How often will sentience evolve on earth? From anthropology to the Fermi Pardox - via the Drake Equation

Hawks reviews research that suggests that "modern" evolutionary innovations are more likely to be repeatable (non-singular) than "ancient" innovations. He connects this to the Drake equation, the companion to the Fermi Paradox that attempts to estimate the prevalence of technological civilizations in our galaxy. He points out that since the only instance of sentience we know of is quite recent, it is likely that sentience is not a particularly singular innovation.

Personally, I'd bet we're not the first. Stephen Baxter wrote an immensely underappreciated science fiction novel (Evolution) that painted a rather persuasive picture of how sentience might come and go across the history of life on earth -- only once and briefly producing interplanetary technology (after this transiently spacefaring species passes, there's not much left for others to work from).

Hawks is inclined to think we're the first, but most likely not the last. Indeed, if we live out this century, I think it's likely we'll create other sentiences, both biological and otherwise. If we don't make it, the biological ones will still emerge some day, some place. Maybe they'll do a better job that us.

Back to the Drake Equation. The more we start to shift our estimates for the terms of the Drake Equation, the more the Omega term, L, looms larger (sorry). This term is often estimated based on the Fermi Paradox. Wikipedia (currently) has an excellent discussion of this relationship:

The remarkable thing about the Drake equation is that by plugging in apparently fairly plausible values for each of the parameters above, the resultant expectant value of N is generally often >> 1. This has provided considerable motivation for the SETI movement. However, this conflicts with the currently observed value of N = 1 — one observed civilization in the entire universe. Other assumptions give values of N that are <<>

This conflict is often called the Fermi paradox, after Enrico Fermi who first publicised the subject, and suggests that our understanding of what is a "conservative" value for some of the parameters may be overly optimistic or that some other factor is involved to suppress the development of intelligent space-faring life...

... L = the expected lifetime of such a civilization

Estimated by Drake as 10 years.

The value of L can be estimated from the lifetime of our current civilization from the advent of radio astronomy in 1938 (dated from Grote Reber's parabolic dish radio telescope) to the current date. In 2005, this gives an L of 67 years.

In an article in Scientific American, Michael Shermer estimated L as 420 years, based on compiling the durations of sixty historical civilizations. Using twenty-eight civilizations more recent than the Roman Empire he calculates a figure of 304 years for "modern" civilizations. Note, however, that the fall of most of these civilizations did not destroy their technology, and they were succeeded by later civilizations which carried on those technologies, so Shermer's estimates should be regarded as pessimistic.

The Wikipedia article estimates a low value for "safe" earth like planets, I read the most recent findings as much more encouraging but I'm far out of my expertise range.

If "safe" planets turn out not to be rare, then we're back to Drake's solution to the Fermi Paradox -- a 10 year lifespan for a technological civilization. My bet is that the small number is not so much L, as it is fc*L, so even if L is not short something happens to technological civilizations that causes them to lose interest in both physical exploration and communication with the likes of us. Something that produces a communicative sentience for no more than 10-40 years.