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Comment by PixelRobot | Hacker News Reader

That's some optimistic data there.

These are the values originally used by Drake et. al. when they proposed the equation in 1961. Many were outright guesses. Nevertheless, 50 years later, we still don't have much better guesses, but this may change soon for proportion of planets with stars (is probably higher) and stars with earthlikes (coming soon).

That's what I thought - "average number of Earth‐like planets per star with planets: 2"... really?

I'd like to know where that value comes from, is there any scientific basis to it?

It seems to be just speculation. There's not much data you can use to guess those numbers with the current scientific knowledge.

When the equation was first proposed, I'd guess they assumed Sol is an "average" solar system, and given that we have Earth, which is by definition Earth-like, and Mars, Venus, and several of the Jovian moons, which could all fit a suitably loose definition of "earth-like", Drake might even have thought he was being conservative.

That raises the question: What's the least-optimistic combination of data that yields at least one communicating civilization?

Just change "fraction of Earth‐like planets that develop life:" from 1.0 to 0.1 and you get 1

That guess could be off by many orders of magnitude as we have exactly one data point right now

More interesting to me is the chance of intelligent life variable. A couple of months ago on Ars Technica iirc, there was published a writeup on a paper on how macro life (much less intelligent life) requires something analogous to mitochondria for the cell to be large enough to handle that level of complexity (the problem being caused by the geometric relationship between volume and surface area). the paper goes on to say that the chances of one organism entering another and them then entering a mutually beneficial symbiotic relationship as being astronomically low (it is, however, a function of time, but Ars implied (iirc) that this doesn't noticably help the Drake equation the chance is that low). Based on this I would adjust Fi by a couple dozen orders of magnitude

Oh, the chances of such symbioses aren't too bad. They happened many times.

See Mitochondria, Chloroplasts, perhaps Cell nuclei, the retro virus that's incorporated in our genes that make mothers' immune system not reject the fetus. (See https://secure.wikimedia.org/wikipedia/en/wiki/Endosymbiosis and https://secure.wikimedia.org/wikipedia/en/wiki/Endosymbiotic... for more.)

On a scale broader than single cells there are around 80% of vascular plants and their symbiosis with fungi, the bacteria in our guts, the worms close to black smokers, certain sea cucumbers that absorb algae and live off their photosynthesis, and much more.

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