Re:The future lifespan of Earth’s oxygenated atmosphere
by istjohn on Wednesday March 03, 2021 @09:39AM
(#26328863)
Why do we think the origin of intelligent life requires a few hard steps and not just a continuous progression or perhaps one hard step and otherwise a steady progression?
Re:The future lifespan of Earth’s oxygenated atmosphere
by derekp7 on Wednesday March 03, 2021 @09:59AM
(#26329169)
I think the hard steps are sharp divisions that had a long time in the status quo, then a sudden random development. Single-cell to multi-cellular. Development of nerve tissue that can collect information, make decisions, and influence the organism. Centralization of a bundle of nerves into a decision making center. Then you get to higher order steps that probably aren't as complicated, such as communications and organization, then all the steps that humans went through that took a while, without having major biological changes that enabled them.
Re:The future lifespan of Earth’s oxygenated atmosphere
by DavidSJ on Wednesday March 03, 2021 @03:42PM
(#26334168)
I think any step which occurred independently on multiple occasions is probably not a hard step. The origin of multicellular life from unicellular life occurred on at least three separate occasions independently.
However, I think at the very least that the origin of the first cells, as well as perhaps the transition from Archaean/Prokaryotic cells to our symbiotic Eukaryotic ancestor may qualify.
If that hypothesis holds, then conditional on all the steps having completed on a given planet, they will have done so roughly equally spaced in the time allotted, regardless of their relative difficulty.
So, for example, if the window on Earth is 5 billion years, and there are four hard steps to complete, then, conditional on all four steps finishing, we expect each step to have taken about 1 billion years, give or take, with about 1 billion years left to go.
(See the Technical Appendix to Robin Hanson's Great Filter essay: http://mason.gmu.edu/~rhanson/greatfilter.html#appendix, or his more detailed discussion of this particular point: http://mason.gmu.edu/~rhanson/HARDSTEP.PS)