Is There a Chemical Origin of the Species? —
Astrochemists search for precursors to DNA in outer space

By Anthony Remijan

Charles Darwin teaches us that by natural selection, the most fit and robust species survive and this leads to a complex chain of events—the formation and evolution of the complex organic systems present on the Earth.

"On the Origin of Species" opened up a new realm of scientific knowledge, arguing that all life-forms seen on the planet today developed through natural selection and evolution.  However, even the simplest of organisms must have had a more humble and fundamental beginning.  Before life ever organized into a single cell, it first needed proteins; and to assemble proteins, it needed to assemble the correct types and number of amino acids. RNA and DNA, the genetic instructions used to create amino acids, are also critical in the development and functioning of all living organisms.

But to truly understand "On the Origin of Species" and the formation of the organic molecules that lie at the heart of life, an even more basic question must be asked: was there a similar "evolution" from smaller, more robust molecules that eventually lead to the molecules that we now call RNA and DNA?  Searching for answers has some scientists looking in a most atypical place: outer space. 

Researchers in a discipline called astrochemistry—the study of chemical elements and molecules in space—are using the most powerful telescopes ever built to search for our molecular origins, led there by a fascinating scientific accomplishment—the famous Miller-Urey experiment of 1953.  Miller-Urey showed that large, organic molecules that form the basis of life on Earth can be formed in an atmosphere of little or no free oxygen.  The result presents an interesting dilemma because it is becoming more evident that the early Earth did not have the low oxygen environment necessary to synthesize these biologically important molecules. 

Unlike the oxidizing atmosphere of primitive Earth, interstellar space is a highly reducing environment, one that is rich in hydrogen and is conducive to the formation of large, organic species that may be the chemical precursors to RNA and DNA.  Evidence of this comes from infrared views of the space dust around newly forming stars.  Looking at these sources of material, we find the most complex of interstellar molecules.  In parts of the Orion nebula, as well as regions of high-mass star formation in our own Milky Way Galaxy, lies a chemistry that is producing molecules from vinegar (acetic acid) to antifreeze (ethylene glycol).

From spectroscopic research conducted via remote sensing at radio telescopes, we now know that interstellar space—the space between stars—which only a few decades ago was widely believed to be hostile to organic chemistry and chemical bonding, contains an astonishingly rich inventory of both familiar and exotic molecules. Furthermore, these molecules are found throughout the universe in giant gas clouds relatively close to Earth in our own Milky Way galaxy, and in external galaxies billions of light years away.

The inventory of interstellar molecules currently stands at 154.  Many are common terrestrial compounds such as water and ammonia, and larger species including alcohols, aldehydes, ethers, carboxylic acids, amines and nitriles.  But an equally large number are exotic by terrestrial standards, generally unknown or unfamiliar to chemists, including both positively and negatively charged molecular ions, radicals, carbenes and their energetic isomers, unusual metal-bearing species, and highly unsaturated organic species, including bare carbon clusters.

It is apparent there is a complex chemistry in space leading to a suite of organic material.  However, the question remains: how do larger, organic species that are the possible precursors to amino acids, or even amino acids themselves, assemble into a self-replicating molecule like RNA?  Is there a preferred "natural selection" that will not only lead to the formation of larger molecules but also eliminate smaller, less robust molecules that cannot survive the harsh environments of interstellar space?

For example, did the first polyatomic molecule detected in space, formaldehyde, evolve into acetone—the main solvent in household nail polish removers or urea (found in the excretion of all terrestrial vertebrates) via the principles of evolution outlined by Darwin?  As intricate as these species seem, they are exceedingly simple compared to a strand of RNA.

One idea, called the "RNA world hypothesis," proposes that life in our world first was based on RNA, which evolved into current life based on DNA.  It argues that RNA is the evolutionary remnant of the RNA world.  DNA, through its greater chemical stability, took over the role of data storage and proteins became the specialized catalytic molecules that fuel the development of life.  Yet there are nearly infinite possibilities of arranging atoms, then molecules, before a species resembling RNA is ever formed.  So while advances in astrochemistry continue to find even more molecular complexity in the universe, we still may never determine how these benign and humble beginnings to organic chemistry manifested themselves into the complex biological systems of today.  However, we continue to search for the answers to our molecular origins by looking out into the universe.

Anthony J. Remijan is an assistant scientist at the National Radio Astronomy Observatory in Charlottesville, Va.  He is a commissioning scientist who helps devise procedures to test and verify the Atacama Large Millimeter/submillimeter Array, a system of 66 radio telescopes that combine their signals to simulate a single, expansive telescope, located on the Chajnantor plateau in the Atacama Desert of northern Chile.  The project is the most ambitious ground-based telescope currently under construction.  Remijan has taught in several educational settings, including the University of Maryland-University College, Prince George's Community College, Parkland College and Illinois State University.  He promotes the sciences of astrochemistry and astrobiology through frequent public speaking and holds a Ph.D. in astronomy from the University of Illinois at Urbana-Champaign.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

Evolution A Starry Archetype
Astronomers adapted Darwinism to create organizational framework that describes cosmic evolution

By Dr. David DeVorkin

Strictly speaking, mainstream 19th and early 20th century astronomers were less influenced by Darwinism than they were a part of a larger movement to think in terms of evolutionary change or "universal evolution."  For astronomers, this meant that systems of planets and stars, and stars and planets themselves, were not static over time, but changed through gravitational processes, the conversion of gravitational potential into motion, light and heat.  It was French mathematician and astronomer Pièrre Simon Laplace's Nebular Hypothesis that galvanized 19th-century thinking, especially in the United States, where the term evolution was quickly appropriated to mean evidence of change in the heavens: of planets, stars and systems of stars.  If Darwinism was linked to astronomical progress, it was more than not derided; in 1871 one writer scoffed at the very idea that life existed on the Earth at a time when, according to Laplace, the Earth was still in nebular condensation. Objections to Darwinism then and for the next few decades, indeed dealt with time scales more than anything else as Joe D. Burchfield and others have examined.

By the late 19th Century, it was George Darwin, not Charles, who offered inspiration to American astronomers. Darwin's second son and fifth child explored tidal evolution of rotating fluid masses, i.e. stars and planets. His teachings regarding the high and low tides of the Earth's solid body, which are very similar to the oceans' high and low tides, informed all subsequent generations about the planet's dynamism. Princeton University astronomer Charles A. Young observed in 1884 that George Darwin's theory of tidal evolution "opened a new field of research, and shown the way to new dominions." Not only did it shed light on the dynamical history of the Earth-Moon system, but, Young implied, it offered a new way to organize research.

For Young, and contemporary Victorian astronomers like Norman Lockyer, the English scientist and astronomer who discovered helium and founded the science journal Nature, universal evolution included studying how the very elements of physical existence formed and grew and could be destroyed during the life cycles of stars. Young encouraged his most illustrious student, Henry Norris Russell, to think in evolutionary terms and hold a naturalistic view of the universe, one of continuous development, presently acting and not confined to original cause. These elements indicate Darwinian thinking. Russell's research, leading to the Hertzsprung-Russell Diagram, the primary descriptive playing field for 20th century stellar astrophysics, was indeed stimulated by a neo-Lockyerian theory of stellar evolution.

A contemporary of Russell's who played possibly the most visible role in America establishing evolutionary thought as the organizing principle for research in astronomy was George Ellery Hale. The driving force behind the establishment of Yerkes Observatory, operated by the University of Chicago in Williams Bay, Wis., one of his first major programs there was to study red stars in the hope that they would lead finally to a "systematic scheme of stellar evolution on spectroscopic observations…" Hale made the observation in Yerkes's Decennial Publications in 1903.

Evolution as Hale understood and expressed it was not Darwinian, but he appropriated Darwinism as a symbol and as an organizing principle. In 1902, he told a popular audience that: "It would be difficult to overestimate the effect which the doctrine of evolution has wrought. The principle of orderly and harmonious development which it embodies has found application, not only in explaining the wide diversity of organic species, but in unifying the events of history, in elucidating the origin of language, and in throwing light on difficult questions in every department of human knowledge."

Over the next decade, Hale used the National Academy of Sciences as a platform to explore what all the sciences could say about the evolution of matter, stars, planets, life, man and society. Among Americans of the intellectual generation following Hale and Russell, leading into the mid-twentieth century, possibly the most ardent proponent of Darwinism—in the manner Hale expressed it—was Russell's former student, Harvard College Observatory director Harlow Shapley, who, unlike the majority of his contemporaries, included biological thinking in his essays on cosmic evolution. As historians have noted, Shapley's 1958 book "Of Stars and Men," a collection of earlier essays and lectures, set the stage for modern American writers—from Sagan to Chaisson—to explore the rich rhetorical landscape made so compelling by Charles Darwin, indeed a popular symbol and organizing principle of modern astronomy.

Dr. David DeVorkin is senior curator of history of astronomy and space sciences at the Smithsonian National Air and Space Museum in Washington, D.C. He is the author/editor/compiler of nine books and more than 100 scholarly and popular articles including "Hubble: Imaging Space and Time" (2008); "Beyond Earth: Mapping the Universe"; "Henry Norris Russell: Dean of American Astronomers"; and "The American Astronomical Society's First Century."

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

The Heavenly Origin of Evolution
Natural selection viewed as logical extension of widely-accepted nebular hypothesis

By Ron Numbers

At the risk of oversimplifying a complex historical narrative, I would like to argue that the history of evolution did not begin in 1859 with Charles Darwin's "Origin of Species," but with the publication in 1796 of Pierre Simon Laplace's so-called nebular hypothesis. In 1798, Laplace, a distinguished French mathematician and astronomer, first suggested that the planets were created from the atmosphere of the sun, which, because of its heat, originally extended beyond the orbit of the most distant planet. As this atmosphere condensed, it abandoned a succession of rings—similar to those of Saturn—in the plane of the sun's equator. These rings then coalesced to form the various planets, similar to the way satellites or moons developed from planetary atmospheres.

Later, after William Herschel, a German-born British astronomer discovered interstellar clouds of dust and gas, called nebulae, Laplace argued that the primitive condition of the solar system resembled a slowly rotating hot nebula. This speculation attracted little attention in the English-speaking world before the 1830s, when several books brought it to the attention of the reading public.  It featured significantly as the beginning of the evolutionary account in the sensational "Vestiges of the Natural History of Creation" (1844), an anonymous work that introduced the idea of evolution, inorganic and organic, to tens of thousands of readers.

By the 1840s and 1850s, the nebular hypothesis was being taught in American colleges and embraced by leading biblical scholars as describing God's method of creating the solar system. Charles Hodge of Princeton Theological Seminary, arguably the most influential American theologian in the middle third of the century, concluded the first verses of Genesis "clearly intimated that the universe, when first created, was in a state of chaos, and that by the life-giving, organizing power of the spirit of God, it was gradually moulded into the wonderful cosmos which we now behold." For him, development from preexisting material clearly fell "within the Scriptural idea of creating." The solar system may have been created by natural laws, but they were God's laws.

By 1859, large segments of American Christians—one contemporary estimated a half—accepted the scientific evidence for an evolved solar system, as well as the great antiquity of life on earth. They had come to think of creation not in six days but over immense periods of time. And, just as important, they had become convinced that science required explaining natural phenomena naturally, not miraculously.

Not surprisingly, a number of the early proponents of Darwinism appealed to the successful accommodation of the nebular hypothesis to justifying accepting organic evolution. Brown University biologist A. S. Packard, for example, noted that the acceptance of the nebular hypothesis led almost directly to the question of "whether plants and animals share in their process of evolution." Numerous others, scientists and clergy alike, made much the same point. For such people, as geologist Clarence King observed, Darwinism was simply the last link in the chain of evolution that began with the nebular hypothesis.

Ron Numbers is a prominent scholar on the history and relationship of science and religion, having co-edited two anthologies on the subject. He is a 2008 recipient of the History of Science Society's George Sarton Medal. Numbers currently is Hilldale and William Coleman Professor of the History of Science and Medicine at the University of Wisconsin-Madison.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.