TERRESTRIAL LIFE IN SPACE

Chapter 6J

TERRESTRIAL LIFE IN SPACE

If a man hangs upside down for many hours, blood will rush to his head, his breathing will be impaired, and he will die. To prevent such a fate, evolution has provided us with means for telling which way is up. In mammals this means includes the otoliths of the middle ear, sophisticated muscular-skeletal sensing devices, and the coupling of eyesight in conjunction with all these organs to the brain. This detection of gravity is no less important to a plant, which needs to send its roots into the ground in search of nutrients, and its shoots into the air in search of gases and sunlight. Since in orbit gravity is practically absent, many experts predicted that the perceptual and physiological disorientation would lead to heart trouble, depression, and mental impairment. The severity of these and other disorders would surely make manned space flight impossible.

The march of events has confounded all these dire predictions about the fate of humans and other forms of life in space. Nevertheless, space flight does affect living things in a variety of ways. Caution has been called for, and caution has been exercised. The result has been a large body of research -- mostly clinical research --aimed at insuring the safety of astronauts and at establishing the degree to which humans can adapt to the low gravity and high radiation of space. This body of research does not include all the biological investigations carried out in space, but its prominence has led to a distortion of the significance of doing biology in space.

Some observers have thus concluded that biological research in space makes sense only if we are planning to continue manned space exploration.[1] Of course, they say, we have to know what space does to a human body if our astronauts are going to spend long times in that environment. And if plants and animals are to be an integral part of man's adventure in space, we will have to learn about how they are affected also. In that spirit I could argue as follows. If other space science is worth doing, as I have shown in the previous two and a half chapters, and if a manned space program greatly advances the cause of space science, then such a program is also justified.

Settling for this argument, however, keeps us from subjecting space biology to the same scrutiny we have put the other space sciences through, and we would thus tacitly accept the assumption that space biology has little to offer on its own. Now, there are experts, even in biology, who make precisely that assumption, and my immediate task is to examine their reasons.

Part of the problem, as I said earlier, is one of image. For instance, NASA has placed great emphasis on vestibular research, for the function of the inner ear is deeply connected with motor and perceptual systems. Since motion sickness is probably the result of vestibular disorientation, research in this area has shown great concern for the welfare and effectiveness of the astronauts. And thus people who want to turn down support for space biology often say that it is just more research on why the astronauts throw up.[2]

But such remarks are neither accurate nor fair. In space we can ask questions about life that are not possible otherwise. In particular we can study the role of gravity in the structure and the development of organisms. In a space station, for example, we may choose at will the amount of gravity to which plants and animals will be exposed. This can be done merely by the use of a centrifuge. When the centrifuge is off, the gravity is close to zero. And, when it is on, it makes the container go in circles, subjecting the object under study to whatever linear acceleration we wish. To a plant or an animal such acceleration is the equivalent of a gravitational force acting on it.[3] Our main interest lies in the range between 0 and 1g, since there we may want to study not only the perception of gravity but perhaps even the role that gravity has played in evolution. By experimenting in that range we may be able to determine gravitational thresholds of biological importance; that is, we may determine the minimum level at which gravity can be detected and at which it becomes a significant factor in physiological or developmental functions.

But are these important questions? Are there any reasons to suspect that gravity will in fact turn out to be a significant biological factor? At first sight there certainly are reasons. Gravity is all-pervasive in our planet; it is not hard to imagine that life took advantage of its presence to favor some avenues of evolution over others. As Galileo noticed as early as 1638, how much an animal weights depends on how well its bones can support it.[4] Thus the anatomical structure of an animal -- or a plant for that matter -- depends on gravity. In a planet with lower gravity, we may find much taller animals and more symmetrical trees (the symmetry is often broken because slight differences in mass in the branches weigh the tree down in different ways; the more the gravity the more pronounced those differences become in the development of the tree --see Figure 6).

Nor is it difficult to imagine that what is true of anatomy may also be true of physiology and other areas of biology. Indeed the absence of gravity (or, rather, being in microgravity) leads to a shifting of body fluids, and such shifts affect the cardiovascular system in humans. As a result we may have an opportunity to study how the functioning of the cardiovascular system -- or rather its malfunctioning -- is connected with the deterioration of muscles. This of course is a matter of potential significance for the general population, especially for the elderly. Moreover, in microgravity we no longer need many of our big muscles to support us. As a consequence the body begins to reduce its levels of calcium and other minerals needed to strengthen the muscles. This presents a big problem for astronauts, whose bones become weak and brittle. On the other hand, their problem may give us a chance to study the connections between bone and mineral metabolism and endocrine action. Here the adverse reactions of astronauts to weightlessness resemble the symptoms of some diseases on Earth. Space physiology thus offers a chance to investigate the underlying mechanisms of such diseases.[5] Similar consequences may be derived from the much belittled vestibular research (for example, the study of Meniere's disease, an affliction of the middle ear characterized by deafness and vertigo).

By all appearances, then, space biology proper illustrates once more that exposing our ideas to unusual circumstances leads to their transformation, and that the transformed ideas lead in turn to new kinds of practical applications. Furthermore, the possible transformation of our ideas is not limited to physiology, as the following examples indicate.

The kind of examination made possible by controlled, variable gravity is of fundamental importance in botany. As I mentioned earlier, the perception of gravity directs the way a plant grows. Reaction to sunlight may have been suspected as the main factor some time ago--but no more. For in the microgravity of space roots grow out of the ground into the air and the shoots are generally disoriented in spite of the constant illumination from the top. Gravity is obviously the main factor in the case of the roots; shoots require both gravity and illumination. But how do plants recognize gravity? They have gravity receptors, and thanks to space research we are beginning to understand what those receptors are.[6]

This possible contribution of space to a seemingly fundamental issue in botany may lead to similar contributions to other branches of biology. It is also interesting, for example, to investigate the ways in which different animals detect gravity. Embriology, the study of individual development, may also benefit from experimentation in space. So far there are indications that gravity may play a role in the axial orientation of amphibian embryos (which is a factor in the normal development of amphibians) and perhaps also in that of birds.[7]

Nevertheless the importance of space biology proper continues to be discounted. It is clear to all parties concerned that judgements of the value of space biology proper should be made relative to what could be accomplished if the money, talent, and effort were directed elsewhere in biology. And the general feeling is that we could do much better.

This feeling goes hand in hand with the general perception that the biological research done in space is not of very high quality. Such a low evaluation is reinforced by two further notions. The first notion is that all the abnormal effects of gravity take place at the systems level, not at the level of cells. Thus, for example, since we do not need strong bones for support, we lose calcium; this loss may in turn have unusual effects on several physiological functions, and so on. But with appropriate exercise and diet we may preserve our need for strong bones; therefore the system imbalance will be largely corrected and the unusual circumstances will be kept to a minimum. As a consequence, the biological significance of space will also be kept to a minimum.[8]

The correctness of this notion is presumably buttressed by experimental and theoretical considerations. Most space biologists themselves have interpreted the results of many cellular experiments as indications that cells are largely unaffected by gravity.[9] And this conclusion comes as no surprise, since it accords with what theory has led them to expect: Cells are small enough that the force of gravity means little when compared to the electromagnetic forces so crucial to the chemical bonds of life.

At the molecular level gravity should be even less significant. And this brings us to the second notion at play. Many biologists are inclined to believe that what really matters in biology takes place at the molecular level or close to it; therefore, as far as they can tell, controlling gravity as a factor is not going to bring us great breakthroughs.

I think that the general feeling against the value of space biology proper is misguided. To see why, it is necessary to show why the concerns just expressed are mistaken. I will take them up in order.

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[1] This emphasis is exemplified by the attitude of the National Academy of Sciences. In a report entitled "Space Station Needs and Characteristics," (May 1983) The Committee on Space Biology and Medicine of the Academy's Space Science Board said, "...the main scientific justification for a Space Station Biomedical Laboratory is laying the physiological groundwork necessary for launching manned space flights of long duration sometime in the next century… Although [the zero-g] environment would provide also an opportunity for carrying out some fundamental biological research, we do not believe that this aspect can be a major consideration in justifying the Station." (p.4) The fundamental biological problems recognized by the academy are the perception of the gravitational vector by plants and the determination of body axes in metazoan development (chiefly in amphibians and birds--both problems are discussed in this chapter). It seems that just two problems are not enough, or perhaps these two are not fundamental enough, in the eyes of the academy.

[2] Scientists who oppose manned exploration on the grounds that it detracts from real space science often concentrate their fire on space biology. Writing in Nature, R. Jastrow said that the Space Station would be a tragedy, "...another two decades of original research on why astronauts vomit." (Quoted in Science Digest, May 1984, p.142).

[3] The main difference is that coriolis forces may be more pronounced in centrifuges.

[4] A good source for the state-of-the-art research on how gravity affects life can be found in the proceedings of the annual meetings of the IUPS Commission on Gravitational Physiology, published as supplements to The Physiologist. See particularly Vol. 25, No. 6, Dec, 1982, and Vol. 27, No. 6, 1984. For biology in the Space Shuttle see the series of reports from Spacelab entitled "Life Sciences," Science, 13 July 1984, Vol.225, pp.205-234. For possible future experimentation see The Fabricant Report on Life Sciences Experiments for a Space Station, J.D. Fabricant, ed., a publication of the University of Texas Medical Branch, Galveston, Texas, 1983.

[5] Paul C. Rambout, "The Human Element,: in A Meeting with the Universe: Science Discoveries from the Space Program. NASA (1981), p. 142. In renal and electrolyte physiology also, space brings about many interesting variations from normal.

[6] See the gravitational physiology supplements to The Physiologist cited above. Also see Experiments on Plants Grown in Space, Supplement 3 to Annals of Botany, Vol. 54, (Nov., 1984). For an assesment and long range planning of plant gravitational research see "Plant Gravitational and Space Research," Report of a Workshop held April 30-May 2, 1984 in Rosslyn, Virginia, a Publication of the American Society of Plant Physiology, 1984.

[7] See, for example, S. Kochav and H. Eyal-Giladi, "Bilateral Symmetry in Chick Embryo Determination by Gravity," Science, Vol.171, 1971, p. 1027; and A.W. Neff and G.M. Malacinski, "Reversal of Early Pattern Formation in Inverted Amphibian Eggs," in the Proceedings of the Fourth Annual Meeting of the IUPS Commission on Gravitational Physiology, op. cit., p.119.

[8] Although similar research could still be carried out on animals.

[9] For this general conclusion about the space environment, see G.R. Taylor, "Cell Biology Experiments Conducted in Space," BioScience, Vol.27, p.102. For an influential experiment on cultures of embryonic lung cells, see P. O'B. Montgomery Jr., et al, "The Response of Single Human Cells to Zero-Gravity,"in R.S. Johnston and L.F. Dietlin, eds., Biomedical Results from Skylab, NASA SP-377, 1977, p.221.