Some of you out there who know me better as a rock guitarist (of Queen, et al.) may also know that I have elected to go back to Imperial College London, after an absence of 30 years or so (I was busy!), as a post-graduate student, re-registering for the Ph.D. in astrophysics that I began around 1970. Laying my cards on the table, I am very aware of my essentially amateur status, but eager to catch up on the last 30 years of astronomical research. I get to go to some pretty high-powered seminars, plus enjoy the privilege of being around scientists who are in touch with the most distant surface of the bubble of knowledge that we are pushing out into the observable universe. And this gives me wonderful opportunities for insight.

But I have an extra secret bonus. I have taken to sneaking into my daughter’s undergraduate biology lectures. The question of life was the part of our journey in writing the book “Bang!” that put the three of us most at odds – and we maintain a healthy dialogue as time goes by. So I find myself drawn to anything that can throw light on the murky question, Are we alone? I’d just like to pass on a few thoughts from a recent series of lectures (by Professor Tim Barraclough) that thrilled me, given by the biology department at Imperial College under the title, “What is Life?” The answer, brilliantly put, was in fact, “life is evolution,” and “evolution is life.” Let me explain.

I think most people now know that the job of mapping the human genome was recently completed – the genome being effectively a complete “recipe” for a human being – a set of instructions or decisions, if you like, about how to put the basic atoms of nature into the right order. The genomes for many other animals have now been tabulated, giving great insights into which animals are most closely related in their family histories. This is where we meet the magic of evolution.

The genomes give clear clues as to how one kind of animal, under the influence of natural selection, can evolve into a different species. By the way, it is clear here that all the animals alive on the planet today are the most highly evolved examples of their particular line of descent – otherwise they would not be here. Human beings have no right to consider themselves any more special than any of our fellow survivors on the planet. And as far as being the dominant species, there is no question that bacteria, not us, are way out in front – in their numbers, in the number of environments they inhabit and even in total mass.

The lecturer asked us how we would define life. What distinguishes something that is alive as opposed to something inanimate? Many answers came up; movement, respiration, consciousness, the ability to replicate, the assimilation of energy, self-organization Рthe property of contradicting the second law of thermodynamics by making ourselves more ordered (reference Schr̦dinger) Рmetabolism, birth, death, communication and the ability to evolve. All of these were accepted as valid signs of life. But is there a single thing that characterises life?

The lecturer reminded us that natural selection can take place only if a) the organism can reproduce itself, and b) the reproduction is subject to mutation – i.e., “mistakes” are made in the replication so that the offspring is not quite identical to its parents. It is only these mistakes that, by rendering the animal more successful in the struggle for survival and reproduction, can drive evolution forward. Of course, we are all aware that in some quarters in the United States, shockingly for the scientific community, there is complete denial that evolution exists.

The line of thought above leads us to an interesting comment on this. We know that, for instance, a fruit fly exists. Relative to us, it’s a fairly simple organism. It exists, so how did this come about? There are perhaps three alternatives. One is that fruit flies evolved from less complex organisms over the last 3 billion years or so. This is the view of modern biologists worldwide.

Another possibility is that a fruit fly spontaneously came into existence at some point in time, and it just reproduces. Since the genome of the fruit fly is now mapped, we know that it consists of 122.7 million base pairs, arranged along the DNA helix. The chance that this sequence could happen spontaneously is something like one in 10 to the power of 200 million. This number is beyond astronomical. The number of stars in the Milky Way is reckoned to be about 100 billion, a mere 10 to the 11th. The number of stars in the whole observable universe? About 100 billion times 100 billion, or 10 to about the power of 18. Again – an insignificant number relative to that fruit fly statistic. What does this mean? If the probability of a fruit fly self-creating in our solar system is small, what is the probability that it might come about somewhere else in the universe? Well, doing the elementary math … still about one in 10 to the power of 200 million.

O.K., there are simpler organisms, but the figure for E. coli is still 10 to the power of 8 million. So this is pretty unlikely too, to put it mildly. So the second alternative looks pretty unlikely, right? Is this an argument for some “intelligence” having pulled this off? Absolutely not! Because now that we know the mechanisms by which evolution works, it’s evident that the chance of these complex organisms evolving over the last 3 billion years is wonderfully high. We have even seen evolution in process in our lifetimes.

So what of the third option? That a superhuman being created the fly? But if this being – which we might call a higher power, or God, if we like – made the fly, would he do it in this unlikely way, rather than just letting it evolve? Probably not; as usual in scientific circles, the simplest answer is generally found to be most likely. Divine intervention theories are very unlikely to be correct, simply because we have no evidence of this kind of interference happening from outside, whereas we have mountains of evidence for evolution.

There is too little room here for all the details, but the conclusion that our lecturer came to was quite a thrilling revelation to me: that evolution is not something that happens once life exists – it is the definition of life. Life may be defined as matter that undergoes natural selection.

There remains a basic question that no one I know can yet answer satisfactorily: How did life get started? Once we know the answer to this, we will be able to figure out logically the probability of life beginning in other worlds. But we will still not know why the universe produced life at all. This, in my opinion, is where there ought to be no conflict between religion and science. One takes over where the other leaves off. I believe this is a healthy situation.

O.K. – far enough for now. But I will be watching for news from the front. As Patrick says, if we do find life on Mars, things will be looking a little more rosy for the theory that, given the right conditions, life always will evolve. My deepest instinct is that this is … doubtful. But I hope to enjoy being proved wrong!