Why Darwin Matters (22 page)

In the 1960s, Secretary of Defense Robert McNamara besieged the American public with eye-blurring statistical charts and graphs to demonstrate that we were winning a war in Vietnam that we were actually losing. Four decades later, Secretary of Defense Donald
Rumsfeld attempted the same sleight of hand, when he employed his infamous epistemology of known knowns, known unknowns, and unknown unknowns to explain the apparent nonexistence of Iraqi weapons of mass destruction.
³

Creationists, Intelligent Design theorists, and outsiders to science often mistake the latter two categories for signs that the theory of evolution is in trouble, or that contentious debate between what we know and do not know means that the theory is false. Evolution is rich in controversy and disputation over the known and unknown. In reviewing what is on the cutting edge of debate within evolutionary biology, we discover the real questions we should be asking about evolution. If Intelligent Design creationists want to “teach the controversy,” here are just a few of the major questions scientists are asking—and hoping to answer—about the origin and evolution of life.

Creationists revel in “how did it all begin?” questions, and the opening session of the Evolution Summit was on the origins of life, starting with a lecture by Antonio Lazcano, President of the International Society for the Study of the Origin of Life and a scientist at the Universidad Autónoma de México. Lazcano theorized that there were three sources for the primordial soup: volcanic out-gassing, high-temperature submarine vents and fumaroles, and outer space—the 4.6-billion-year-old Murchison meteorite, discovered in Australia in 1969, for example, was loaded with such chemical building blocks of life as amino acids, aliphatic and aromatic
hydrocarbons, hydroxy acids, purines, and pyrimidines. “The evidence strongly suggests that prior to the origin of life the primitive Earth already had many different catalytic agents, polymers with sequences of nucleotides, and membrane-forming compounds,” Lazcano inferred, concluding that this prebiotic soup led to the first replicators, most likely RNA, and this led to the more complicated DNA replicator of today.

In his commentary on Lazcano’s lecture, the UCLA paleobiologist William Schopf,
pace
Rumsfeld, asked: “What do we know? What are the unsolved problems? What have we failed to consider?” Schopf answered himself: “We know the overall sequence of life’s origin, from CHONSP [carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus], to monomers, to polymers, to cells; we know that the origin of life was early, microbial, and unicellular; and we know that an RNA world preceded today’s DNA-protein world. We do not know the precise environments of the early earth in which these events occurred; we do not know the exact chemistry of some of the important chemical reactions that led to life; and we do not have any knowledge of life in a pre-RNA world.” As for what we have failed to consider, Schopf suggested that the “‘pull of the present’ makes it extremely difficult for us to model the early earth’s atmosphere and the biochemistry of early life.”

Later, Lynn Margulis, in her inimitable rapid-fire style, hit Lazcano with a point-blank question: “In your opinion, what came first, cells or the RNA world?” Lazcano answered: “If you define a cell as a membrane-enclosed system, then lipids-enclosed systems assisted in the polymerization of molecules, which led to RNA.” Cells first, replicators second.

One of the creationists’ favorite tactics is to focus on gaps in the fossil record, and there is no bigger gap, they claim, than the so-called “Cambrian explosion,” a geologic period starting around 540 million years ago during which many of life’s major taxa first made their appearance in the fossil record. Intelligent Design theorist Stephen Meyer portrays this “explosion” as a single and instantaneous event, rather than the reality of its development over a fifteen- to twenty-million-year period. (Paleontologists usually modify their description of the Cambrian “explosion” by noting that this is a “geological” moment that, by comparison to biological or human time, is glacially slow.) In fact, Meyer’s paper challenging the standard evolutionary model of the Cambrian explosion was the first creationist paper ever published in a peer-reviewed scientific journal, and creationists have made much of that fact.
⁴

Too bad Meyer was not present when Mikhail Fedonkin, head of the Laboratory of Precambrian Organisms at the Paleontological Institute in Moscow, reviewed the evidence for evolution in the billions of years preceding the Cambrian period. Fedonkin suggests that a fall of global temperatures, and the oxygenation of the biosphere caused by photosynthesis, played major roles in the dramatic change in the availability of heavy metals that he believes were crucial in the metabolic processes that led to the evolution of complex life. This metal-rich environment served as a catalyst: “Over 70 percent of known enzymes contain metal ions as a cofactor of an active site. Fast catalyzed reactions segregated life first dynamically and then structurally from the mineral realm.” Once simple prokaryote cells gave rise to complex eukaryote cells, life
was off and running, resulting quite naturally in the Cambrian eruption of complex hard-bodied organisms.

Commenting on Fedonkin’s findings, Stefan Bengtson from the Swedish Museum of Natural History asked, “Why did the build-up to the Cambrian ‘explosion’ take so long?” Noting that 99.99999 percent of all species that ever lived have gone extinct, Bengtson answered his own question: “We do not know because we have nothing else to go on. Life is an evolutionary bush, not an evolutionary tree, but our data based on extant life induce us to prune the bush into a tree, so we need more data.”

Richard Fortey from the British Museum of Natural History investigates the importance of mass extinction events in resetting the direction of evolution, the magnitude of evolutionary arms races in driving morphological innovation, the relationship of climate change to evolutionary change, and the extent to which evolution can be described as directional. With half a billion years of a rich fossil record, Fortey said, we can track evolutionary periods of creativity and crises. Stephen Jay Gould’s 1989 book
Wonderful Life
stimulated a lot of new ideas about the Cambrian explosion of life’s diversity, he continued, and it soon became clear that there were an extensive variety of organisms difficult to classify, such as those found in the Cambrian-era Burgess Shale. But there are a number of Cambrian fossil beds, such as in China, where important phyla such as Chordata evolved. “In the Cambrian, some claim that there were as many as a hundred phyla, but the evidence does not support this. We now believe that morphological diversity did not explode as much as Gould originally suggested, although the explosion in
evolutionary experimentation was real. By the time we get to the Cambrian, as at the Burgess Shale, the systems are very complex, such as trilobite eyes. Evolution was experimenting with many wondrous varieties, such as all the armor on the heads of trilobites.”

Intelligent Design theorists argue that evolutionary theory cannot account for the increase in organismal complexity. That is, how can we explain the increase of information in something like the genome in a world filled with entropy and the decay of information? This problem is addressed by Peter Gogarten, a professor of molecular and cell biology at the University of Connecticut, who demonstrates how often prokaryote organisms (simple cells like bacteria) experience horizontal gene transfer between organisms. They swap genes! “Over long periods of time gene transfer makes organisms existing in the same environment more similar to one another. This is most clearly seen in the case of organisms that live in environments that are otherwise inhabited by distant relatives only.” Thus, Gogarten concluded, “the boundaries between prokaryotic species are fuzzy. Therefore the principles of population genetics need to be broadened so that they can be applied to higher taxonomic categories.”

If organisms can swap genes, they can also acquire genes and thereby increase the information complexity of their genomes. If Lynn Margulis is right, this is in fact how simple prokaryote cells evolved into complex eukaryote cells (of which we are made), through symbiogenesis, which she described succinctly as “the inheritance of acquired genomes” and more formally in its relationship to symbiosis as “the long-term physical association between members of different types (species).” The problem with making
evolution primarily about genetics (neo-Darwinism), Margulis concluded, is that “[r]andom changes in DNA alone do not lead to speciation. Symbiogenesis—the appearance of new behaviors, tissues, organs, organ systems, physiologies, or species as a result of symbiont interaction—is the major source of evolutionary novelty in eukaryotes: animals, plants, and fungi.”

Creationists and Intelligent Design theorists also like to claim that the theory of evolution is a faith-based religion to which scientists must swear allegiance in order to obtain research grant money. They should have heard Margulis bellowing from the dais that neo-Darwinism is dead. Echoing Darwin, she said, “It was like confessing a murder when I discovered I was not a neo-Darwinist.” But, she quickly added, “I am definitely a Darwinist. I think we are missing important information about the origins of variation. I differ from the neo-Darwinian bullies on this point.” Neo-Darwinists tend to focus on plants and animals, Margulis complained. “We live on a bacterial planet,” and evolutionary theory must be able to account for the evolution of the cell, “the fundamental unit of life,” and all that a cell contains: “A minimal cell has DNA, mRNA, tRNA, rRNA, amino acylating enzymes, polymereses, sources of energy and electrons, lipoprotein membranes, and ion channels, all contained within a cell wall, and is an autopoietic [self-regulating feedback] system.” The theory of symbiogenesis does just that, although there are scientists who remain skeptical.

Creationists’ demand for just one transitional fossil is most notably made when it comes to human evolution, for which they claim
there are none. They should have been at the lecture by the University of California, Berkeley, paleoanthropologist Timothy White, which he opened with a prediction made by Stephen Jay Gould in the late 1980s: “We know about three coexisting branches of the human bush. I will be surprised if twice as many more are not discovered before the end of the century.” A glance at the extant fossil record today suggests that Gould was right. There are at least two dozen fossil species in six million years of hominid evolution.

But the bush is not so bushy, says White. The problem lies in the difference between “lumpers” and “splitters” in species classification, and in the social pressures to publish extraordinary new discoveries. If you want to get your fossil find published in
Science
or
Nature
, and you want the cover illustration, you cannot conclude that your fossil is yet another
Australopithecus africanus
, for example. You had better come up with an interpretation indicating that this new find you are revealing to the world for the first time is the most spectacular discovery of the last century and that it promises to overturn hominid phylogeny and send everyone back to the drawing board to reconfigure the human evolutionary tree. Training a more skeptical eye on these fossils, however, shows that many of them belong in already well established categories. White says that the specimen labeled
Kenyanthropus platyops
, for example, is very fragmented and is most likely just another
Australopithecus africanus
. “Name diversity does not equal biological diversity,” White elucidated.

White concluded his talk with a fascinating discussion of the recent discovery of fossil dwarf humans on Flores Island in the Malay Archipelago, located on the outside of Wallace’s Line, meaning that even during the last ice age they could have gotten there only by boat. (White did note, however, that after the 2004 tsunami in this area, people were rescued from large floating rafts
of natural debris, so it is possible that the founding population of Flores humans rafted there by accident and not by design.) Found in Liang Bua cave, the type specimen of
Homo floresensis
was dated at 18,000 years old, meaning that they had to be modern humans because all other hominid species had long ago gone extinct. But with a cranial capacity of only 300cc—about the same size as that of Lucy or a modern chimpanzee—they were able to fashion complex tools (and possibly boats) with tiny brains; the implication is that brain architecture, not size, is what counts for higher intelligence. A second published specimen put to rest the pathology hypothesis that
Homo floresensis
was a microcephalic human. The best evidence, says White, points to insular dwarfing, a rapid punctuation event that led to the shrinkage of these isolated people. Such dwarfing effects can be seen on this and other islands, where large mammals get smaller (like the dwarf elephant) and small reptiles get larger (like the Komodo Dragon). The chances of any living members of this species still existing in the hinterlands of Flores are extremely remote, but some observers have noted that the indigenous peoples of Flores recount a myth of small hairy humans who descend from the highlands to steal food and supplies.

Young Earth creationists have a ready-made answer to this question—the Garden of Eden—and they accept the biblical story of Adam and Eve as factual history instead of mythic saga. IDers, by comparison, avoid all such biblical references and argue simply that there is no evidence for human ancestry and thus there must have been a divine spark of humanity miraculously inserted into one hominid species. The evolutionary story is more complex, says
University of Cambridge professor Peter Forster, an expert in archaeogenetics, who demonstrated how prehistoric human migrations can be traced by mitochondrial DNA (mtDNA) through the maternal line of modern humans.