Evolutionary biology has gone from thinking life will arise on any planet with the right conditions, to the realization that life's arising out of nonlife is likely a very rare occurrence. This paper suggests life may have originated once in our galaxy and spread by interstellar comets and asteroids carrying genetic material to all of its corners over billions of years.
What this would mean is that all life in the galaxy is interrelated, and if we find life on Mars, Enceladus, Titan, Galileo, etc. we will find that they're our cousins rather than something totally alien. It also means as suggested in the following quote that we will find the forms and natural selection of life elsewhere will not be so alien that we won't recognize it as life.
Of particular interest to the readers of this group is the suggestion that phenomena like the Cambrian Explosion and the sudden emergence of octopod intelligence may be the result of genetic material coming into the Earth's biosphere from elsewhere in the galaxy. Cue theme from Ridley Scott's Prometheus.
Quote:
...With the rapidly increasing number of exoplanets that have been discovered in the habitable zones of long-lived red dwarf stars (Gillon et al., 2016), the prospects for genetic exchanges between life-bearing Earth-like planets cannot be ignored. In our view the idea of life emerging de novo in multiple locations through a process of in situ abiogenesis appears far-fetched and merely compounds the difficulty of a single origination on the Earth. The internal evidence from terrestrial biology that we have discussed in this paper suggests that the entire ensemble of habitable planets in the galaxy constitutes a single interconnected biosphere. Lifeforms elsewhere, on this viewpoint, will be expected to exhibit a converging pattern of genotypes and phenotypes, subject to natural selection (Darwinian and Lamarckian) within individual planetary habitats. ...
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Source:
https://www.sciencedirect.com/scienc...79610718300798