CP-2156 Life In The Universe


IV- Evolution of Complex Life in the Galaxy.


(Stenonychosaurus inequalis, Model in Foliage courtesy of National Museum of Natural Sciences, National Museums of Canada).

(Stenonychosaurus inequalis, Model in Foliage courtesy of National Museum of Natural Sciences, National Museums of Canada).



[209] The Darwin-Wallace theory of biological evolution through natural selection makes the adaptability of life forms to their environment the factor most important to their survival and success. It follows that environmental change ought to result in faunal and floral change, and that a particular environment ought to favor certain faunal and floral characteristics over others. On a superficial level, the truth of these propositions is obvious to any careful observer of Earthly life; indeed Darwin was led to his theory when he drew exactly these conclusions from his empirical studies. But on a more fundamental level, the relationship between life's environment and biological evolution, even after a century of success in post-Darwinian paleontology and genetics, remains obscure. We cannot predict, even qualitatively, the rate and direction of evolution from a knowledge of environmental parameters and their history.

Our lack of understanding can best be illustrated by posing some questions that we cannot answer: what is the effect on the rate and direction of evolution of gross planetary characteristics such as orientation of spin-axis, rotation rate, atmospheric composition, incident stellar energy flux, and size of contiguous land masses? How do changes in these characteristics influence evolution? Can cataclysmic cosmic phenomena (e.g., nearby supernovae, asteroid impacts) cause mass extinction events such as those of the Permo-Triassic and Cretaceous-Tertiary boundaries? Do mass extinctions change the rate of gross evolutionary trends such as the development of an increasingly sophisticated central nervous system? Only when such cause-and-effect relationships are understood will it be possible to develop a quantitative model that can predict the gross evolutionary pattern once the environmental history has been specified.

Research aimed ultimately at developing such a model is important today for more reasons than mere scientific curiosity. At stake is nothing less than our ability to understand the nature and distribution of life in the Universe about us. It will soon be possible to discover other planetary systems and to measure the gross characteristics of their components. But we must understand what an environment portends for evolution if we are to be able to determine from such measurements whether a given planet is likely to [210] support life and, if so, what form that life is likely to take. And it is of special interest to identify systems with planets on which intelligent life may have evolved since we have the ability to detect manifestations of technological activity, such as radio signals, if only we knew in which direction to look.

It would seem that today we have for the first time capabilities that should make discernible the causal relations between life's environment and evolution. Our abilities to study the environments of Earth's sister planets at first hand and to date accurately the rock record on these bodies, as well as on Earth, ought to allow us to determine whether events in the history of life on Earth were related to environmental changes, such as an increase in solar luminosity or a decrease in Earth's rotation rate. Improved knowledge of biochemistry and genetics should be able to tell us what possibilities are open to evolution and what paths are barred, both very generally and under specific environmental constraints (e.g., temperature, moisture availability, surface gravity). Modern techniques for studying ecological systems in the field can highlight the ways in which the environment and changes therein influence survival prospects. And modern data-processing capability makes possible the modeling of complex interactions, such as energy flows, in ecological systems.

These approaches are not likely to be exclusive. The papers in this session present the thoughts of some of our leading scientists on various aspects of the relation of environment to evolution. It is hoped that their efforts will not only bear fruit, but will also stimulate the research of others.


Dr. Mark A. Stull
Extraterrestrial Research Division
Ames Research Center (now practicing law in Maryland)