The late great naturalist and writer Stephen Jay Gould, in his book Wonderful Life, once put forward a thought experiment that he called 'Replaying life's tape'. In this he stated that if you were somehow able to rewind the entire evolution of our planet to its start and press 'play', the likelihood of it leading to the evolution of life as we know it today is remote. Our very existence is based upon a million billion tiny chance events and advantageous mutations. Only one in every 1000 species survives and there have been several Mass Extinction Events (MEEs or sometimes called Extinction Level Events). Everyone knows that there was an MEE around 65 million years ago that polished off the dinosaurs and their cousins, but that was nothing compared to the Permian Era MEE that wiped out 95% of all species on the planet. And that was just one of several such events. So we're pretty lucky to be here.
Of course, whatever life had evolved during each 'replay' would still have had to follow the rules of Darwinian evolution, namely that:
- In a given environment, all organisms produce more offspring than can survive to then reproduce themselves.
- All organisms naturally vary.
- Offspring inherit characteristics from their parents and tend to be more like their parents than others.
- At least some of the variations in an organism lead to a greater number of its offspring surviving and reproducing relative to the offspring of others.
- This 'natural selection' means that these particular variations will become more prevalent in the population (as a consequence of the differential survival and laws of inheritance) as they are passed on to future generations.
Creatures adapt to their environments and are shaped by them. They are also shaped by their lifestyles and by sexual selection and there is often a fine balance between the two. Take the peacock's tail as an example; on the one hand, the bird has to be able to escape from predators, but on the other it needs to attract a mate. The peacock is a creature that is absolutely on the edge when it comes to balancing those two factors.
The creatures in these photographs look alien to us because the environment that they evolved to survive in is so alien; pitch black darkness, freezing temperatures, low oxygen, minimal food, crushing pressures ... it is like being on another world. But these creatures, bizarre as they are, have all evolved from the same primitive creatures that we did. They are all based upon carbon and use DNA. Aliens may be based on other elements and have an entirely different system of genetics. Even if the world they inhabit is Earth-like, what are the chances of evolution - with all of its chance mutations and billions of variations - arriving at anything that looks vaguely like an Earth species?
Suddenly the idea of little green men seems incredibly unlikely doesn't it?
The Deep: The Extraordinary Creatures of the Abyss by Claire Nouvian (ISBN: 978-0-226-59566-5)
And some great sea-life image sites worth visiting: