Genetics of Original Sin (14 page)

This view is not new. It was known in the past as finalism, or teleology, a doctrine close to vitalism that sees life as a goal-directed process (which implies someone or something that does the directing). This is, indeed, the appearance life gives to the observer and is reflected in the common language: we say that the lungs are
for
breathing, the stomach and intestine
for
digestion, and so on. Replacing such statements by “the lungs, or the stomach, happen to be such that they can function in breathing, or in digestion” is counterintuitive but more consonant with current thought, which sees these organs as emerging by natural selection because they were accomplishing functions useful to survival and multiplication of the organisms in which they first appeared. The term “teleonomy” is often used, in opposition to “teleology,” to qualify the
apparent
purposefulness of biological structures.

Defenders of intelligent design use several arguments. One, by the American biochemist Michael Behe, is “irreducible complexity,” the property of systems made of several parts, each of which needs specific features to fit within the whole. He gives the “simple mousetrap” as a model of irreducible complexity and goes on to cite complex biochemical systems, such as blood coagulation or motor organelles like cilia and flagella, as examples of assemblages that could not have come together without the assistance of some entity that conceived the machinery, foresaw its use, and designed the various parts accordingly. Two centuries earlier, the English theologian William Paley made a similar argument in his famous watchmaker analogy, which served as basis for his
Natural Theology; or, Evidences of the Existence and Attributes of the
Deity Collected from the Appearances of Nature,
which was first published in 1802: you find a watch and deduce that there must have been a watchmaker.

The New Zealander Michael Denton cites as evidence of intelligent design certain evolutionary transitions, such as the passage from reptile to bird. He points out that so many changes had to take place concurrently, in skin, bones, lungs, and other organs, that they could have happened only under the instructions of a designer who knew what the final product would look like.

William Dembski, an American mathematician, evokes the familiar sequence paradox. The calculation is simple. Take twenty different kinds of letters (representing the twenty kinds of amino acids with which proteins are constructed) and use them in all possible combinations to make words. The number of different possible words, known as the “sequence space,” increases with the length of the words. It is four hundred for two-letter words, eight thousand for three-letter words, in general, 20
ⁿ
for words of
n
letters. Many protein “words” have lengths of three hundred or more amino acid “letters,” which corresponds to a minimum of 20
³⁰⁰
, or 10
³⁹⁰
different words. There is simply no way such a number could be represented, except by filling an entire paragraph with the figure 1 followed by 390 zeros, which is essentially meaningless. It dwarfs the biggest natural numbers we can think of, such as the number of stars in the universe (10
²²
) or even the number of elementary particles in the universe (10
⁴²
). Even the number of different fifty-letter words (20
⁵⁰
, or 10
⁶⁵
) already exceeds this range. For Dembski—and for a number of theoreticians who have made the same calculation before him—the conclusion is clear: proteins could not, without guidance, have reached the “infinitesimally minuscule” spot they occupy in their “immeasurably immense” sequence space.

At first sight, such reasonings may be appealing and even seem compelling. Take a case such as mimicry (
chapter 7
). To an observer faced with an insect that can hardly be distinguished from the leaf on which it sits, the simplest explanation that comes to mind is that of an agency that modeled the insect as a copy of the leaf. The natural explanation, which posits a very large number of small steps in which the ancestral insect each time became a little more leaflike, enough so to gain a selective edge over the others, is, in a way, much harder to swallow, especially if one adheres to the notion of a creator. A God who created life and endowed it with its properties should know enough about genetics and its applications to be able to carry out the changes that make a beetle look like a leaf and help it avoid predators.

It is thus no wonder that intelligent design has been so warmly received among various religious circles, including those that reject biblical creationism. The Catholic Church, for example, has recently been leaning in this direction, first in the words of the Austrian cardinal Schönborn, later endorsed by the pope himself. This is understandable and even logically consistent. For one who believes in a God capable of granting prayers and even performing miracles, directly or through persons of exceptional saintliness, it is not difficult to imagine this God occasionally giving evolution a nudge in a direction of his choice, especially if, as is firmly asserted by Catholic doctrine and several other theistic religions, one believes this choice to include the advent of humankind. But that is not the question. It is, even for the believer, to know whether the nudge was necessary or whether events could have happened naturally. We shall see that the advances of sciences do not favor intelligent design.

In the United States, the issue has become political, even legalistic. The question is not so much whether intelligent design
is right or wrong, but whether its teaching in schools as an alternative to natural selection contravenes the separation between church and state. From the didactic point of view, this way of handling the situation ignores the fact that intelligent design is advocated by a significant number of people and the object of much public debate. My preference is to allow discussion of intelligent design and thereby demonstrate why it fails and why Darwinian natural selection succeeds in showing how evolution works. But such discussions would perhaps put an unfair burden on teachers and would probably be even more controversial than banning the subject outright from the curriculum.

Refuting intelligent design is easy and does not require any specialized knowledge. Intelligent design is simply
not a scientific theory.
Science is based on the working hypothesis that things are naturally explainable. This may or may not be true. But the only way to find out is to make every possible effort to explain things naturally. Only if one fails—assuming failure can ever be definitely established—would one be entitled to state that what one is studying is not naturally explainable. The entire history of science, including the dramatic advances of biology in the last fifty years, is there to validate and consolidate the naturalistic postulate. Now is hardly the right time to abandon this cornerstone of the scientific endeavor. Yet, this is exactly what intelligent design does, by stating a priori that certain evolutionary events are not naturally explainable, thus ruling out the possibility of ever finding the explanation if there is one (see also
chapter 2
). Just tell this to the students and let them draw their own conclusions. It has nothing to do with religion.

At the scientific level itself, the arguments put forward in support of intelligent design can easily be dissected, as many
critics have done, and shown to rest on oversimplified views of the evolutionary process, which ignore the immense times taken, the circuitous pathways followed, and the large numbers of individuals and generations involved. Complex biochemical systems, for example, have arisen from simpler ones by way of many steps that are only now beginning to be identified. Similarly, evolutionary pathways that have often been viewed as almost miraculous are now being elucidated. The history of the eye, for example, which has evoked so much wonder and puzzlement, has been largely reconstructed, starting from a small light-sensitive spot in some primitive organism and branching out into at least six different directions.

As to the sequence paradox, we have seen in
chapter 4
that the structures of present-day proteins and other observations indicate that these molecules started as short chains. It is conceivable that the molecules were short enough for all possible sequences, or almost, to be realized (by way of their genes) and submitted to natural selection. Combination of the sequences retained by this first screening could have yielded an essentially complete set of the longer sequences achievable with the starting sequences, leading once again to pruning by natural selection, and so forth, up to the sequences of hundreds of amino acids that prevail today. In other words, proteins would not have reached in one shot the “infinitesimally minuscule” spot they occupy in their “immeasurably immense” sequence space, as assumed by Dembski, but by a stepwise pathway subject at each stage to natural selection.

Much remains to be discovered, but so much has already been found that one can only be urged to look for more, rather than give up and invoke supernatural influences of unknown nature.

W
e enter the last episode of the history of life, the one that concerns us most directly, as we are its outcome (most likely provisional, as evolution is far from finished). In this part of the book, I briefly retrace the main steps of hominization, paying special attention to the development of the brain, which is its most outstanding event, and to the latest developments that have led to today's world, totally dominated—and threatened—by the inordinate success of the human species.

I conduct this analysis in the light of the notions that are available on the earlier history of life and on its mechanisms, with as main source of illumination the “beacon” of natural selection. I thus arrive at the book's central theme: “original sin” reinterpreted in the light of knowledge, namely the genetic flaw imprinted into human nature by natural selection.

L
et us go back about three and a half million years. On the human scale, this is an immense time span: thirty-five hundred millennia, five hundred times the duration of the whole of recorded human history. But, in the framework of the history of life (more than three and a half million millennia), or even of animal life (six hundred thousand millennia), it is little more than a brief coda.

The site of our flashback is in Africa, in the arid Laetoli region in northern Tanzania. The focus of our attention is a small band of strange creatures of mixed ape-human appearance, revealing their ape kinship by their short size (about four feet), dark, hairy skin, flattened forehead, projecting jaws, and small cranial volume, but walking upright on two legs and holding things in their hands, like humans. We know of them through an amazing set of footprints almost miraculously preserved in solidified volcanic ash, discovered in the late 1970s by the renowned South African couple Louis and Mary Leakey. We have some idea of what these creatures looked like from the world-famous Lucy, the nearly complete skeleton of a young female unearthed in 1974, in the Afar region of Ethiopia, two thousand miles to the north of Laetoli, by a team including the Frenchman Yves Coppens and headed by the American Donald Johanson, who named it after a Beatles song that was incessantly played in their camp, “Lucy in the Sky with Diamonds.” Lucy and her congeners are known under the misleading name of
Australopithecus
(literally “southern ape”), which was invented in 1925 by the Australian anthropologist Raymond Dart, who chose it, not because of his nationality, but because South Africa is where he discovered the so-called Taung child, which is the very first prehuman fossil found in Africa, the first clue pointing to this continent as the cradle of humanity.

Where did
Australopithecus
—or rather, australopithecines, as there were several kinds—come from? To answer this question, we must move back several more million years, to the time when the African continent had just been split from north to south by a deep tectonic fracture that gave rise to the Great Rift Valley. This upheaval dramatically altered the local landscape and climate, especially east of the cleft, where the forest gave way to savannahs and to vast, barren areas, episodically exposed to rainfalls that transiently filled the dry riverbeds with rushing streams. This change in the landscape played a decisive role in the advent of humankind, according to a theory, popularized under the name of “East Side Story,” proposed by the French anthropologist Yves Coppens (encountered above as a member of the team that discovered Lucy) and endorsed by a number of investigators.

According to this theory, about seven million years ago, a small band of apes, originally belonging to a forest-dwelling group ancestral to present-day chimpanzees, found themselves
cut off from the bulk of the group and trapped east of the Rift, where they were exposed to challenging new environmental conditions. They responded to these challenges—so the story goes—by the acquisition of bipedalism, a mode of locomotion that helped them walk economically through the savannah, raise their eyes above the tall grass to spot dangerous predators, and use their hands to carry objects and fashion tools. Bigger brains, better able to coordinate physical activities and to design survival strategies, also evolved over time and helped these early hominids to prevail in their new environment.

This attractive theory has recently received a serious blow from another Frenchman, Michel Brunet, who has discovered what look like prehominid remains—mostly cranium pieces showing some human features—dating back as much as six to seven million years, in the Djurab desert of the Chad region, far to the west of the Great Rift Valley. Called
Sahelanthropus tchadensis
by its discoverer, to stress its human character, and nicknamed “Toumaï,” a name meaning “life hope” given locally to children, the new fossil has obviously undermined the “East Side Story” scenario. But its significance should not be overestimated.