"Friar Broccoli" <EliasRK@gmail.com> wrote in message 
news:6aca6bc0-1c68-4916-ad98-32742cd69806@t54g2000hsg.googlegroups.com...

On Aug 13, 8:38 pm, John Harshman <jharshman.diespam...@pacbell.net>
wrote:

K_h wrote:

Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy.  On the other hand, 
intelligent
life should exist on a substantial fraction of planets with life 
because
natural selection broadly increases intelligence with time.

Does it? News to me. What evidence do you have that this is the case?

There has been an increase in the intelligence of a broad range of
species on earth with time.

Judging from the replies, it looks like there are a lot of people out there 
who really want extraterrestrial life to be relatively common.  The Fermi 
paradox, and the vast combinatorial possibilities for atoms and molecules, 
plausibly suggests that both extraterrestrial life and extraterrestrial 
intelligence are relatively rare.


The evolution of life and intelligence may occur in the following way.  The 
evolutionary tree of life may be like a shrub and the height of each shrub 
leaf, say, is proportional to the intelligence of the species represented by 
that leaf.  As the shrub grows, it has branches growing in all directions, 
from zero degrees to ninety degrees relative to the shrub's base.


A leaf at the end of a branch at zero degrees is almost at ground level and 
that leaf corresponds to a species whose intelligence has not changed much 
over billions of years, for example primitive bacteria like life.  Leafs at 
the top of the shrub, around ninety degrees, correspond to species with the 
most amount of intelligence (for the biosphere represented by that shrub).


Here on the Earth, for example, the hominoid family, and probably a few 
others species like Dolphins, are represented by leafs that are around 
ninety degrees on Earth's `shrub of life'.  As a shrub grows, it has 
branches that grow in all directions, from zero degrees to ninety degrees. 
In this sense evolution is not selecting for intelligence since the branches 
are randomly growing in all directions.


But there is a broad increase in intelligence since the average height of 
the shrub increases while it grows.  On any biosphere, as its `shrub of 
life' grows there will probably come a time when a leaf or two reaches a 
sufficient height that its corresponding species is capable of radio 
astronomy.  Once this happens then that species reworks that planet's biota 
which prevents any other species from evolving into high intelligence.  It 
is certainly possible that most planets with life follow this pattern.


There is no evidence that other instances of the origin of life, with a 
different genetic basis, would be consumed by any other life prior to 
establishing its own survival.  A genetic code based on a different set of 
atoms and molecules would not necessarily be palatable to any other life. 
In fact, it could be toxic.  Two different sets of biochemistry could have 
their progeny ignore each other like many species on Earth only have a very 
small set of predator and prey.  Obviously they would co-evolve because of 
mutual interactions and symbiotic relationships would exist.


If multiple instances of the origin of life occur the same planet then there 
is no reason to think that they would not all have long-term progeny.  Drop 
the old western mentality that says "This planet is not big enough for the 
both of us".


There is no evidence that (1) DNA is the only basis for life, (2) multiple 
instances of the origin of life have occurred on the Earth, (3) on any 
planet one origin of life make other such origins implausible, and (4) 
primitive self-replicating molecules are forming all the time on Earth.  In 
fact, there may never have been an origin of life in the solar system.  Life 
may have migrated to the solar system on debris from an earlier solar system 
and this could explain Earthly life so soon after the Earth's formation.


Since little is known about the geology and chemistry of planets in other 
solar systems, there could be many ways that an oxygen rich atmosphere 
arises by non-biological means.  Check out the below link for just such an 
example.  To claim that oxygen in a planet's atmosphere is a litmus test for 
life is unfairly stacking the deck against more prosaic possibilities.  It 
is unlikely that alien life would use the exact same photosynthesis that 
biological processes employ on Earth, or even have O2 as a waste product.


http://www.physlink.com/News/020304ExopanetOC.cfm


With just today's technology, astronomers are able to map about a million 
galaxies in the Sloan digital sky survey.  So it is fair to assume that a 
civilization in our galaxy, that is 200,000 years ahead of ours, would have 
mapped all, or most, of the stars and planets within the Milky Way galaxy. 
To see why note that, in the past century, the technology was developed to 
automate the production of hundreds of millions of cars.  A civilization 
200,000 years ahead of ours would easily have automated the production of 
millions of large space based telescopes capable of discovering most of the 
planets within the Milky Way.


Such a civilization would already know about the Earth and would be capable 
of sending space probes to Earth.  Furthermore, a civilization like that 
could easily automate the long term continuous broadcasting of 
multi-frequency signals toward millions of favorable planets, especially 
since its space based automatic broadcasting equipment would have automated 
self maintenance systems and therefore require little or no effort to 
maintain.  Fermi's paradox applies not only to extraterrestrial life 
visiting the Earth but also to extraterrestrial life broadcasting to the 
Earth.


In conclusion, it is quite possible that f_L is a very small number and life 
is quite rare.



k