Just Finished Reading: Rare Earth – Why Complex Life Is Uncommon in the Universe by Peter D Ward and Donald Brownlee (FP: 2000) [287pp] 

Humans have been wondering if we are ‘alone’ in the Universe for a long time – centuries at least if not longer. Only in the last 20 years or so, and mostly after the publication of this book, are we starting to get enough data together to start answering that question. The biggest impact on our understanding of the possibility of life elsewhere is the large and ever-growing number of planets already discovered with more coming in each day. With the launch and activation of the new James Webb telescope I imagine that these numbers will skyrocket. But not so fast, say the authors! Just because we’re finding planets doesn’t mean that we’ll find life and especially complex life. It’s really not that simple. For example, of the 8 (or 9 if you still count Pluto) planets in our system only 1 can definitely be shown to have complex life. If most star systems are like ours – which we suspect they’re not – then the odds are greatly reduced. Furthermore, as the authors point out, a good part of our galaxy might be life fee, or at least complex life free, because of the real danger of nearby stellar explosions and other cosmic threats. Not only do stars have habitable or ‘Goldilocks’ zones but so do galaxies. The authors even dismiss whole galaxies (of the ‘wrong’ type) likely to be unlikely candidates for life. So, are we alone? Is Earth a rare and precious example or are the authors being far too pessimistic? 

I knew going into this book that I’d have problems with the author’s conclusions. I am of the belief, and it is a belief, that life is common is our galaxy (I’m not going to discuss the universe as a whole because we’ll never explore the vast majority of it unless we can develop some very exotic propulsion systems). Surprisingly though, the authors agree that at least bacteria are indeed common throughout the cosmos. Although we presently only have a single example to work from – our home planet Earth – it appears certain that life emerged here almost as soon as it could and has been present ever since for around 3.7 to 4 billion years. Most of that time bacteria has been the only life present and it still makes up the vast majority of biomass on the planet. Bacteria is, and always has been a dominant lifeform. Reasonably extrapolating from our one example its probable that bacteria will exist on every world capable of supporting it. Where we disagree is what comes next. The authors argue (or just as often simply declare) that anything much more complex than bacteria has a much harder job of developing and thriving and, therefore, will be vanishingly rare. Generally, I found their arguments to support this conclusion (something that often felt already decided upon) varied between weak and disingenuous. Some had merit – the stability of various star types for example – but in every case they took doubts as fact and foibles as necessities – that planets with complex life demand large satellites, at least one Jupiter in the system to mop up potential planet killers and a whole host of other ‘reasons’ for Earth being close to unique. In each and every category their argument always managed to get the ‘benefit of the doubt’ even if that ‘doubt’ had to be manufactured in advance. Indeed, much was made of the fact that at publication date no Earth type planets had yet been discovered – despite the fact that the authors knew full well that technology of the time could not detect planets that small!  

I am of the opinion that, wherever conditions allow, life will emerge on planets throughout the galaxy. If time permits that life, certainly at the level of bacteria, will spread and become ‘endemic’ and almost impossible to remove with anything less than a truly planet shattering cataclysmic event. Once life is so established I think, in line with my reading of Stephen J Gould, it will inevitably increase in complexity for the simple reason that life at such a basic level will find it difficult to become less complex. Random mutations will, over time if conditions are reasonably stable, gradually and inevitably increase life’s complexity. Just how complex life will then become is anyone’s guess. Again, given enough time and reasonable levels of environmental stability, I see no reason why complexity cannot steadily increase. Will this produce intelligent life that we could converse with? Possibly. Again, we don’t know enough about how intelligence (what we have anyway!) emerged on the one planetary example we have. Intelligence and self-awareness might be a one in a million fluke, or it might be just a matter of time. We don’t know but I certainly don’t dismiss the possibility. Like the famous ‘Drake Equation’ the author’s produced an equation of their own. I’ve seen people plug in the most pessimistic figures into each function and the number they came up with is 10 – that 9 other human level civilisations in our galaxy right now. Personally, I think that number is way too low. Carl Sagan suggested that there could be 1000’s of civilisations out there, but I think that figure is probably too optimistic. Despite the fact that we haven’t been looking very long I think we might have stumbled upon at least 1 of them by now! I think the realistic figure is probably in the 100’s. Some will be less advanced than us (if that’s possible!) and others will be much more advanced. The galaxy is, however, on the large side so it’s entirely possible that our nearest intelligent neighbour might simply be too far away for us to notice each other. 

Looking within our own system we have, obviously, one strong example of complex life but are there any others close at hand? Personally, I wouldn’t be hugely surprised (though undoubtedly delighted) if we eventually find independently evolved bacteria in caves on Mars. The planet was wet for a while and it just might have been hospitable enough for long enough for life to emerge. As conditions worsened and life struggled to survive it would have moved underground. Complex, but still reasonably simple, life might be a possibility but bacteria are, I think, a distinct probability. If the suspected deep oceans of liquid water exist on some of Jupiter’s moons, then the odds of complex life there increase greatly. Again, personally I wouldn’t be in the least surprised if our first probes report fish happily swimming around in the pitch black beneath kilometers of ice. Overall, this book was pretty much what I expected so I wasn’t particularly disappointed that I disagreed with most of what the author’s proposed. It’s worth a read despite being 20 years out of date as well as being unduly pessimistic (trying vainly to retain *some* special place for humanity after so many demotions I think). Two more positive books on this subject to come later in the year. Reasonable.