Genetics of Original Sin (4 page)

This method has been applied to a very large number of genes and continues to be applied more and more. Its results have confirmed—and sometimes corrected—a number of the conclusions derived from the study of fossils; especially, they have enormously enriched those conclusions. Indeed, the beauty of comparative sequencing is that it can throw light on the evolutionary history of any organism, not only those that have left fossil remnants. Fossils remain invaluable clues, of course, as illustrated by a number recently unearthed in China that have revealed several “missing links.” But the innumerable organisms, such as soft-bodied animals and, especially, bacteria and other unicellular organisms, that have disappeared without trace can be reconstituted by the magic of molecular sequencing.

The history of life is written in the genes of extant organisms. It is written in very fine print, which it has been our generation's
privilege to discover how to decipher. The general conclusion of all that has been learned is clear and indisputable: all known living organisms are descendants from a
single common ancestral form.

The notoriously cautious language of science is rarely so affirmative. But, in the present case, with all the debates that surround the so-called theory of evolution, it is necessary to speak out unambiguously. Evolution is not a theory, contrary to what is often stated, sometimes even by scientists.
Evolution is a fact.
It was a theory two centuries ago, when Lamarck and Erasmus Darwin first proposed it, just as heliocentrism was a theory in the days of Copernicus and Galileo. Evolution is no longer a theory, just as heliocentrism is no longer a theory; it is a fact. The Catholic Church has recognized this with remarkable promptness, as compared to the Galileo affair. On October 22, 1996, at a meeting of the Pontifical Academy of Sciences, Pope John Paul II solemnly announced that “
evolution is more than an hypothesis.
” He did admittedly retreat somewhat to make a special case for the creation of the human soul; and his successor has retreated even further by leaning in favor of the so-called theory of intelligent design (see
chapter 8
). Nevertheless, biological evolution is not negated by the Catholic Church. Such is not the case for several other religious groups.

Ever since Darwin, the notion of evolution has provoked opposition from religious groups. At one end of the spectrum are a number of fundamentalist Protestant Churches, especially in
the United States, that deny evolution because it conflicts with what is written in the Bible, held to be directly inspired by God and, therefore, literally true. In line with this belief and in spite of all the evidence to the contrary, they persist in affirming that the world was created by God in seven days, some five thousand years ago, as written in Genesis. They will not recognize that the Bible, at least the early parts of it, was written almost three thousand years ago by human beings, possibly inspired by God if that is the cherished belief, but using the knowledge and language of their time.

At the other end of the spectrum are the defenders of so-called intelligent design, who pretend to invoke no explicit religious motivation but merely claim that purely natural phenomena cannot account for all evolutionary events. There will be more about this “creationism in disguise” in
chapter 8
.

Between these two extremes, there is a form of creationism—sometimes referred to as “old Earth” creationism, as opposed to the “young Earth” variety based on a literal interpretation of the Bible—that similarly denies evolution and advocates instant creation of living species, but on a more flexible time scale, consistent with the fossil record. This form of creationism is more widespread and professed by members of other Christian churches, including some conservative Catholics, notably in Poland, and also by many Muslims and by a number of Orthodox Jewish scholars.
^*

Defenders of this form of creationism often accept so-called micro-evolution, which takes place within existing genera, but deny “macro-evolution,” the kind whereby new species arise from old ones. They use a number of allegedly scientific arguments to affirm, for example, that there is no valid proof of a descent of birds from reptiles or of reptiles from fish. As in
the days of Darwin, the origin of humankind from chimpanzee-like ancestors is the most contested aspect of modern evolutionism. This is where the official voice of the Catholic Church departs from the scientific account of evolution. The biological descent of humans is accepted; but creation of the human soul is seen as a special event.

Creationism is not just a religious creed. It claims to be a science, which deserves to be taught alongside evolutionary biology, or even in place of it. Its proponents have built powerful organizations in pursuit of this goal. They fight in court and try to convince legislatures to give equal weight to what they call “creation science” in school curricula, or even to abolish the teaching of evolutionary biology. They provide teachers, not only in the United States, but also in other countries such as Poland or Turkey, with costly, beautifully illustrated “textbooks” in which the facts of life are reinterpreted within a creationist framework. They also try to propagate their ideas among the general public by, for example, filling the bookshops around the Grand Canyon with pseudo-scientific pamphlets describing this beautiful illustration of the Earth's history as a recent product of the Flood.

Further discussion of this phenomenon, which is the object of numerous books and debates, does not belong in this book. Let it simply be said that it conveys the image of a Creator who deliberately filled the world with all sorts of false clues that lead scientists astray, including the geological strata, the fossils, the kindred DNA molecules with which phylogenetic trees are constructed, the radioactive isotopes that allow us to date the Earth's history, and all the other pieces of evidence that rigorous and honest investigators have collected and used in their efforts to understand nature. Such an image of the Deity as a willful mystifier is hardly one a sincere believer is likely to defend.

T
he beginnings of life on Earth are shrouded in the darkness of a very distant past, going back at least 3.55 billion years—more than three and a half million millennia!—according to microscopic traces believed to be of fossilized bacteria, detected in rocks of that age. It is interesting to place this event within the framework of the history of our planet and of the history of the universe.

The Big Bang, the primeval explosion taken by most cosmologists to have sparked our universe into being, took place 13.7 billion years ago according to the most recent estimate. The solar system was born some 4.55 billion years ago—when the universe was already more than 9 billion years old—from a swirling cloud of gas and dust that gradually condensed into the central Sun and surrounding planets, including the Earth. This birth was a violent affair, which subsided only about 4
billion years ago, when the Earth became covered with bodies of liquid water and became, for the first time, physically capable of harboring life. Less than half a billion years later, maybe much earlier but leaving no record so far discovered, life was there. It is not impossible that life appeared as soon as the Earth was physically ready to receive it, or almost.

How life started is the object of much research and even more speculation. Instant divine creation is one possibility, not only advocated by creationists but also implicitly accepted by a large number of laypeople, perhaps a majority, who see life as due to some kind of “vital spirit” that was initially “blown” into matter and still goes on “animating” it in every living being. Everyday language is permeated with this belief.

Unlike strict creationism, this view, known as “vitalism,” is not incompatible with evolution; it dominated biology for a long time, especially in France, where it was defended by many famous scientists, including Lamarck, one of the fathers of evolutionism, the celebrated Louis Pasteur, and, more recently, many other biologists, influenced by the philosopher Henri Bergson, winner of the 1927 Nobel Prize for literature, whose major opus,
L'Évolution créatrice,
recognized evolution, as the title says, but saw it as the product of an “élan vital,” a vital surge. Remarkably, the one-hundredth anniversary of the publication of this book was celebrated in France with some prominence in 2007, in spite of its outdated character. Today, vitalism is rejected by most scientists, with the exception of the advocates of intelligent design, who espouse the related
theory of finalism (see
chapter 8
). Thanks to the revolutionary advances of the last fifty years, we now understand and explain life entirely in natural terms.

The same can't be said of the origin of life, which is unknown so far. It thus remains permissible, while rejecting vitalism, to imagine, as some do, that life was flipped into being by a Creator, who subsequently left it to function and evolve under its own power, although such a conception of the deity does not fit with the more usual one of an omnipotent God who, notably, can be asked to change the course of things. As long as the origin of life can't be explained in natural terms, the hypothesis of an instant divine creation of life cannot objectively be ruled out. But this hypothesis is sterile, stifling any attempt to investigate the origin of life on Earth by scientific means. The only scientifically useful hypothesis is to assume that things, including the origin of life, can be naturally explained. If we start with the premise that they cannot, we may as well close our laboratories. Searching for an explanation that is taken, a priori, not to exist is futile (see also
chapter 8
).

So far, investigations based on this “naturalistic postulate” have failed to provide an answer to the problem of the origin of life but have achieved some progress. One of the most important findings of the last decades is that the small molecular building blocks of life, the sugars, amino acids, fatty acids, and nitrogenous bases from which are constructed the larger polysaccharides, lipids, proteins, and nucleic acids that make up the bulk of so-called living matter, arise spontaneously in various sites of our solar system and, probably, in many other
parts of our galaxy, as well as in other galaxies. These astounding facts, which belie the traditional view of
organic
chemistry as the prerogative of living
organisms,
were recently revealed by the spectral analysis of the radiation coming from outer space, by the probing of comets with instruments borne by spacecraft, and, especially, by the analysis, with all the resources of modern chemistry, of meteorites that have fallen on Earth.

Thus, what most likely constitutes the first stage in the origin of life is known. It is provided by cosmic chemistry, which, in innumerable parts of the universe, spontaneously generates the basic building blocks of life. Note that cosmic chemistry is not bioselective. It makes a gamut of organic compounds, of which some happen to participate in the building of living organisms, whereas many others do not. Subsequent events in the development of life have entailed a selection among the potential building blocks provided by cosmic chemistry.

From this naturalistic perspective, the products of cosmic chemistry are seen as landing in a milieu where some started interacting with each other to produce molecules of increasing size and complexity, which then interacted to produce polymolecular assemblages of increasing size and complexity, up to forming entities that could be defined as “protocells,” or primitive cells. Here is the snag. Nobody has so far succeeded in reproducing such a situation, or even a small part of it, in the laboratory.

One problem is that there is no agreement yet on what may have been the milieu in which it all started. Some believe
sunlight may have been needed as a source of energy. Others think that life originated in the darkness of deep waters. Debates also occur between proponents of a “hot cradle” and proponents of a “cold cradle.” According to the latter, the constituents of life are much too fragile to be able to survive long enough in a hot environment. The former, on the other hand, have been influenced by the fact that all the bacteria identified as most ancient by molecular phylogenies are thermophilic, that is, adapted to very hot environments.

Another point of disagreement concerns the relationship between the early chemistry that led to life and present-day biochemistry. Many specialists, impressed with the total reliance of biochemistry on the activity of protein catalysts, or enzymes, which obviously are too complex to have been present at the dawn of life, argue that there is no relationship between the two chemistries. Some, however, including myself (see
chapter 4
), see biochemistry as flowing congruently from that early chemistry.

As to the temperature that surrounded life's birth, I adopt the opinion, held by a number of experts in the field, that life probably started in hot volcanic waters, perhaps in one of those underwater formations, called deep-sea hydrothermal vents, or black smokers, that spew overheated, pressurized, sulfurous, metal-laden waters from fissures in the bottom of oceans and have been found, against all expectations, to harbor many strange forms of life.