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The term ''race'' here means a species of sentient individuals (not an ethnographic subdivision of a single species); for example, humans all belong to only one race, the human race.

The term ''race'' here means a species of sentient individuals (not an ethnographic subdivision of a single species); for example, humans all belong to only one race, the human race.

==Scientific terminology applied to evolution==

== Extraterrestrial life as a scientific hypothesis ==

The terms fact and theory can be applied to evolution, just as they are to gravity.<ref name=Moran/> Misuse and misunderstanding of how those terms are applied to evolution have been used to construct arguments disputing the validity of evolution.

Vigorous scientific research on the subject is fairly limited, and has focused on both the "micro" and "macro" aspects of the problem:

In the study of biological species, the facts include fossils and measurements of these fossils. The location of a fossil is an example of a

# The [[exogenesis]], nature, survival, and movement of primitive life forms, including the hazard that such microbes might pose to [[astronaut]]s or to the earth itself.

fact (using the scientific meaning of the word fact). In species that rapidly reproduce, for example  [[fruit flies]], the process of evolutionary change has been observed in the laboratory.<ref>{{cite journal |author=Dobzhansky T, Pavlovsky O |title=Experimentally created incipient species of Drosophila |journal=Nature |volume=230 |issue=5292 |pages=289–92 |year=1971 |pmid=5549403 |doi=10.1038/230289a0}}</ref> The observation of fruit fly populations changing character is also an example of a fact, using the scientific meaning of the word fact. So evolution is a fact, at least using the scientific meaning of the word fact. These facts require an explanation, just as the observations of gravity did.

# The possibility of prior or future detection, contact, trade, or war with an extraterrestrial [[civilization]].

In biology, there have been many attempts to explain these observations over the years. [[Lamarckism]], [[Transmutationism]] and [[Orthogenesis]] were all non-Darwinian theories that attempted to explain the observations of species and fossils and other evidence. However, the '''Theory of Evolution''' is the explanation for all relevant observations regarding the development of life, based on a model that explains all the available data and observations. Thus, evolution is not only a fact but also a theory, just as gravity is both a fact and a theory.

=== Microbes and other primitive forms ===

[[Image:PIA09027 a anno br.jpg|400px|right]]

|-  

 

!style="background:#d0e5f5;color:black" |Gravity!!style="background:#d0e5f5;color:black" |Evolution

# Could a microbe of extraterrestrial origin somehow come to earth and cause a killer [[pandemic]]?<ref>This question of ''back-contamination'' was a serious worry in the middle years of [[Project Apollo]]--that is, the time of the first four missions of that project. [[National Aeronautics and Space Administration|NASA]], the launch authority for Apollo, required the crews of the first three missions actually to reach the [[moon]] to spend weeks in [[quarantine]] while under the constant care and watch of a [[physician]]. Only after three crews landed on the moon and returned to earth with no ill effect and no evidence of having contracted any communicable disease on the moon or in space did NASA drop that requirement. (The crew of [[Apollo 13]] did not face this requirement because their in-flight emergency precluded their planned landing.)</ref>

|-

# Did life on earth begin with the "seeding" of the earth from outside? This theory, called [[panspermia]], alleges that either (a) the earth acquired the seeds of life by passing through the tail of a [[comet]], or (b) an extraterrestrial ''civilization'' sent the seeds of life ''deliberately'' for one reason or another. Extraterrestrial microbes would be involved in either case.

|Things falling is an observation of the pull of bodies towards each other.||Fruit flies changing generation to generation is an observation of generational organism change.  

# Might a human crew or human-directed robotic explorer find extraterrestrial microbes on another [[planet]]?

|-

 

|Bodies pulling towards each other is called gravity.||Organisms changing generation to generation is called evolution.  

With the continued development and perfection of telescopes, [[Astronomy|astronomers]] and [[rocket]] [[science|scientists]] have openly and often feverishly speculated about whether the other planets in our [[solar system]] might harbor forms of life that originated on those planets. This speculation has also extended to [[Titan]], the largest satellite of the planet [[Saturn]].

 

|Gravity is a fact.||Evolution is a fact.

The major considerations driving such speculation are the requirements of life, and the difficulty with the theory of [[abiogenesis]] as a workable origin of [[life]] on [[earth]]. Most scientists engaged in such speculation seem to agree that life requires at least two things in order to self-generate in any environment:

 

!style="background:#d0e5f5;color:black" |An explanation for the facts of gravity.!!style="background:#d0e5f5;color:black" |An explanation for the facts of evolution.

|[[Aristotle]] and [[Galileo]] created explanations of the ''fact'' of gravity. These are now obsolete explanations. ||[[Lamarckism]], [[Transmutationism]] and [[Orthogenesis]] were created as explanations of the fact of evolution. These are now discredited explanations.  

[[Image:Mars_meteorite.jpg|thumb|150px|[[Meteor]]ite believed to have once been a part of [[Mars]] and to contain [[fossil]] evidence that primitive [[life]] may have existed on Mars.[http://spaceflight.nasa.gov/gallery/images/mars/meteorites/html/s94_032549.html Image source] ]]

Currently the most exciting subject for speculation concerning extraterrestrial life is the planet [[Mars]]. Its atmosphere is quite thin, and this would militate against the presence of life or, more to the point, the presence of standing or flowing water. But photographs taken from orbit and from the surface of Mars reveal erosion channels that strongly suggest that water once flowed on Mars. Indeed, the first graphic above shows changes in a gully in two views of it, taken four years apart--as if liquid water had opened another erosion channel in the meantime. (The operators of the Mars Global Surveyor insist that such pictures might still contain artifacts that make them unsuitable for scientific research, and hence disclaim any definite conclusion that anyone might be tempted to draw from them.) The second graphic shows a [[meteor]]ite, found in [[Antarctica]] in 1984, containing microscopic cavities that once might have held [[microbes]] and that, until recently, was believed to have fallen to earth from Mars.<ref>Donald L. Savage, James Hartsfield, and David Salisbury, "[http://www2.jpl.nasa.gov/snc/nasa1.html Meteorite Yields Evidence of Primitive Life on Early Mars]," ''Mars Meteorite Project'', press release 96-160, August 7, 1996. Retrieved April 17, 2007, from the [[Jet Propulsion Laboratory]] Web servers.</ref>

|[[Isaac Newton|Newton's]] explanation of gravity is approximately correct but required refinement.||[[Charles Darwin|Darwin's]] explanation of evolution is approximately correct, but required refinement.

 

If one could show that abiogenesis occurred on Mars, then that process was far more likely to have occurred on earth than it would be absent such a showing or finding. Yet apart from the reliability of such evidence is this one inherent weakness for this argument: it assumes that life ''found'' on Mars ''originated'' on Mars. The [[Hydroplate theory]] of the [[Great Flood]] suggests that large quantities of water, including muddy slurries, were ejected into space during the initial fissure of the original earth's crust, and that these ejecta persist today as [[comet]]s, [[asteroid]]s, and [[meteor]]oids. If such ejected water and mud fell to Mars from above, then they might have held [[microbes]]--and therefore any microbes found on Mars are far more likely to have come from earth during the Noachic Flood than to have originated on Mars.<ref>If such life forms survived, that need not be a great shock to any observer. [[Extremophiles]], or microbes known to thrive under conditions that would kill or render dormant any other form of life, are well-known on earth and have even been the subject of engineering studies attempting to find practical uses for them.</ref>

|[[Einstein]]'s explanation is a refinement of Newton's explanation of gravity. Einstein's explanation is currently the most accepted explanation of the fact of gravity. || The [[modern evolutionary synthesis]] is a refinement of Darwin's explanation of evolution. This modern synthesis is currently the most accepted explanation of the fact of evolution.

 

Space scientists have searched for extraterrestrial microbes for years. To date, no definitive proof of such microbes has been found. The Antarctic meteorite mentioned above, and the alleged bacterial fossils on it, fueled speculation for months, until other scientists finally determined that the microbes involved probably were earthly contaminants.<ref>Rick Lockridge, "[http://www.cnn.com/TECH/9801/15/contaminated.rock/ Scientists dispute NASA's claims about Mars meteorite]", ''The Cable News Network'', January 15, 1998. Retrieved April 17, 2007 from CNN's web servers.</ref>

|Einstein's explanation of the fact of gravity is called ''The General theory of relativity''. ||The explanation of the fact of evolution provided by the modern synthesis is the latest and most widely accepted ''Theory of Evolution''.

 

Nevertheless, the finding of extraterrestrial microbes on [[Mars]] is one of the fondest expressed hopes of NASA planetary scientists<ref>Authors unknown, "[http://mars.jpl.nasa.gov/life/ Do Martians Exist?], ''NASA Mars Exploration'', 05 Oct 2005 04:51:40 UTC. Retrieved April 17, 2007, from [[NASA]].</ref> and of other scientists and advocacy groups<ref>Everett Gibson, Jr., David S. McKay, and Kathie Thomas-Kerpta, "[http://www.marssociety.org/portal/TMS_Library/MAR_98_046/view Life on Mars: Evidence from Martian Meteorites]," ''Proceedings of the Founding Convention of the Mars Society'', R. M. Zubrin and M. Zubrin, eds. 1998. Retrieved April 17, 2007, from [http://www.marssociety.org The Mars Society].</ref> hoping to persuade the [[United States]] government, or perhaps the [[United Nations]], to fund crewed expeditions to Mars. Furthermore, no sane space mission planner could in good conscience ignore the potential hazard of the transport of a microbe to earth and the release of that microbe into earth's [[biosphere]]. Happily, measures for containing such a microbe, perhaps derived from those measures taken during [[Project Apollo]], would contribute a relatively insignificant amount to the total budget of a program of crewed missions to Mars or to any other celestial body.

!style="background:#d0e5f5;color:black" |Gravity is a fact and a theory.!!style="background:#d0e5f5;color:black" |Evolution is a fact and a theory.   

 

[[Francis Crick]] and [[Leslie Orgel]], in 1973,<ref>Crick, F. H. C., and Orgel, L. E. "Directed Panspermia," ''Icarus'', 19, 341 (1973).</ref> openly speculated on a form of exogenesis called [[Panspermia#Directed panspermia|directed panspermia]], in which such an extraterrestrial nation-state fired a brace of missiles, each laden with [[bacteria]] and/or [[blue-green algae]], in all directions. One such  missile crashed on earth, and we are its by-product, as it were, their theory states.<ref>For a detailed discussion on the logical weaknesses and omissions of such a position, see the main article on [[Panspermia]].</ref>

 

Besides [[Earth]] there are two moons and one planet that scientists consider possibly habitable to some form of life.

#The [[Jupiter|Jovian]] moon [[Europa (moon)|Europa]] is covered with a thick sheet of ice. Scientists speculate that a liquid ocean may exist under the crust and that may harbour life.

#[[Titan]], a moon of [[Saturn]], has approximately the same percentage of [[nitrogen]] in its atmosphere as in Earth's. Titan also has [[ocean]]s and thick clouds. Scientists have determined that the oceans are liquid [[methane]], not water, and that the low temperatures of -178° Celsius make life, at least as we know it, highly improbable.

 

Do one or more extraterrestrial civilizations exist? Until recently, speculation about extraterrestrial races was confined either to [[science fiction]] or to innumerable anecdotal reports of "[[UFO|unidentified flying objects]]." These latter reports were once the subject of an investigation, known as [[Project Blue Book]], by the [[United States Air Force]].<ref>Anonymous, "[http://www.ufoevidence.org/topics/ProjectBlueBook.htm Project Blue Book]", ''[http://www.ufoevidence.org/ UFO Evidence.org]'', retrieved April 16, 2007</ref><ref>Anonymous, ''[http://www.bluebookarchive.org/ The Project Blue Book Archive]'', retrieved April 16, 2007</ref><ref>Fund for Unidentified Flying Object Research (FUFOR), ''[http://www.nicap.org/index.htm Official Site of the National Investigative Committee for Aerial Phenomena]'', Francis L. Ridge, editor and Webmaster, December 15, 1997 to present. Retrieved April 16, 2007.</ref><ref>Presumably the [[Union of Soviet Socialist Republics|Soviet]] Army Air Forces had their own version of Blue Book as well.</ref> But years after Blue Book wound down, a large cadre of scientists began to entertain seriously the notion that extraterrestrial civilizations might exist.

 

SETI ('''S'''earch for '''E'''xtra'''t'''errestrial '''I'''ntelligence)<ref>[http://www.seti.org/site/pp.asp?c=ktJ2J9MMIsE&b=178025 Home of the SETI Institute]</ref> is the name given to several government and privately-funded projects that over the years have searched for evidence of extraterrestrial civilizations. This is done by listening via [[radiotelescope]] on a defined frequency band for any transmission having any semblance of order. The frequency band is one that, they believe, is the likeliest region in the [[electromagnetic spectrum]] for anyone to be sending a signal intended to cross interstellar, or even intergalactic, space.

 

No definitive evidence exists for any form of extraterrestrial civilization. While the [[Project Blue Book]] investigators found a number of cases that they had to classify as "unknown," they were able to classify the bulk of the anecdotes as anything from outright hoaxes to misinterpretations of common weather features to misinterpretation of the sightings of ordinary aircraft.<ref>The Air Force might also have acted in a deceptive manner in certain isolated cases in which what the witnesses took for [[UFO]]s were actually secret experimental prototypes. Perhaps some of these prototypes exist today as the [[B-2]], [[F-117]], and other [[Stealth aircraft]].</ref> Neither has any [[Astronomy|astronomer]] or [[astronaut]] reported a definite sighting of, much less contact with, any carrier-like vessel that would have been capable of launching any of the alleged two-seater or similar small-crewed craft that various "witnesses" report having encountered. Nor has any [[physics|physicist]] yet suggested a method by which such a craft could have visited our [[solar system]], given the fixed speed limit set by the [[Special Theory of Relativity]]. Finally, the SETI project, for all their searching for a signal (even to recruiting civilians to participate in a "distributed computing" project to process the noise they have received from their radiotelescopes), have never isolated anything like a definite signal.

 

====The Drake Equation====

In 1961, astronomer Frank Drake developed a method for estimating of the number of extraterrestrial civilizations in the galaxy.  The Drake Equation simply begins with the number of stars, then multiplies that number by a series of probabilities (probability that a star has planets, that a planet can support life, etc.) to obtain the quantity desired (number of populated planets, number of civilizations whose existence is detectable, etc.).

 

In principle, the Drake Equation can provide an upper and lower bound for the number of extraterrestrial civilizations by setting upper and lower bounds for each probability factor, which can then be improved upon as better information becomes available. Because the number of stars in so huge, even the lower bound is often calculated to be a respectable number.  However, a serious problem is that some of the probabilities are completely unknown, or even unknowable. For example, the probability of life emerging on a planet is a meaningless concept if life is created directly by God and not by some naturalistic process.

 

If any of the probabilities appearing in the equation is zero, then the number of extraterrestrial civilizations of course goes to zero.  This is a serious problem if one relies only on naturalistic explanations of the genesis of life.  One of the most well-accepted scientific laws, the [[law of biogenesis]], says that life only comes from life, which means that it cannot come from non-life.  Furthermore, scientific observations are that evolution itself is impossible, as evolution requires ''increasing'' genetic [[information]], whereas observations show that living things ''lose'' genetic information.<ref>Wieland, Carl, [http://www.creationontheweb.com/content/view/431/ The evolution train’s a-comin’], ''Creation'' 24(2):16–19, March 2002.</ref>

== Extraterrestrial Life in Science Fiction ==

== Extraterrestrial Life in Science Fiction ==