The sleeping chironomid and the theory of panspermia

An enduring interest of mine for nearly 40 years, has been comparative studies of larvae of three endemic species of flies inhabiting transient rain pools in tropical Africa (H. E.  Hinton, 1968).  In some ways, the most extraordinary of these is the larva of the chironomid midge with the cumbersome name Polypedilum vanderplanki, originally brought to our attention by H. E. Hinton  (Hinton, 1951, 1968). What chiefly captured his imagination was the ability of this complex metazoan life form to lose virtually all tissue water and survive in a desiccated state, seemingly indefinitely. Called cryptobiosis, this condition is so clearly an adaptation to the transient nature of its habitat that it has lead to much bold conjecture. Especially relevant is the possibility of  us humans  exploiting suspended animation for the exploration of space (Oleg et al., 2010), including the use of larvae to seed life to alien worlds. A fertile imagination might go further and suggest that the process of natural selection and evolution, starting with any ancestor of man, would eventually lead to Homo sapiens, and hence to the colonisation of space by man. This, essentially, is the theory of Directed Panspermia championed by Francis Crick (Crick, 1982).

In a staff seminar I gave to the zoology department at my university many years ago, I recall mentioning the Hinton/Crick hypothesis. During the discussion that followed my paper, a senior colleague, Alec Panchen, questioned the use of P. vanderplanki as colonist for man on the ground that it could never have worked because P. vanderplanki is not an ancestor of H. sapiens. This seems a reasonable objection but is it correct? I will here attempt to show that it may not be because it ignores decomposition, among other things. The purpose of this essay is to return to Ale's comment. What I wish to examine here is whether metazoa like P. vanderplanki larvae, under novel selective pressures encountered on a strange world, could ever lead to the emergence of Homo sapiens. Because P.vanderplanki is not an ancestor of man, this, at first sight will seem a nutty, even silly idea. To discuss the point, I return to the concept of Directed Panspermia.

At the outset, to confine conjecture to manageable limits, I greatly simplify the whole matter of seeding life elsewhere. In particular I adopt Conway Morris’s simplifying assumption that the course of evolution is not composed of infinite possibilities but instead, if rerun, will follow a similar path ending every time at the same place. He confined his discussion to earth but I am going to adopt the same reasoning for any planet suitable for life. With these assumptions in place and limits in place we are ready to question the purpose of any attempt to seed life elsewhere. There would seem to be two possible aims. First, purely for reasons of intellectual curiosity – to spread that amazing phenomenon ‘life’ where it is not yet present and where it might never originate on it own. Such an intellectual basis finds strong appeal to man and might lead to the seeding of life being attempted some day fairly soon. The possibility of seeding life elsewhere is not a trivial undertaking. Just because we can do it, should it be done? In fact I read today in Nature that it has already been done by seeding live tardigrades to the moon (Nature 2019). The purpose of this act is not given. 

A second possibility is much more problematic, that is the seeding undertaken in order to lead to the emergence of our species elsewhere. Crick calls this Directed Panspermia. There seems a tacit assumption in both the writing of Hinton on P. vanderplanki and Crick that the desired result would be achieved whatever the details of natural selection encountered.  Let’s examine this aim in more detail; it exposes some interesting difficulties.

First is the vexing question of the type of seed that should be chosen for this bold venture. Despite science fiction stories, it is very difficult, actually nearly impossible, for complex species like us to make the journey, even within our own solar system. It would be much better to send some simple organism capable of cryptobiosis, like P. vanderplanki, rotifers, tradigrades, resurrection plants or bacteria. In cryptobiosis they can travel vast distances in space and quickly take up active life and adaptive radiation when suitable conditions return.

Whatever the seed chosen, whether bacteria as favoured by Francis Crick or the metazoa and metaphyta listed above, whether ancestor of man or not, there is something important that appears to have been overlooked. I refer to decomposition, even if only by autolysis. What might decomposition following inevitable death of seeds lead to? This is where things get interesting because decomposition must lead to the release of DNA and RNA and possibly also to the release of the bases; adenine, guanine, cytosine and thymine which comprise the alphabet of DNA and RNA, the common ancestors of all life on earth. These nucleic acids free in the oceans of an empty world, in a ‘warm little pond’ or in volcanic fumaroles and so on, open up the possibility of multiple lines of evolution and adaptive radiation parallel to that of the original seed. Crick considers that any such free stating blocks of life will be immediately destroyed by competition but this conclusion applies to earth where conditions suitable for the origin of life no longer exist. Such considerations do not apply on lifeless worlds wherever there are conditions suitable for life. So we begin to see the possibility of a complex ecosystem eventually emerging, with the parent seed evolving along with lines of evolution starting with DNA/RNA. Therefore adding decomposition introduces a greatly inflated range of evolutionary possibilities reducing the strength of Alec’s reasoning. So P. vanderplanki might serve perfectly well as a seed after all. Indeed, following this line of reasoning, do we need a living seed at all. Would not a simple package of DNA do? 

One final point I wish to make is that, baring extinction, evolution does not end with H. sapiens as we know it but is a stage in an ongoing evolutionary process. So, wherever man evolves, on earth or on an alien world, might it lead to something that, from our present perspective, we would not recognise or even like, such as the creature in the painting below by the polish artist Zdzislaw Beksinski. This would certainly put a fly in the ointment of the aims of Directed Panspermia.

references

Crick, F. (1982). Life Itself. Its Origin and Nature. London: Macdonald and Co.

Hinton, H. E. (1951). A new chironomid from Africa. Proceedings of the Zoological Society of London., 121, 371-380.

Hinton, H. E. (1968). Reversible suspension of metabolism and the origin of life. Proceedings of the Royal Society, London (B). 171, 43-47.

Oleg, G., Tetsuya, S., Valdimir, S., Nataliya, N., Manabu, S., Ludmila, M., et al. (2010). The sleeping chironomid: an insect survived 18 months of exposure to outer space. Paper presented at the 38th COSPAR Scientific Assembly., Bremen, Germany.
Nature (2019). Moon bears. Seven Days. 572, 289.