Life in the Universe part 5: How many planets will evolve intelligent life?

This is part of the Life in the Universe series of posts. Go here for the first one.

Part 4 talked about the probability of life in some form obtaining a foothold on any given suitable planet. This post will look at how likely it is that any of these possible examples of life will stick around long enough to develop intelligence.

What is intelligence?
A 1994 report by a large group of researchers, called Mainstream Science on Intelligence devised a definition for intelligence that was summarised as "a broader and deeper capability for comprehending our surroundings — “catching on”, “making sense” of things, or “figuring out” what to do," although many other, similar possibilities have been put forward.

Basically, 'intelligence' seems to indicate a life-form's built-in capability and conscious desire for changing its surroundings, actions and thoughts in order to solve problems presented by the demands of being alive.

How long does intelligence take to evolve?
As with other posts in this series, we only have one example upon which to base our discussion: Us*. On our own planet, although simple forms of life evolved fairly soon (in the grand scheme of things) after conditions became habitable, intelligence by any definition didn't come about for a few billion years. Assuming that our circumstances are typical with regards to the development of intelligent life**, we may expect that life needs a long time to get clever.

So how many planets will evolve intelligent life?
The crux of the matter is this: intelligence needs time to evolve. If intelligence needs time, then life needs a stable environment in which to grow for a significant portion of the lifetime of a suitable star. Stability comes from a number of factors, many of which have been discussed in previous posts in this series regarding what makes suitable stars and planets: stable orbits, stable stars and the like. Other things that haven't been discussed so far include the local neighbourhood:
  • On Earth, out in the backwaters of one of the galaxy's spiral arms, we don't encounter too many other stars. If we were closer in, we'd have a greater chance of relatively close approaches with other stars. Most of these would be too far out for us to notice directly, but they could stir things up in the Oort cloud and send potentially deadly objects towards the inner solar system.
  • Our solar system's biggest and baddest family member, Jupiter, acts a little like a cosmic vacuum cleaner, protecting us from some of the celestial ice bergs that may otherwise float our way (although see this post for more in-depth comments!)
  • Our moon*** has had a stabilising effect on Earth's rotation, and has also possibly shielded Earth from potentially life-ending impacts.
Given the variability of the above and our lack of information on the subject, it's almost impossible to predict a value for how many life-suitable planets will go on to nurture intelligence. That doesn't mean it doesn't make an interesting discussion point, though...

And, just as a treat and not entirely relevant to this post, here's the opening sequence from the 2005 film adaptation of the Hitchhikers' Guide to the Galaxy, the song So Long and Thanks for all the Fish, written by Garth Jennings

Life in the Universe
This is the fifth in a series of posts about Life in the Universe, culminating in a discussion about the Drake Equation. The first post concentrated on the number of suitable stars formed each year. The next one will follow on from this one and discuss how often intelligent life will develop the means and desire to communicate with other intelligent life.

* Of course, it can be argued that there are other intelligent species on Earth at the moment. One example is the dolphins, known to be particularly intelligent members of the animal kingdom. I cannot help but include a quote from the Hitchhikers' Guide to the Galaxy here: "... man had always assumed that he was more intelligent than dolphins because he had achieved so much - the wheel, New York, wars and so on - whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man - for precisely the same reasons."
** Although we don't really have much in the way of evidence to make an assumption either way.
*** Imaginatively named "The Moon".


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