Somewhere between 1.75 billion and 3.25 billion years from now, Earth will travel out of the solar system’s habitable zone and into the “hot zone,” new research indicates. … In the habitable zone [HZ], a planet (whether in this solar system or an alien one) is just the right distance from its star to have liquid water. Closer to the sun, in the “hot zone,” the Earth’s oceans would evaporate. (
Do you have a citation for sexual reproduction having evolved more than once?
I thought these hard steps were toward getting intelligent life. So what does it mean to have hard steps in our future? Also I'm not sure what evolution versus random search has to do with this--maybe it's being implied intelligence/Cambrian explosion is a single step. While I see how having one or two hard steps leads to the origin of life being not likely a hard step, I don't see why the spacing of 0.6 billion years between the Cambrian explosion and humans says anything about intelligence being a hard step since it might be that intelligence was hard and the explosion was not. If anyone understands this, maybe they can explain.
I can't see the full article, but what I wanted to know is do you still deem multi-cellular life a plausible (or the only plausible) hard step?This paper http://www-eve.ucdavis.edu/...cites multiple sources for the argument that m-c life independently originated over and over again. Does this count as evidence against that view?
A classic cite is: Harry J. Jerison (1991) Brain Size and the Evolution of Mind, American Museum of Natural History, New York.
Asexual procreation in animals is usually a short term survival mechanism: their populations will always go extinct if asexual reproduction is maintained for longer periods. Sex is needed for them, as it is for us, to increase the genetic diversity of new generations, it offsets the slow reproductive cycles of animals and our lack of horizontal gene transfer.
Even if brain and bodies sizes haven't been monotonically increasing, there have been consistent trends.
Honestly I don't know. Do you have any reference.
Even if sex isn't needed for multi-cell bodies, it might be needed for the kinds of bodies that can make intelligence.
Possibly, but that doesn't seem intuitively obvious.
There are several species of parthenogenic lizards that reproduce asexually. Since we evolved from lizards it would seem plausible that in an alternate world we could have evolved from these type of lizards.
It could be pointed out that these lizards descend from sexual ancestors, and they are not completely asexual, since they can mate and produce viable offspring with males of closely related species, therefore perhaps sexual reproduction might be needed to evolve an animal with the complexity of a lizard, but AFAIK there is no compelling evidence to support that position.
I looked at it, but I didn't find the explanation very conceptual. I think you're a better writer today than you were then.
I think I'd put it (very roughly) this way. If the time window is smaller than the average time for the first event, with additional required events the observed times for later events become indistinguishable.
Then, while it's true that our best estimates of the later events will be that they're of equal (additional) duration, the reason is that we lack information to distinguish them.
This says that the greater error involved in the respective inferences is what grounds warrant for belief that the intervals are equal. We are "confident" (then, a misnomer) that the intervals are equal based on the absence of information to distinguish them.
But (unless it's systematic absence, which is itself information), it isn't possible to ground knowledge in information's absence.
You can't be bothered to follow the link?
Even so, I showed fifteen years ago that that if all these steps were hard, i.e., if on a random planet each step would usually take longer than the time window for life on the planet, then given that intelligence eventually appears before the window closes, then the actual distribution of durations observed between the steps (and the duration between the last step and the end of the life window) would be roughly equal. (To be precise, drawn from the same distribution with a modest variance.)
It would help to have a conceptual summary of this argument.
Sounds plausible, thanks.
For the purpose of estimating the time distribution of events that lead to intelligence, what matters is how long is the window is open for simple life that can't restructure everything. Yes of course, once advanced life appears everything can change.
The post I linked to about eukaryotic life described it as the key to getting multi-cellular life.
1) Robin, unless you consider the likelihood of intelligence surviving long term to be negligible, any estimate of earth's future habitability which doesn't factor in the desires of intelligent creatures seems irrelevant.2) That said, if you *were* to revise your future-earth-habitability model to include the effects of intelligent activity, this would appear to leave you in the position of believing that the likelihood of our descendants deciding to (e.g.) move Earth to a higher orbit before it fries affects, among other things, the relative likelihood of terrestrial life having arisen via in-place evolution vs.panspermia. Which seems a fairly non-intuitive connection to be making. Can you or someone else help me clarify my thinking here?
VV is right: it is hard to detect Earth-sized planets (or any rocky planets for that matter), so the fact that we mainly detect gas giants is biased, it's even harder to detect life on those planets (although a civilization would make it easy for us) and it's currently impossible to detect Earth-sized moons around exo-gas giants. It may be that life isn't very rare IF you have the right planet: a rocky planet in the habitable zone, preferably with a large moon or itself a moon.
In 2010 you said:
It seems to me that if the great filter is to consist of just one big step, the only plausible possibility is the development of multi-cellular life. All the steps before that one seem able to spread to other star systems via single-celled life hidden in dust, and it seems we haven’t had a big filter step since the multi-cellular innovation.http://www.overcomingbias.c...
How exactly do you square this with
> The best candidates for a hard step in the history of life on Earth seems to be the origin of Eukaryotes.
Is there evidence for eukaryotic panspermia?
Even if brain and bodies sizes haven't been monotonically increasing, there have been consistent trends. Even if sex isn't needed for multi-cell bodies, it might be needed for the kinds of bodies that can make intelligence.