Carbon chauvinism is aneologism meant to disparage the assumption that the chemical processes of hypotheticalextraterrestrial life must be constructed primarily fromcarbon (organic compounds) because as far as is known, carbon's chemical andthermodynamic properties render it far superior to all other elements at forming molecules used in living organisms.[1]
The expression "carbon chauvinism" is also used to criticize the idea thatartificial intelligence cannot in theory besentient or truly intelligent because the underlying matter is not biological.[2] Furthermore, the term is used bytranshumanists to object to the commonly held view that life has an inherently highermoral value than hypotheticalartificial consciousness.[3]
The term was used as early as 1973, when scientistCarl Sagan described it and other humanchauvinisms that limit imagination of possible extraterrestrial life.[4] It suggests thathuman beings, as carbon-based life forms who have never encountered any life that has evolved outside the Earth's environment, may find it difficult to envisionradically different biochemistries.[5]
Like carbon,silicon can form four stable bonds with itself and other elements, and long chemical chains known assilane polymers, which are very similar to thehydrocarbons essential to life on Earth. Silicon is more reactive than carbon, which could make it optimal for extremely cold environments.[6] However, silanes spontaneously burn in the presence of oxygen at relatively low temperatures, so an oxygen atmosphere may be deadly to silicon-based life. On the other hand, it is worth considering thatalkanes are as a rule quite flammable, but carbon-based life on Earth does not store energy directly as alkanes, but as sugars, lipids, alcohols, and other hydrocarbon compounds with very different properties. Water as a solvent would also react with silanes, but again, this only matters if for some reason silanes are used or mass-produced by such organisms.
Silicon lacks an important property of carbon: single, double, and triple carbon-carbon bonds are all relatively stable.Aromatic carbon structures underpinDNA, which could not exist without this property of carbon. By comparison, compounds containingsilene double bonds (such assilabenzene, an unstable analogue ofbenzene) exhibit far lower stability than the equivalent carbon compound. A pair of silane single bonds have significantly greater totalenthalpy than a single silene double bond, so simple disilenes readily autopolymerise, and silicon favors the formation of linear chains of single bonds (see thedouble bond rule).
Hydrocarbons and organic compounds are abundant in meteorites, comets, and interstellar clouds, while their silicon analogs have never been observed in nature. Silicon does, however, form complex one-, two- and three-dimensional polymers in which oxygen atoms form bridges between silicon atoms. These are termedsilicates. They are both stable and abundant under terrestrial conditions, and have been proposed as a basis for a pre-organic form of evolution on Earth (seeclay hypothesis).
