Incredibly, as the second millennium drew to a close, the State of Kansas Board of Education voted to eliminate evolutionary theory from the state’s elementary school curriculum. Polls showed that only about a tenth of Americans could wholeheartedly accept the premises of Darwin- ism, that life has evolved to its present state through natural selection. “Creation scientists,” whose conclusions are biblically predetermined and whose arguments are based on the absence of some “missing links,” ignoring the tremendous body of positive evidence that does exist, are cited in the media as if they were real scientists. The Creation Science As- sociation for Mid-America helped write Kansas’ curriculum proposal, over the objections of biologists and educators, who now must attempt to teach religion disguised as science.
Science strives to remain skeptical and cannot refer to faith to judge the validity of theoretical constructs. The evidence for evolution of spe- cies through the mechanism of natural selection is widespread and pro- found; it is not an “unproven theory,” but is the very backbone of mod- ern biology. Religion is an important part of human life, but when religious beliefs based on faith are contradicted by empirical evidence that can be held in the hand and seen with the eyes, the evidence has to win. It is hard to see how anything can be gained by clinging to unsub- stantiated beliefs that contradict reality.
The disagreement between religious advocates and evolutionary sci- entists comes down to this: the creationists know how life began on earth, and the evolutionists don’t. The biologists are sure it didn’t arrive fully formed during one important week a few thousand years ago, but there is still plenty of debate in the scientific communities about the mechanisms that might have produced the first terrestrial organisms.
Wherever they came from, the first molecules of life appeared on this planet when it was very young. The earth formed about four and a half billion years ago, and the earliest known signs of life date back to 3.45 billion years ago—just 300 million years after the surface of the earth had cooled enough to allow the survival of living things. Those first living molecules were most likely suspended in water with other chemicals. As the earth’s atmosphere, in what has been called for obvious reasons the Hadean Eon, was very different from what it became after the evolution of oxygen-emitting flora, we can expect that the surface of the planet was constantly scorched with solar radiation that tore at fragile molecular strands. Volcanoes belched poisonous sulphurous gases into the
atmosphere. Uranium 235 was 50 times more abundant than it is now and bombarded the environment with deadly radioactivity. Corrosive compounds would have torn at those primal organisms; lightning and lava and other volatile forces must have made the environment very hard to endure. Somehow in that tough world the self-replicating mole- cules continued to increase in number, surviving, mutating, changing, adapting to conditions in the liquid, and on the solid land, and in the at- mosphere, such as it was then.
What did it take to survive in that environment? Some microor- ganisms mutated in ways that doomed them, that caused them to fail to reproduce, and some formerly secure molecules (the first living things must not have been much more than that) found themselves in envi- ronments that destroyed them. On the other hand, some mutations improved the molecules’ chances of reproducing, and occasionally mu- tations improved their ability to adjust to conditions that were previ- ously forbidding, so the simple life-forms could extend their territory to new kinds of surroundings. The environment presented a kind of chal- lenge, to which the evolving molecules needed to be able to respond; if the environment was a problem, then emerging life needed to evolve a solution to it. Where dangers prevailed, either reproduction ceased or mutation resulted in adaptive features.
The early environment was of course very different from what we have today. We could even say that life todayisits own environment, or at least has evolved its own world. The adaptations of the first life-forms would not be adaptive today. Evolution is a constantly adjusting process, with organisms changing to meet the requirements of an environment that contains themselves and other organisms. One of the products of that process is the thinking ape,Homo sapiens.
Gaia: The Living Earth
Widening the zoom, it is possible to view the entire planet earth as one large organism, with various plant and animal species carrying out their functions much as cells do in our bodies. The atmosphere, the oceans, dry land, and the species that inhabit them conspire (literally, “to breathe together”) to maintain the health of the biosphere. It is also pos- sible to view a species as a single distributed organism whose component parts are the individuals who carry on and perpetuate the genetic heri- tage, and it is possible to see individual organisms as vehicles for even smaller viable units, and so on ad infinitum. There is no “correct” zoom
angle for looking at nature, but it is interesting, perhaps even enlighten- ing, to try looking through different-sized scopes.
In the late 18th century James Hutton, who is now known as the fa- ther of geology, wrote that he considered the earth to be a superorganism whose characteristics should be studied by a kind of science resembling physiology. His argument, which he called uniformitarianism, was that the physical earth had undergone many changes as a result of life’s pres- ence. Two hundred years later, British chemist James Lovelock (1979, 1988) revived the idea that the earth is a living organism, calling his view
the Gaia hypothesis. Lovelock (1972) wrote his famous controversial
statement in the journal Atmospheric Environment: “Life, or the bio- sphere, regulates or maintains the climate and the atmospheric composi- tion at an optimum for itself.”
As evidence for the Gaia hypothesis, Lovelock noted that the atmo- spheres of Mars and Venus are stable with 95 percent carbon dioxide, though there is only a trace of it in the earth’s atmosphere. His argument was that early life-forms, especially algae and bacteria, took the carbon dioxide out of the air and replaced it with oxygen. Oxygen is not usually found plentifully (it makes up more than one-fifth of the earth’s atmo- sphere), as it is a very volatile element; it easily combines with other chemicals in the phenomenon we call combustion, or fire. The earth’s at- mosphere is stable, though the combination of gases that comprise it is extremely unstable. The earth exists in a state of deep chemical disequi- librium, balanced, as it were, at the edge of chaos.
While Lovelock’s hypothesis was eagerly accepted by whole-earth en- vironmentalists and New Age philosophers, more hard-nosed natural scientists were reluctant to accept it. The main point of contention had to do with the implication that the earth-organism had a sense of pur- pose, as suggested by the idea that the planet is “trying” somehow to maintain an environmental state that is beneficial for itself. In conse- quent discussions, Lovelock admitted he had confused the situation by introducingteleologicallanguage, that is, language that implied purpose. He revised his statement to reduce this effect, removing implication of the “will” of the superorganism from the hypothesis. Whether the de- tails of the theory are ultimately confirmed or rejected, it is relevant for our discussion simply to consider human life and thought from this level, as a force or factor in dynamics on a global scale.
Also relevant for our discussion, Lovelock demonstrates Gaia theory dynamics in a computer simulation he calls Daisyworld. In one version, Daisyworld is a virtual planet upon which three species of daisies, a dark species, a gray species, and a light species, grow. In the beginning, the planet is cold, as its young sun has not yet reached full strength; the dark
daisies are better suited to that kind of climate, as they are able to hold the heat from the world’s sunlike star. They would reproduce, taking over the world, but their heat absorption ends up heating the surface of the Daisyworld, until it becomes inhospitable for the dark daisies, too warm for them (A in Figure 3.1), and their numbers decrease quickly. By warm- ing the environment, however, the dark daisies have made it a good place for white and gray daisies to thrive; these lighter daisies cool their environment by reflecting heat (B). As the young sun reaches its full strength, the lighter daisies have even more advantage, and as their numbers grow, their effect is to bring the planet’s temperature down (C). The prevalence of the white daisies keeps the planet’s climate much milder than it would have been without life (D). Thus with no knowl- edge of the environment, and with no intent to do so, the biosphere is able to make adjustments that keep it relatively optimal. The Daisy-
Dark Light Time A C D Daisyworld Gray Dai sy popul at ion S u rfa ce tem p er at ur e B Temperature without daisies Temperature with daisies
Figure 3.1 Lovelock’s Daisyworld simulations let several species of daisies—in this case, Dark, Gray, and Light—grow in their optimal climate. (Adapted from Lovelock, 1988.)
temperature, number of species, heat of the planet’s sun, and so on, with a consistent result: through selecting the prevalence of each variety of daisy, the system maintains the temperature at the planet’s surface at a viable level.
Gaia theory holds that the entire planet functions as one single inte- grated organism, including “inorganic” systems such as the climate and the oceans as well as the biosphere. It is a literally global view that places individual organisms and even species in the roles of cells and subsys- tems, supporting the larger dynamical system through their breathing, eating, breeding, dying. In yet another blow to the human ego, this per- spective seems to trivialize the individual—in fact, from the Gaia per- spective our species appears to be more of a blight or a cancer than a beneficent organ of the planetary body. Our contribution seems to be to introduce disturbance, imbalance, disruption. So far, seen from the plan- etary perspective, our human intelligence has simply empowered the de- struction of a global system that preceded us by billions of years.
Differential Selection
In 1962, the Scottish ecologist V. C. Wynne-Edwards theorized that evo- lution selected against animals that reproduced too much, to prevent overpopulation and decimation of a species. He stated:
Experiment generally shows that . . . many if not all the higher ani- mals can limit their population-densities by intrinsic means. Most important of all, we shall find that self-limiting homeostatic methods of density-regulation are in practically universal operation not only in experiments, but under “wild” conditions also (Wynne-Edwards, 1962, p. 11).
According to him, many behaviors that had previously been unex- plained, for instance, noisy group vocalizations, communal displays, and winter roosting aggregations, might serve the function of informing species members about the size of their population. With this knowl- edge, species could adjust their reproduction rate to maintain equilib- rium, avoiding the disaster they could cause by overextending them- selves in their limited environment. Acknowledging that many species live in social groups, it may be that a trait resulting in reproductive re- straint would survive if it provides advantage for the group as a whole.
The problem with Wynne-Edwards’ model, called group selection, is that the theory must assume the existence of a gene that carries an auto- matic selection against itself. If a gene resulted in a reduction of repro- duction (e.g., through delayed fertility or some instinctive form of infan- ticide), then its frequency would decrease as competing genes—ones that reproduced at a higher rate—dominated the population. The idea has been controversial since it was first proposed; if members of a population risk fatal sacrifice, then their genes would be less likely to be passed on to succeeding generations. Though the concept is not subscribed to by most biologists today, argument regarding group selection did focus in- teresting discussions on the question of altruism, which is seen widely through nature and presents some fascinating puzzles to evolutionary theorists.
In 1964, W. D. Hamilton proposed an explanation for behaviors that don’t make sense under the assumption that individuals seek self-gain.
Inclusive fitnessis the concept that organisms strive to ensure the survival
of others whose genes most resemble their own. He observed that altruis- tic behaviors frequently increase the probability of the altruistic individ- ual’s genes being passed on, even when the individual will not be the ac- tual ancestor. Animals will sometimes risk or sacrifice their own lives to guarantee the survival of their genetic relatives—noting the confound- ing fact that a local group of conspeciates is likely to contain numerous near kin. A mother animal who charges a predator to save her offspring risks paying the ultimate cost to herself individually, yet it happens every day, in very many species. The same goes for animals who give a warning call in the presence of a predator, thereby calling attention to them- selves. Inclusive fitness suggests that there is a general tendency in na- ture for genes to do what they can to improve their own chances, even at the cost of individual lives. The majority of self-sacrificing altruistic be- haviors seen in nature are performed in the service of siblings, offspring, and cousins.
Think of the cost of reproduction itself. To reproduce means having to have sexual intercourse, which puts an animal in a vulnerable situa- tion, besides forcing it to associate with its potentially dangerous—some- times cannibalistic—conspeciates. Being pregnant, as we know, means eating for the number in the litter plus one, besides slowing the mother down and making her easier prey or a less adept predator. The cost of nurturing a litter is extremely high; the mother, and sometimes the fa- ther, must keep the helpless little ones safe and well fed, and parental sacrifices are high. If the system were oriented around the individual’s needs, would we choose to take on all these troubles? Animals’ lives,
including our own, are organized around the phenomenon of reproduc- tion, from courtship to sexual jealousy to altruistic protection of kin.
Darwin was puzzled by marked differences between the sexes in many species. For example, male elephant seals weigh four times as much as females (4,000 pounds to 1,000)—how could this have hap- pened, if both sexes faced the same challenges from the environment? Males of some species have developed heavy antlers or plumage that ob- viously imperils their ability to escape predators. In response to these paradoxes, Darwin created a kind of second theory of evolution, having to do with the evolution of sexual characteristics. Though it was not widely accepted at first, the theory ofsexual selectionis now considered to be an important part of evolutionary theory. If we consider that evolu- tion works via a process of differential reproduction, it seems obvious that features that promote reproduction per se—and not necessarily ad- aptation to environmental challenges—will be selected along with adap- tive features.
Further, it is apparent that the investment in reproduction is different for males and females, especially in species such as humans where the pregnancy is relatively long and the newborn offspring are helpless. Ac- cording to sociobiological theory, “sexier” individuals have more oppor- tunities to mate, for almost all species (though standards of sexiness ad- mittedly differ from species to species!). Where females have an innate preference for mates who can provide shelter and protection, males have an interest in choosing mates who show signs of being fertile. Further, because maternity is certain but paternity is not, it is in the male’s best interest to elicit a long-term, exclusive sexual commitment from the fe- male; otherwise he may invest much in perpetuating somebody else’s genes. On the other hand, as the male is capable of impregnating multi- ple females, there is less pressure for males to be sexually exclusive, and in fact evidence is accumulating that human males tend to be more pro- miscuous than females across cultures.
This is illustrated by a phenomenon known as the Coolidge Effect, named after former U.S. President Calvin Coolidge. The story goes that President Coolidge and his wife were touring a farm. When the First Lady came through the chicken house, the farmer mentioned that roosters are capable of copulating many times in a single day. “Please mention that to the President,” she requested. When the President came to the chicken house, the dutiful farmer repeated the fact to him. Silent Cal contemplated this for a few seconds, then asked, “Same hen every time?” “Why, no,” said the farmer. “Please mention that to Mrs. Coolidge,” said the President.
Hölldobler and Wilson (1990) argued that a colony of ants should be thought of as a single superorganism. In order to understand ant behav- ior it is necessary to look at the behavior of the colony as a whole, rather than the individual. In fact some species of ants die at a rate of 6 percent of the population per day; thus it would seem that the individual’s con- tribution cannot be very great.
The slavish subjugation of the individual to the needs of colonies of social insects of the orderHymenoptera, which includes ants, termites, bees, and wasps, can be explained uniquely in terms of kin selection. Hamilton noted that species in this order reproduce by a method known
ashaplodiploidy(see Figure 3.2). Females inherit half their alleles from the
mother. Assuming a 50 percent chance of receiving either of two copies