1. Introduction

So much has been written about the various broad theories on the origin of life that it might seem that little else needs to be said. Despite the lack of conclusive or convincing evidence it is generally accepted that life originated on Earth from simple chemicals, although the once heretical view that life originated from space is on the verge of becoming mainstream. In these “musings” I will try and add a perhaps unusual, somewhat historical, perspective on the debate about life, the mystery of which remains as deep as ever.

2. The Origin of Life (Assuming It Had One)

Humans are mentally conditioned to accept that time moves forward to give us beginnings and endings to our experiences. As a result, we cannot escape the idea that life must have started somewhere. The possibility that life had no origin and is eternal is almost impossible for us to comprehend and so we assume that, since the idea has supernatural overtones, we had better find some kind of origin. Pasteur clearly had doubts about this approach when he said:

The current scientific consensus will have nothing to do with such thinking and resolutely maintains that life arose as a one-off act of spontaneous generation (abiognenesis) at some point in the past. This view has a long history; Robert Chambers in his influential, pre-Darwin book on transmutation (i.e. evolution) of 1845 stated that:

The first step in the creation of life on this planet was the chemico-electric operation by which simple germinal vesicles were produced (Chambers, 1845).

While this view has become the orthodox opinion on the origin of life, Alfred Russel Wallace, whose theory of "natural selection" provided the foundation for Darwinism, took the following, different view:

The current popular view of the likely origin of life then depends firmly on a belief in a single act of spontaneous generation; that simple life arose from chemicals here on Earth (they may however originated from space). This proto- life then became more complex, via an evolutionary process explained by the Darwinian and neo-Darwinian syntheses.

However a largely ignored schizophrenic turmoil pervades biology in that while most (but not all) scientists believe that a, one off, act of spontaneous generation created life on Earth in the dim and distant past when conditions differed from what they are at present, these same scientists firmly believe that spontaneous generation is not occurring at the present time. This apparent certainty is however, backed up only by a miss-reading of the experiments and findings of Louis Pasteur in the 1860s.

3. Spontaneous Generation- An Idea Never Adequately Refuted

Our textbooks tell us that, by using his famous swan neck flasks, Pasteur, once and for all, destroyed the belief in spontaneous generation. This is convenient sophism, but it is simply not true. What Pasteur showed was that if a simple nutrient solution is thoroughly boiled and then prevented from being exposed to the surrounding air, it remains sterile until it is exposed to the microbe-laden atmosphere. Pasteur’s contemporary critics pointed out that things might have been different had Pasteur changed the conditions of the experiment by using a more complex nutrient solution, by adding some clay or silicon or by incubating his flask a over range of fluctuating temperatures for an indefinite length of time; the possible permeations which have produced life in Pasteur’s flasks are, of course, endless.

Pasteur’s experiments demonstrated merely that he could kill most microbes by boiling (spores sometimes survived) and that the air is rich in microorganisms which readily contaminate boiled solutions. Although these experiments were essential for the development of the germ theory, the pasteurization of food and the introduction of antiseptic (and later aseptic) surgery, they prove nothing about the existence of spontaneous generation, other than that, if it does occur, it will do so under far more complex conditions than allowed for in Pasteur’s experiments. To his credit, Pasteur pointed this out this simple fact in the following words, which have been ignored ever since:

The possibility then that life may, even at this moment be arising spontaneously in a nearby pond, or perhaps in a deep sea vent, has never been adequately dismissed (of course if it did so, it would likely be consumed by existing life). Shapley Schafer said as much in 1924:

The possibility that life is originating from simple chemicals today goes so much against the current paradigm that is seems impossible to even contemplate; but if this case why should we accept that it happened in this way in the past?

The last serious attempt to demonstrate that life can have a modern origin was by the British pathologist and dedicated evolutionist, Henry Charlton Bastian. Working in the late 1800s and early twentieth century, Bastian believed that life could originate de novo (abiogenesis, or archeabiosis) and from the products of previous life (heterogenesis). His work was never replicated however, and much of it can be explained by the ability of bacteria to grow in apparently nutrient-free solutions, particularly in the presence of added silicon compounds (Wainwright,1997).

Bastian believed that bacteria must have been continuously originating based on the fact that they have never evolved into more complex organisms, despite the passage of long periods of time since life was believed to have originally developed on Earth. This, he suggested demonstrates that bacteria and other microorganisms arise de novo throughout history and that the modern forms we see arose during modern times. Therefore, these modern bacteria have not existed long enough to have evolved into more complex organisms.

Biological textbooks generally ignore the history of ideas and instead make it appear that the first steps towards an understanding about how life arose from chemicals, began with the experiments of Urey and Stanley Miller in 1953. It is worth noting however, that the first experimental steps along this road were taken just after the turn of the twentieth century when Benjamin Moore (Moore and Webster,1913) exposed iron oxide water and carbon dioxide to light and formed formaldehyde, while replacing the iron oxide with nickel carbonate produced sugars as well as formaldehyde.

4. Panspermia

Panspermia is the theory that, instead of life beginning here on Earth, life came from elsewhere. The chief merit of panspermia is that it assumes a large number of possible places where life might have originated (including planets, nebular clouds, and comets) and an extended length of time for it to have happened (Joseph and Schild 2010; Wickramasinghe and Gibson 2010).

It is not clear however, if such increases in opportunity could have really dramatically increased the chances of life originating. Unfortunately, although panspermia may have delivered life to the prebiotic Earth (and continued to do so) the idea strikes some as philosophically unsatisfying as the chemical theory of life’s origin on Earth, simply because it assumes a beginning to life achieved by the same processes which are applied to the Earth–centric theories; this beginning is, of course, imagined to have taken place at some distant time in an equally distant place.

Although most histories of panspermia are restricted to a discussion of the contributions made by scientists like Helmholtz, Lord Kelvin and Svante Arrhenius, the subject has a more interesting and complex origins. Who would believe, for example, that the famous inventor Thomas Alva Edison was a convinced panspermist? Edison argued that (Runes, 1948):

Edison believed in what he termed “life units”, and that:

and:

5. Anti-Panspermia Hysteria: Death to Scientific Revolutionaries

For thousands of years the consensus of "scientific" opinion held that Earth was at the center of the universe, a view endorsed by many western religions. Yet, despite the Copernican revolution, the popular view endorsed by many scientists is that the Earth is still the center of the biological universe. The idea that life did not begin on this planet has long been opposed and ridiculed, as many find the concept frightening and unsettling.

By the beginning of the 1900s, belief in panspermia was gaining ground, based in large part by the work of nobel laureate Arrhenius (1908/2009). However, by the late 1930s, panspermia was being actively attacked by many scientists. Oparin (1938) for example, argued that “we must therefore one and for all, give up the idea that life germs floated towards our earth from the outside cosmic spaces."

Panspermia would however, eventually be dramatically resurrected by the ideas of Fred Hoyle and Chandra Wickramasinge (Hoyle 1982; Hoyle and Wickramasinghe 1971, 1981, 1982, 1985, 1993, 2000; Wickramasinghe et al., 2009), whose theory of cometary panspermia, suggests that not only did life on Earth originate from space (mainly from comets), but that a) this input continues today and may be the source of new viral diseases and b) that evolution on Earth is influenced by genes (naked or otherwise) that originate from space.

Hoyle and Wickramasinghe’s ideas have generally been vehemently opposed by the scientific establishment who more often than not resort to taunts and ridicule more typical of children. Nigel Calder’s attack on Hoyle and Wickramasinghe’s ideas is perhaps typical of this mindset. In his book on comets Calder, (1980), uses a child-like scoring system to dismiss cometary panspermia in the following way:

It is the nature of the history of science for revolutionary thinkers to be attacked by lesser minds. Science is conservative, and religion is well represented in the halls of science.

In 1584, Giordano Bruno, a priest of the Dominican Order, published "Dell Infinito, universo e mondi" ("Of Infinity, the Universe, and the World"). Bruno taught that the stars were just like our sun, that planets must orbit these suns and that sentient beings, just like the humans of Earth, lived on these planets. Bruno reasoned that the universe extended for all eternity, peppered with countless planets, suns, and solar systems. Bruno wrote: "There are innumerable suns and an infinite number of planets which circle around their suns as our seven planets circle around our Sun." On February 19, 1600 Bruno was burned at the stake by the Roman Inquisition of the Catholic Church.

The holding of heterodox views of the origin of life is still considered heresy even today. Not surprisingly, Hoyle, Wickramasinghe, and others have been vilified and attacked. It is a widely believed that Fred Hoyle was denied his rightful Nobel Prize because of his persistence in voicing heretical views on panspermia and the origin of disease from space (Sidarth, 2008). However, this is the fate of revolutionary thinkers; it is the price they pay. The halls of academia, those issuing research grants, most scientific journals and their editors (with the notable exception of the Journal of Cosmology), and the academic scientific establishment routinely fetes lesser thinkers, because they are not a threat.

6. The Microbiology of Panspermia

Life might have originally arrived to Earth from space as a single organism (or proto-organism) or, perhaps more probably, as a mixed population made up of heterotrophs (aerobes, anaerobes and aerobic oligotrophs), phototrophs and chemoautotrophs). The survival of organisms possessing these metabolic strategies would depend on the conditions they meet, such that their survival and establishment would be selected for by the prevailing conditions on Earth.

However, if the panspermic organisms arrived in a meteorite they could bring their own microenvironment with them in which a mixture of, say, cyanobacteria and aerobic heterotrophs might arrive together, the former (following exposure to sunlight) providing oxygen to support the latter. In this case colonisation of the Earth need not, initially, be widespread but may have occurred locally in the face of general, unfavourable physical conditions. A lone aerobic heterotroph might have arrived an Earth devoid of oxygen and therefore would not become established; however, if it arrived with an oxygen-generating phototroph it might have survived on an otherwise oxygen- free, but carbon dioxide sufficient Earth. Perhaps diatoms might act as effective “life capsule” for the transfer of life to Earth (Hoover et al.,2004) as their silica shell would likely protect the internal phototrophic protoplast from environmental extremes, notably UV radiation. It is known that bacteria can co-exist within diatoms cases (Schmid,2003), so it is possible that a heterotroph could be supplied to Earth in a rain of diatoms and survive even in a oxygen-free environment, ready to be released from its diatom shell when the Earth’s oxygen supply improves.

7. Microbes in the Stratosphere-Inbound or Exiting?

Recent studies confirming that bacteria and fungi exist in stratosphere (Wainwright, 2008, Wainwright et al., 2006), lead us to the obvious question –are these microorganisms incoming into this region from space, or exiting from Earth. Most biologists would assume the latter, although the cometary theory of Hoyle and Wickramasinghe is dependent on the former possibility, namely that life is incoming to the stratosphere from space. If microbes can reach the stratosphere from Earth then it is possible that a kind of reverse panspermia occurs, whereby life is ejected from Earth into space, perhaps via the power of solar winds (Joseph 2009).

The ejection of bacteria and other microbes into the stratosphere from Earth will also lead to life being exposed to high levels of UV radiation and this, by increasing mutation rates, might perhaps increase the rate of their evolution of these life forms when they return to Earth.

Dehel et al. (2008) have suggested that electrostatic forces could carry bacteria from Earth into the stratosphere and beyond. This theory like other suggestions which have been made to explain the possible transfer of microbes from Earth to space could only operate for very small (submicron) viable microbial components. Ultrasmall bacteria do occur on Earth and might be transferred to the stratosphere by a variety of mechanisms. However, the presence of bacterial clumps of the order of ten microns has obtained from the stratosphere and it unlikely that such large particles could be elevated from the Earth to this region by any known mechanism.

We have therefore suggested that there exists in the stratosphere a mixed population of microorganisms, some existing from Earth and some (in the form of clumps) incoming from space (Wainwright et al. 2006). The incoming organisms may be uncultureable and contribute to the pool of some ninety-nine percent of the microorganisms on Earth which are presently in this state.

Hoyle and Wickramasinghe’s ideas on the origin of viral diseases from space have been dismissed by epidemiologists on the basis that a virus arriving to Earth from space would not be matched to its human host; incoming viruses may however, be able to exchange genetic information with those Earth viruses which are already matched to humans.

8. Necropanspermia, Necrosymbiosis and the Origin of Life

To date, ideas about panspermia have concentrated on the arrival to pre-biotic Earth of proto-life forms, living bacteria and possibly other microorganisms which then grow and evolve into present day life. Another speculative possibility is that bacteria do not survive the journey through space, but dead, freeze-dried biomass arrives instead; what might be termed “necropanspermia”. This dead biomass would add the fully formed components of life and bacterial degradation products to the prebiotic Earth.

Proto-life that has developed here could then take up these essential components like DNA, cell membranes and mitochondria and develop them into fully formed life, a kind of necrosymbiosis would thereby occur. In this way, many of the complicated stages in the development of life on Earth would be circumvented. Possibly, this necrosymbiosis would occur in drying pools, as the preformed components of life were brought into intimate contact. It would certainly be interesting to determine if cellular components can be taken up and be, activated by simple life forms, although it could be argued that these are already far too complicated for this Frankenstein-like origin of cellular complexity to occur.

9. The Over-Riding Importance of Aerobic Heterotrophy to the Development of Intelligent Life on Earth

Aerobic heterotrophy is the most efficient means by which an organism can gain energy. This metabolic strategy provided the energy to allow simple organisms to move, to become predators, and to evade predation. Predation is the major driving force of evolution, since in the concept of survival of the fittest it leads to the selection which leads to complexity. Such complexity leads to the large efficient brain of Man and has (with the development of an opposable thumb) allowed Man to develop technology, which has lead to computers, books, telescopes manpowered flight and the exploration of the cosmos; all the result of Man’s ability to utilise aerobic heterotrophy. No other metabolic strategy could have provided the energy of the driving force for evolution to intelligent organisms having the ability to explore space. A corollary of this fact is that highly developed, intelligent organisms can only evolve on an aerobic planet.

Whether aerobic heterotrophy arrived in an organism from space via panspermia or developed in situ on earth is immaterial, although its establishment on Earth could only have followed the appearance of the oxygen generating process of photosynthesis. The importance of aerobic heterotrophy lies then in the fact that it is the only growth strategy which can lead to predation and the evolutionary arms race which eventually gave the Earth intelligence.

10. Silicon and Life

The idea championed by many science fiction writers that silicon could replace carbon as both an energy source and the building block for complex biomolecules is extremely unlikely. However silicon may have played a role in establishment of the first bacteria that arose, or arrived to Earth (Wainwright et al.2004). Life uses whatever is at hand, so it would not be surprising indeed to find that the second most common element on Earth is not, used by cells in a more direct way then simply acting as a component of cell walls and diatom shells (Wainwright,1997).

11. Little New Under the Sun

Anyone reading the history of the development of ideas on the origins of life will doubtless be struck how often the basic ideas which we still mull over (and claim as our own) have been considered in the past. For example, a number of recent commentators have suggested that life may be unique to Earth, an idea expressed by Alfred Russel Wallace as follows:

Even the idea that diseases (notably influenza) might originate from space has a long history, as is evidenced by the following quote from Thomas Willis in 1658 (Thompson,1852).

and:

The possibility that comets could influence evolution on Earth (by virtue of their electrical properties) was muted soon after the appearance of On The Origin of Species, as is shown by this quote (Anon. (1861):

The next quote shows that even the idea that comets deliver chemicals to Earth has a long history (Anon, 1855):

Are we then getting any closer to an understanding the origin of life (assuming it had one)? As ever there is much optimism that indeed we are making progress. On the other hand, it often appears as if the origin of life question has become bogged down in ever increasingly sophisticated organic chemistry. The reality is that, despite the egos of some, the existence of life remains a mystery. It is not merely that biology is scratching the surface of this enigma; the reality is that we have yet to see the surface!

And yet, a picture is beginning to emerge: A complete paradigm shift in our understanding of life may be upon us, a revolution we await with bated breath!