It's a great pity that most SF geeks and space nerds are far more interested in physics, chemistry, and engineering than in biology or evolution. The Fermi Paradox keeps popping up on the blogs I follow, and every time I shake my head at the colossal ignorance of people's assumptions about how likely it is for a life-bearing exoplanet to evolve sapience.
The Fermi paradox observes that there's a high probability of life beyond the Earth in the galaxy, and then asks, "why aren't we seeing any evidence of alien civilizations?" ( exoplanet digression )
If we ignore the vast number of unknown factors that might keep an earthlike world from acquiring a diverse and full ecosystem like our own, and just focus on the (probably) thousands of worlds that have evolved complex life forms, we get to the real issue that I wanted to talk about -- Fermi, and many other extremely intelligent and educated people, have all jumped straight over the evolution of sapience, taking it as an inevitable given, without really thinking about it properly.
Elephants mourn their dead. Humpback whales have incredibly complex songs that we are only now learning how to hear and analyze, and they exhibit altruism, thwarting the preying of their orca relatives against seals and other species.
Clearly elephants and whales are among the most intelligent species on the planet. Yet both have been decimated by human predation. They have been unable to act in a coordinated manner in response to our wholesale murder of their kind, either to flee and avoid us or to defend themselves. If sapience is something that just evolves gradually and inevitably over time, then we'd see more evidence of beings other than us that can organize and coordinate their behaviour, especially in response to threats.
Instead, there's a quantum leap in mentation between other smart creatures and us. And when we see a quantum leap in evolution, we are seeing the result of a genetic bottleneck, a period of (relatively) rapid change in response to dire selective pressure. 99% of species die out rather than make it past the bottleneck.
A definition, cribbed and grossly simplified from The Symbolic Species
by Terrence Deacon: sapience is the ability to think symbolically, to use abstract language (human language being a quantum leap towards greater complexity and versatility compared to all the animal languages we have studied). Everything else we label as human (tool making, tech, behavior, culture, society) grows out of the ability to think and communicate in an abstract, complex manner. Deacon's book makes a very persuasive case that a quantum jump in language and symbolic thinking came first.
Postponing consideration of Deacon's argument as to how and why our ancestors underwent a radical change in how they communicated, consider some alternative scenarios for evolutionary history on earth: ( smart whales, smart elephants, and smart pandas )
The speculative ETs in the Fermi Paradox are ETs that can either travel between the stars or send signals between the stars for us to hear. They can't just be smart, they have to be tool using, civilization-building creatures. They have to either possess a wanderlust that sends them into space and across interstellar distances, or a philosophical bent that causes them to want to speak to their fellow sapients elsewhere in the galaxy.
So from the thousands of worlds in this galaxy plausibly possessed of complex multicellular life, we have to narrow it down to however many worlds harbour life that made it through the quantum leap bottleneck to achieve sapience, and then narrow it again to however many of those sapient species happen to also benefit from being land dwellers, being possessed of dextrous paws or tentacles or whatever capable of making tools, and being possessed of a mindset that causes them to do something (say, build giant radio transmitters in orbit and start broadcasting a "we are here" signal to the cosmos) that could potentially be seen by us. Looking at the variety of creatures on earth, and how few of them are possessed of the ability to build tools even if they had the brains to do so, it seems safe to assume that less than one in a thousand sapient species in the cosmos are going to be civilized.
And how likely is it that the ones that are capable of civilization will be interested in the same philosophical questions as us, interested enough to make the effort to be noticed by the rest of the cosmos? So my answer to the Fermi Paradox is that even if sapience is a common evolutionary choice, it's entirely possible and even likely that we are either the only or one of the only civilizations in our own galaxy. No wonder we aren't finding any ETs out there.
Next time, hopefully soon, I'll talk more about The Symbolic Species
and how likely it was for us to get past that evolutionary bottleneck.