence at a particular time, and fading as well at a later time." The species has a beginning, end, and clear demarcation. There is no "smeary continuum." In a parallel argument Eldredge notes that species death by long-term gradual transformation to new species would be a problem for seeing each species as a type of individual since this type of transformation would blur the lines of definition. But Eldredge notes that since this happens very rarely, there is no problem. Instead extinction occurs due to not surviving in a hostile niche that can't be escaped so that it is a time bound event, like speciation in the first place.

So each species has the bounded geography it occupies as a physical limit, and an admittedly often very long but nonetheless precise span between its relatively rapid birth and extinction as its time limit. Moreover, a species even has a kind of glue holding it together and distinguishing it from the rest of its environment: reproductive affinity. Since these are exactly the earmarks of an "individual," Eldredge urges that punctuated equilibria "puts the icing on the cake in the argument that species are real historical entities, comparable in a formal manner to individual organisms." And, this being so, punctuated equilibria points to the possibility of "species selection" rather than only individual selection. In short, Eldredge can ask: are whole species more likely to persist or to go extinct in different contexts? And are they then selected for these different propensities so that what we see in natural history is partially a function of `species selection'?

Imagine a `species pool'--the whole planet with hundreds of millions of species, for example--whose content changes as species are born, go extinct, or bud new species. Suppose within a particular species small changes in the size of a representative organism offer no competitive advantage so that there is no pressure yielding gradual growth. Also suppose, however, that the species pool includes large and small species and, other things being relatively equal, that there is a greater probability that large species will be less likely to go extinct and more likely to bud off new species. In this case there could be a fossil trend toward growth due to "species selection" rather than individual selection. Indeed, within a species smaller could even be favored and yet the fossil record might still show growth in the size of organisms from new species to new species, occurring, of course, in punctuated "jumps." In fact, one might even suggest, along with Gould, that most of the trendlike change in evolution comes from this sort of species selection.

Consider the species level trait of being "uniform" in the sense of all the organisms in the species having only one means of survival--say eating one fruit--or, alternatively, "diverse" in the sense of all the organisms having many means of survival via a varied and flexible diet. Obviously the diverse "generalist species" is by definition able to thrive on many types of food, etc. and thereby better able to handle variegated habitats. Due to these traits it would tend to persist longer and spread over wider niches than uniform "specialist species." Interestingly, the generalist species might also tend to speciate less often because there would be fewer chances for a reproductive isolate to emerge, and, when one did, less likelihood that its environment would select for significant changes. On the other hand, we might expect specialized species to live relatively short species lives and also to speciate more, due to spawning more reproductive isolates and due to the increased probability that these isolates would not be so well adapted to their new environs as to not have their fitness enhanced by sequences of mutations.

If all this is correct, species selection operating on specialized species could yield a macro trend toward ever greater specialization as we move from species to succeeding species. And this would give us a strong case for the claim that trendlike evolutionary patterns could emerge from species selection as well as, or perhaps even instead of, individual selection within species. Though, we should add, one has to wonder whether this could yield the scale of changes evolution offers up.

There is a second interesting problem with all this, however. The logic implies, as Eldredge admits, that "one [shouldn't] expect generalists to show a pattern of rapid directional evolutionary change." But consider humans. On the one hand it would certainly seem that we are archetype generalists, having as we do the most varied means of survival and perhaps the broadest range of niche compatibility of any life form on the planet. Yet, the lineage we come from has also seen a remarkable trend of change--that is, a steady increase in brain size. This seems contradictory, but, in the manner of all scientists defending a theory, Eldredge has an interpretation that resolves the difficulty in a satisfying way. He says: "But perhaps human evolution is the exception that in the end proves the rule: for our sociocultural systems really are a highly complex evolutionary specialization. And these are rooted, in some arguable fashion, in our anatomical brains. We are, in short, more of a hybrid of generalist/specialist than most other creatures appear to be. And if this is true, perhaps we can better understand the curious mixture of pattern that our own evolutionary history seems to hold."

 

Broader Implications of Evolutionary Theory

Among the myriad of possible focuses for considering how evolutionary theory and evolution itself influence or could influence our understanding of other facets of life, the following constitute the issues I will explore in "Theories of Evolution II," in the next Salient Science article.

Is nature a realm of struggle and competition in which aggression and violence are rewarded above all else? Are social ethics contrary to a biology that emerges from a "struggle to survive"? Does biology in fact emerge from such a context?

If selection plays the predominant role in directing evolution, is it only selection among individual organisms, or is there also species selection which might be more prone to promote cooperation?

If selection doesn't play a critical role, if the punctuated equilibria analysis is moving in a useful direction in discovering faults in the Darwinian view, but hasn't moved far enough, what does explain evolution?

In any event, how much of "human being" comes from our genes: Shape, chemical function, physical capabilities, disposition to certain diseases, emotional inclinations, linguistic capacities, conceptual capabilities, behavioral dispositions, ethics? Are people and their behaviors mostly genetically or socially defined? What is a "biologically correct" environment for us?

Moreover, whatever human nature turns out to be, is there any sense in which humans are superior to all other organisms, and likewise in which all animals are superior to all plants? Or, alternatively, is it wrong to make such distinctions since each species exhibits an equally fine fit to its niche and moreover all species are merely sequential adaptations of the rest so that no higher and lower exists? What is a scientifically supported ecological/biological attitude regarding the chain of life?

Finally, at another level of analysis entirely, can prudent analogies to the way of thinking incorporated in theories of evolution help illuminate human history? For example, are there social institutions that arise from cooperative spirals of mutually enforcing social innovations? Is the pressure toward stasis in a species mirrored by analogous if differently constituted pressures toward stasis in society? Is there something historically comparable to the budding of reproductive isolates? Could new species correspond in some way to a new type society? Or, alternatively, if a non-selectionist dynamic explains evolution, does it have insights to lend to understanding human history?

Scientific sectarianism is perhaps not quite as common as political sectarianism, but it certainly exists and has dynamics quite similar to those pertaining in the political case, as Eldredge's description of paleontologists who ignored the real message of the fossil record revealed. But another attitude that we ought to bring to our own look at natural and human history also exists among scientists, and sometimes even political theorists. Darwin put it well: "I have steadily endeavored to keep my mind free, so as to give up any hypothesis, however much beloved (and I cannot resist forming one on every subject), as soon as facts are shown to be opposed to it." I will try to elevate this to a guiding principle in the "Theories of Evolution II" discussion.

The bulk of the quotations in this article are from two sources, each of which I heartily recommend: The Blind Watchmaker, by Richard Dawkins, Norton, 1986, for the mainstream Darwinist view, and Time Frames, by Nils Eldredge, Simon and Schuster, 1985, for the punctuationist view. Additional material was culled from the more philosophical, The Nature of Selection, by Elliot Sober, MIT Press, 1985, and the more entertaining but equally provocative The Panda's Thumb, by Stephen Jay Gould, Norton, 1980, as well as The New Biology, by Robert Augros and George Stanciu, New Science Library, which I will make use of again in Part Two of this article.