Science: Evolution Before Life

Some time, some place in the dark backward and abysm of time, the first "living" thing was created, and evolution began. But even the simplest organism is made up of enormously complicated chemical compounds. How were these compounds produced in the slow aeons of the world's beginnings? Last week Dr. Melvin Calvin, professor of chemistry at the University of California, described some probable steps in the strange, speculative science of chemical evolution that led to the first glimmer of life.

Most pre-evolutionists agree, said Dr. Calvin, that life first appeared something like 2 billion years ago when the earth's atmosphere was dominated by hydrogen compounds such as methane, ammonia and water vapor. Such simple organic compounds as acetic acid and glycine (an amino acid) are formed in the laboratory when ultraviolet light or electric sparks pass through such mixtures. Presumably, solar ultraviolet and natural lightning would do the same in nature.

Young Earth. While the young earth was still raw some 5 billion years ago, Dr. Calvin believes, great quantities of these relatively simple organic compounds were formed out of the nutritious atmosphere. But, he points out, the very agents (light, radiation) that form these compounds tend to break them down, and thus produce equilibrium far below the living level. Obviously, some other processes were at work.

One of them was probably autocatalysis—the process by which a substance, as soon as a little of it is formed, speeds the formation of more of itself. This process is common in organic chemistry. Many molecules important to life are autocatalytic, and in the soupy ocean and suffocating atmosphere of the young earth their concentration would tend to increase. The porphyrins, for example, which are related to the hemoglobin of animal blood and the chlorophyll of green plants, are autocatalysts.

Many of these simple organic compounds have large, flat molecules that tend to drop out of even a very dilute solution. When they precipitate, these flat molecules produce layered structures, like playing cards scattered thickly on the floor. But they arrange themselves more neatly than cards do. Their edges tend to stick together, and thus the molecules build up into orderly stacks. The porphyrins do this, and so do the components of DNA (deoxyriboenucleic acid), the heredity-carrying substance that dominates life on earth.

Nameless Progenitor. Dr. Calvin sees chemical evolution fairly clearly up to DNA, but he cannot say just when the spark of life appeared. The best test of life is that the organism can make replicas of itself, taking as building materials the simpler molecules in the medium around it. The first organism to pass this divide between the living and the inert may have been a single complex molecule or a large cluster of them. This tiny, nameless primogenitor of all living matter may have used some primitive kind of photosynthesis to reproduce itself. Or perhaps it merely picked up smaller molecules in a series of random accidents. Dr. Calvin does not know.