Editing Panspermia (section)

=== Directed panspermia ===
{{Main|Directed panspermia}}

First proposed in 1972 by Nobel prize winner [[Francis Crick]] along with [[Leslie Orgel]], directed panspermia is the theory that life was deliberately brought to Earth by a higher intelligent being from another planet.<ref name=":7">{{Cite journal |last1=Crick |first1=F. H. C. |last2=Orgel |first2=L. E. |date=1973-07-01 |title=Directed panspermia |url=https://dx.doi.org/10.1016/0019-1035%2873%2990110-3 |journal=Icarus |volume=19 |issue=3 |pages=341–346 |doi=10.1016/0019-1035(73)90110-3 |bibcode=1973Icar...19..341C |issn=0019-1035}}</ref> In light of the evidence at the time that it seems unlikely for an organism to have been delivered to Earth via radiopanspermia or lithopanspermia, Crick and Orgel proposed this as an alternative theory, though it is worth noting that Orgel was less serious about the claim.<ref>{{Cite book |last=Plaxco |first=Kevin |url=http://dx.doi.org/10.56021/9781421441306 |title=Astrobiology |date=2021 |publisher=Johns Hopkins University Press |doi=10.56021/9781421441306 |isbn=978-1-4214-4130-6}}</ref> They do acknowledge that the scientific evidence is lacking, but discuss what kinds of evidence would be needed to support the theory. In a similar vein, [[Thomas Gold]] suggested that life on Earth might have originated accidentally from a pile of 'Cosmic Garbage'  dumped on Earth long ago by extraterrestrial beings.<ref>{{Cite book |last=Gold |first=Thomas |chapter=Reasons for expecting subsurface life on many planetary bodies |editor-first1=Richard B. |editor-last1=Hoover |date=1997-07-11 |title=Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms |chapter-url=http://dx.doi.org/10.1117/12.278775 |series=SPIE Proceedings |volume=3111 |pages=7–14 |publisher=[[SPIE]] |doi=10.1117/12.278775|s2cid=97077011 }}</ref> These theories are often considered more science fiction, however, Crick and Orgel use the principle of cosmic reversibility to argue for it.

This principle is based on the fact that if our species is capable of infecting a sterile planet, then what is preventing another technological society from having done that to Earth in the past?<ref name=":7" /> They concluded that it would be possible to deliberately infect another planet in the foreseeable future. As far as evidence goes, Crick and Orgel argued that given the universality of the genetic code, it follows that an infective theory for life is viable.<ref name=":7" />

Directed panspermia could, in theory, be demonstrated by finding a distinctive 'signature' message had been deliberately implanted into either the [[genome]] or the [[genetic code]] of the first microorganisms by our hypothetical progenitor, some 4 billion years ago.<ref>{{Citation |last=Marx |first=George |title=Message through time |date=1979 |url=http://dx.doi.org/10.1016/b978-0-08-024727-4.50021-4 |work=Communication with Extraterrestrial Intelligence |pages=221–225 |access-date=2023-12-08 |publisher=Elsevier|doi=10.1016/b978-0-08-024727-4.50021-4 |isbn=9780080247274 }}</ref> However, there is no known mechanism that could prevent [[mutation]] and [[natural selection]] from removing such a message over long periods of time.<ref name=":122">{{Cite journal |last1=Yokoo |first1=Hiromitsu |last2=Oshima |first2=Tairo |date=April 1979 |title=Is bacteriophage φX174 DNA a message from an extraterrestrial intelligence? |url=http://dx.doi.org/10.1016/0019-1035(79)90094-0 |journal=Icarus |volume=38 |issue=1 |pages=148–153 |bibcode=1979Icar...38..148Y |doi=10.1016/0019-1035(79)90094-0 |issn=0019-1035}}</ref>

==== Counterarguments ====
In 1972, both abiogenesis and panspermia were seen as viable theories by different experts.<ref name=":44"/> Given this, Crick and Orgel argued that experimental evidence required to validate one theory over the other was lacking.<ref name=":7" /> That being said, evidence strongly in favor of abiogenesis over panspermia exists today{{Citation needed|date=October 2024}}, whereas evidence for panspermia, particularly directed panspermia, is decidedly lacking.