The History of Astro-Biology as a Science by Keith Cattell

I in my ignorance until very recently, believed that astrobiology started as a recognised science after the second world war possibly as late as the 1970’s.  This was because detailed knowledge of the structure of the universe and detailed knowledge of the beginnings of life on this planet both started at about that time.  In fact, Biology became a science in the late 1800’s mostly due to the work of Darwin and Wallace.  I failed to note that detailed knowledge of a subject is not needed to start thoughts of what might be, to help stimulate investigations as occurred with Biology.

In my work at Wells & Mendip Museum library, I was investigating the books written by Alfred Russel Wallace whose principal claim to fame is to be the partner of Charles Darwin in the discovery of Biological ‘Natural Selection’.  Much to my surprise, I found two books on Astronomy both on the subject of Astro-biology, and I also found that Wallace had a keen interest in astronomy throughout his life as well as being a biologist.  On further investigation, it appears that discussions on ‘Man’s place in the universe’ has been in progress by philosophers throughout the whole of the nineteenth century and indeed before. Wallace’s two books were entitled ‘Man’s place in the Universe’ printed by Cambridge University press in 1903, and ‘Is Mars habitable?’ printed by McMillan press London in1907.  At this age, neither book is still in copyright and so I can quote from them at will.

It appears that many 19th century philosophers considered both the purpose of the universe and the role of Man in it, as one of their key philosophical questions of the time.  During this period most philosophers took what they described as the ‘Pluralist view’, meaning that there were many intelligent civilisations on different planets.  Both these questions became widely public in 1859 on publication of books by Huxley and Whewell both leading philosophers of the time.  Wallace did not reply to these books at the time, as both he and Darwin were deeply involved in collecting the extra the supporting evidence they felt necessary for their own Theory.

However, in his 80’s when he was no longer fit for field work, he took to astronomy which was a subject he felt able to do from his armchair.  This was the first time an eminent Biologist had considered life on other planets.  Wallace was taping into the philosophical tradition of life on other worlds, while trying to give a scientific view to this question.

Wallace took the view that the human mind was special and was the only one of its kind in the Universe.  Darwin had taken the mainstream ‘pluralist’ view and wrote a book on ‘The Descent of Man’ to confirm his views and show what they meant to him.  Wallace’s book ‘a man’s place in the Universe’, started with five chapters on the most recent discoveries in astronomy to confirm his scientific credentials.  The theme of the book was Wallace’s amazement that ‘mild climates and generally uniform conditions had prevailed throughout all geological epochs; and on considering the delicate balance of conditions required to maintain such uniformity, he became convinced that the evidence was extremely strong against the probability of any other planet being inhabited’ (S728 1903b, v-vi).  Very interesting of itself but more so when you note that consistent climate is not an issue considered in the Drake equation.

One of Wallace’s main problems in writing his book was the lack of a scientific definition of life.  Philosophical definitions were of no use.  No other biologist (and only the philosopher Huxley) had tried to make the necessary definition.  Wallace needed this definition to determine the criteria for life to exist.  Wallace and Huxley’s definition of life was based on the existence of protoplasm which is found in in the majority of plant, animal and fungi cells. This only exists,

1. At temperatures between 32 – 104 degrees Fahrenheit;
2. At a minimum air pressure of between 20 – 25% of Earth’s;
3. In the presence of water and carbon dioxide.
   

In 1904 Wallace added an appendix to his book based on the theory of evolution.  Wallace argued that since humanity is the result of a very long chain of modifications in organic life which only occur under certain circumstances, then the chances of the same conditions and modifications occurring elsewhere in the universe were very small indeed.  Moreover, since no other animal on Earth, despite the great diversity of forms, approaches the intelligence or moral nature of humanity, these characters were unlikely to arise in any other form.

Based on what he knew in his day, (very different from what we think we know today,) Wallace had a go at estimating the chances of intelligent life arising on another planet.  The numbers he came up with are quite interesting.  ‘If the physical and cosmical improbabilities set out in the body of my book are somewhere about one million to one, then the evolutionary improbabilities cannot be less than perhaps100 million to one; the total chances of man or a being of equivalent intelligence arising on another planet are 100 million million to one. (S729 1904, Appendix, 334-5). The evolution of intelligence is one of the still unknown factors of the Drake equation, and perhaps there is no better person to estimate it than the person who helped create the modern view of evolution by natural selection. If the estimate of 100 million to one is anywhere near to correct then it is quite possible that we are the only intelligent life form in the milky way galaxy.  We must take great care of ourselves as a species!!

Wallace’s book on ‘is Mars habitable?’ is a reply to Percival Lowell’s book ‘Mars and its Canals’.  Lowell has observations which he says proves that the canals are good evidence in proving habitation by intelligent beings of the red planet.  Wallace gives three separate facts in rebuttal:

1. The mean temperature on the surface of -35 F.
2. The very low atmospheric pressure on the planet surface.
3. The absence of water vapour and water on the surface.

Any one of the above would make the planet uninhabitable let alone to intelligent life.

Wallace in his first book sees an overall purpose to the Universe.
 
‘Lastly, I submit that the whole of the evidence that I have brought together in this book leads to the conclusion that our Earth is almost certainly the only inhabited planet in the solar system; further, there is no inconceivability, no improbability even-that in order to produce a world so precisely adapted in every detail for the orderly development of organic life, culminating in man, such a vast and complex universe as we know exists around us, may have been absolutely required.’(S728 1903b, 306)
 
Although most of us would disagree with Wallace’s conclusions today, I feel confident that this is a good scientific attempt at Astro biology as early as 1903, that is 60 to 70 years before I had thought this possible.  My view of Astrobiology is changed for ever.
 
Note:  The text in italics are direct quotes from for Wallace’s books.