In the process, I took pains to explain how unusual humanity is and that we may even be unique in the universe. The reasons for this are complex, but worth consideration.
We all know that, without the demise of the dinosaurs about 65 million years ago, mammals could not have emerged as the dominant class and we would not exist. The dinosaurs had ruled the planet for about 165 million years, with no sign of dying out. Without the cosmic collision that destroyed them and much else, they would still rule the Earth.
The subsequent evolution of various hominins was also not guaranteed. It only occurred because of propitious circumstances, which was also why our particular species evolved to become dominant. But this was not guaranteed. The explosion of the super volcano Toba in Sumatra about 70,000 years ago wiped out many species, with a few of our kind surviving due to their intelligence and survival skills. That event may also have been the trigger to start a migration northwards that led to us living all over the world.
Some would claim that we evolved our large brains and ability to speak after a long period developing in water (the Aquatic Ape Theory). If so, that would have been ususual and lucky.
Life on this planet was also lucky. Not only is the solar system in a relatively quiet part of the outskirts of the Galaxy, shielding it from the violence evident nearer the centre, no nearby supernova (exploding star) has sterilised the system. Our sun is well-behaved star with still some 5 billion years of life and Earth is located in a zone where the temperature is not too extreme (Venus is too close and Mars too far for the evolution and sustenance of life). It is also now recognised that without our unusually large Moon, itself the result of a chance collision between the proto-Earth and another large planetismal (Thea), life may not have been able to develop. This is because the Moon stabilises Earth’s rotation and creates tides in the oceans. Without tides, life in the sea might not have been able to move onto the land. Much of this is explained in something called ‘The Rare Earth Hypothesis’; namely that a system like ours is rare in the universe.
One scientist has drawn attention to fact that, for the past 7000 years, sea level has been remarkably and unusually stable. He claimed that this may have contributed to the development of civilization. The reason for this is that all the major civilizations developed on coasts, especially on river deltas. Repeated changes in sea level could have inhibited the development of civilization. We have also built our civilization during an interglacial period; we could not have done so with ice sheets covering most of Europe.
At the end of my essay, I wrote:
Does it not seem that we have been lucky? Or rather that we owe our existence to a series of fortuitous chance events, events that must be rare in themselves, never mind in combination? If that is true, then we are probably a very rare phenomenon, an intelligent species that has developed advanced technology, even now venturing into space. My guess is that the chance of another such species emerging elsewhere in our Galaxy is almost nil and we may indeed be alone.
In short, we have won the lottery of life. But let us look at this another way. Modern cosmologists believe that the universe we inhabit, only part of which we can see, is infinite! (That statement deserves its exclamation mark.)
Now in an infinite universe, anything that is physically possible must happen. Moreover it must occur an infinite number of times. From that perspective, our emergence is no surprise. In every lottery there is always a winner. No matter how lucky it seems that we have been, in an infinite universe, something like us was bound to emerge. That also probably means that the universe contains an infinite number of Earths, all with slightly different histories! (Another exclamation mark is justified.)
Some have pointed out that life has only been able to develop because the fundamental physical constants of our universe seem fine-tuned to permit it. Slightly different settings of these constants would not have allowed stars, or galaxies, or life to emerge. This seems lucky and some think it is evidence of a designer (The Anthropic Principle). But there is a simpler explanation.
Cosmologists now believe that many universes emerge from an eternal multiverse existing in many dimensions and that each of these universes has its fundamental constants set at the time of emergence. Multiple universes popping out of a timeless multiverse with different constants must mean that sometime (time is meaningless here) some will emerge that have the constants propitious for life. That is why we are here. We are here because it is possible and inevitable.
But that does not mean that we will always be here. Financial advisers always warn that ‘past performance is not a guide to future performance’. Likewise, although we have been lucky so far, we might not always be so. We have escaped global thermonuclear war, but only just, and many natural disasters could obliterate our civilisation. Even now, we seem bent on destroying our civilisation by allowing greenhouse gases to proliferate. Uncontrolled global warming has many serious consequences, the worst being the rise in sea level that will inundate major coastal cities. To survive, we will need to take control of the planet, but have we the will to do this?
One can sum all this up with the words of a song from the First World War (‘We’re here because we’re here’), which expresses both the resignation and bewilderment of those who find themselves, as we do, in a situation that almost defies explanation.