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View Full Version : How many planets with bacteria, according to Alan Bond?



Tom Mazanec
2013-Jan-05, 07:50 PM
On the improbability of intelligent extraterrestrials (1982) by Alan Bond estimates that, IIRC, 1 in 50,000 galaxies like the Milky Way have a planet with life of the complexity of Homo sapiens. I cannot find a copy of this, but I wonder...does he give an estimate for the frequency of planets with life as complex as bacteria?

Colin Robinson
2013-Jan-06, 02:54 AM
On the improbability of intelligent extraterrestrials (1982) by Alan Bond estimates that, IIRC, 1 in 50,000 galaxies like the Milky Way have a planet with life of the complexity of Homo sapiens. I cannot find a copy of this, but I wonder...does he give an estimate for the frequency of planets with life as complex as bacteria?

I don't know, but in any case if you're looking at estimates made in 1982, you'd need to keep in mind basically nothing was known then about how common exo-planets are, or the range of orbits and sizes...

Tom Mazanec
2013-Jan-07, 01:34 PM
From what little I know of it, the estimate was based on a mathematical probability of complexity, and was actually optimistic for the time about planet formation.

TooMany
2013-Jan-08, 05:36 PM
When a process is driven by evolution, complexity naturally follows as adaptations are generated. It is a matter of opportunity combined with sufficient time. In our case 3.5 billion years. I don't think that an estimate based on probability and complexity of organisms is meaningful because evolution just makes complexity. The question is how fast does the complexity increase. We can probably get some idea from studying life on earth.

theloniusmonkey
2013-Feb-26, 08:56 PM
On the improbability of intelligent extraterrestrials (1982) by Alan Bond estimates that, IIRC, 1 in 50,000 galaxies like the Milky Way have a planet with life of the complexity of Homo sapiens. I cannot find a copy of this, but I wonder...does he give an estimate for the frequency of planets with life as complex as bacteria?


Love to see where he came up with these numbers. It seems utterly ridiculous, beyond conjectural.

Noclevername
2013-Feb-27, 01:23 AM
When a process is driven by evolution, complexity naturally follows as adaptations are generated. It is a matter of opportunity combined with sufficient time. In our case 3.5 billion years. I don't think that an estimate based on probability and complexity of organisms is meaningful because evolution just makes complexity. The question is how fast does the complexity increase. We can probably get some idea from studying life on earth.

Evolution can lead to simpler structures, if that's what survives better. Biologically expensive traits are lost such as cave-fish eyes.

Solfe
2013-Feb-27, 12:24 PM
1 in 50,000 galaxies? That is a massive number planets that don't have human-like life. I am not saying its wrong, but as other have said, there have been great advances in discoveries of planets. I suspect that there are a far more planets than Alan Bond believed in the eighties.

Obviously, a great many of planets (perhaps all but a handful) discovered don't look especially habitable for viruses/microbes let alone, human-like creatures. It would be more interesting to see a number of planets vs. life rather than number galaxies vs. life.

TooMany
2013-Feb-27, 07:42 PM
Evolution can lead to simpler structures, if that's what survives better. Biologically expensive traits are lost such as cave-fish eyes.

Well, you can call that a simplification if you like. If an organ no longer serves a useful purpose, there is no evolutionary pressure to maintain the organ as it was. Thus through natural variation, the genes that code the organ gradually fail to make the organ as it was anymore. It's really that same thing happening as when things are added, except there is no benefit so decay through variation sets in. As you say it may be beneficial if less energy is devoted to the organ, so variations that reduce consumption by the organ are selected.

While whales lost their feet, at the same time they modified and added other things to adapt to their new environment. Vestigial feet still show up in some whales.

Do such changes imply an overall simplification of the organism? I don't know whether the size of the genome of some organisms actually shrinks. However, I'll stick by the general statement, that overall, evolution moves toward greater complexity. If it were not so, we wouldn't be here typing.

JCoyote
2013-Feb-28, 12:33 AM
However, I'll stick by the general statement, that overall, evolution moves toward greater complexity.

I'm not so sure about that; overall do we see more complexity in the world than existed in the ages of dinosaurs? It would be nice if we had a full sequenced 65 million year old genome. Is there a maximum useful capacity of genetic/protein information? Lets imagine there is a practical limit to the size of a genome for a moment... in which case, the largest practical genomes could have been reached a very long time ago, and ever since has been a competitive rearranging of similar complexity.

John Mendenhall
2013-Feb-28, 12:50 AM
Evolution can lead to simpler structures, if that's what survives better. Biologically expensive traits are lost such as cave-fish eyes.

Agreed. Evolution is the ultimate empiricist. If it works, it stays.

TooMany
2013-Feb-28, 01:06 AM
I'm not so sure about that; overall do we see more complexity in the world than existed in the ages of dinosaurs? It would be nice if we had a full sequenced 65 million year old genome. Is there a maximum useful capacity of genetic/protein information? Lets imagine there is a practical limit to the size of a genome for a moment... in which case, the largest practical genomes could have been reached a very long time ago, and ever since has been a competitive rearranging of similar complexity.

I think you will have a difficult time proving that evolution does not increase complexity. All you have to do is look at the fossil record. Animals started out very simple and got more and more complicated. OTOH onions have far more DNA than humans. So apparently the amount of genetic material is not a good indicator of structural complexity. If there is some limit in genome size, humans have not reached it.

Some organisms seem to have been stable over vast periods of time, like alligators. But on the whole, there has been development. Would you argue that dinosaurs have the same complexity as humans? This is certainly not true when it comes to the nervous system. I'm not sure about other organs, we really don't know. But why would only the nervous system become more refined?

galacsi
2013-Feb-28, 11:00 AM
I'm not so sure about that; overall do we see more complexity in the world than existed in the ages of dinosaurs? It would be nice if we had a full sequenced 65 million year old genome. Is there a maximum useful capacity of genetic/protein information? Lets imagine there is a practical limit to the size of a genome for a moment... in which case, the largest practical genomes could have been reached a very long time ago, and ever since has been a competitive rearranging of similar complexity.

I am not sure too , but if life on Earth is 3,500 millions years old , between us and the dinosaurs , a little less than 2% of this duration has elapsed. So this is not surprising if there no striking difference in complexity.

MaDeR
2013-Feb-28, 11:59 AM
However, I'll stick by the general statement, that overall, evolution moves toward greater complexity. If it were not so, we wouldn't be here typing.
Nope. While evolution CAN result in greater complexity, it is not tendency, trend nor goal. Evolution is blind force, it does not have goals. Complexity will happen if it is beneficial - and it is not always beneficial. In fact, most successful organisms in hsitory of Earth are one-celled life.

Viruses would not exist if evolution only moved towards great complexity.

Noclevername
2013-Feb-28, 12:43 PM
Well, you can call that a simplification if you like. If an organ no longer serves a useful purpose, there is no evolutionary pressure to maintain the organ as it was. Thus through natural variation, the genes that code the organ gradually fail to make the organ as it was anymore. It's really that same thing happening as when things are added, except there is no benefit so decay through variation sets in. As you say it may be beneficial if less energy is devoted to the organ, so variations that reduce consumption by the organ are selected.

While whales lost their feet, at the same time they modified and added other things to adapt to their new environment. Vestigial feet still show up in some whales.

Do such changes imply an overall simplification of the organism? I don't know whether the size of the genome of some organisms actually shrinks. However, I'll stick by the general statement, that overall, evolution moves toward greater complexity. If it were not so, we wouldn't be here typing.

Evolution moves in any direction that works. It spreads out every which way. Sometimes that leads to complexity, yes. Sometimes it doesn't. So the complexity that produced us isn't an overall trend so much as it is the high end of a probability distribution.

TooMany
2013-Mar-01, 10:33 PM
Evolution moves in any direction that works. It spreads out every which way. Sometimes that leads to complexity, yes. Sometimes it doesn't. So the complexity that produced us isn't an overall trend so much as it is the high end of a probability distribution.

In spite of the evidence that we have, you seem to hold that complexity is just a "sometimes" thing.

Evolution is about survival and reproduction. It is driven by adaptation to the environment, including competition with other life forms. This causes life forms to become more complex, rather like an arms race.

All animals are predators, if not on other animals, then on plants. In becoming more effective predators, animals gained eyes, ears, teeth, claws, limbs, wings and elaborate nervous systems. A recent increase in nervous system complexity has had profound effects. The nervous system developed so much that it can now "imagine" things and then implement these imaginings, if they appeared fruitful.

The conjecture that evolution of life in a suitable environment (like earth) would stagnate in most cases (staying at a bacterial level) appears to be contradicted by our single example of life (on the earth). I doubt that there is anything unusual about evolution of life (on Earth in particular) that led to higher life forms, beyond a suitable environment.

There are those who claim that human-like intelligence is an extremely unlikely outcome of evolution. This ignores the fact that the advantages of complex nervous systems are huge. While it may take a long time for the necessary structures to evolve, given enough time, it will happen because it has unparalleled survival value.