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An [[infinite regression]] is a proposed chain of causation in which each purported cause itself requires another event of exactly the same type to cause ''it.''

An [[infinite regression]] is a proposed chain of causation in which each purported cause itself requires another event of exactly the same type to cause ''it.''

This raises the question of what set the original chain in motion--in short, what was the "first cause." Whether all things must have a "first cause" or not, is a subject of [[Is a first cause of a process necessary, always possible, or sometimes impossible?|debate]].

This raises the question of what set the original chain in motion--in short, what was the "first cause." Whether all things must have a "first cause" or not, is a subject of [[Debate:Is_a_first_cause_of_a_process_necessary%2C_always_possible%2C_or_sometimes_impossible%3F|debate]].

== An example ==

== An example ==

Many [[sciece|scientists]], observing the remarkable complexity of life (and especially of [[DNA]], the [[molecule]] that holds the complete instruction set for life), doubt strenuously that life could have originated on the earth out of non-life--a process called [[abiogenesis]]. [[Francis H. Crick]], the co-discoverer of [[DNA]], recognized this early and also is alleged to have recognized other conditions that abiogenesis would have required, that in all [[probability]] did not exist on earth. Crick did not believe that life was created by supernatural means, and therefore deduced that since life did ''not'' originate on earth, it was ''deposited'' on earth from outside.

Many [[scientist]]s, observing the remarkable complexity of life (and especially of [[DNA]], the [[molecule]] that holds the complete instruction set for life), doubt strenuously that life could have originated on the earth out of non-life--a process called [[abiogenesis]]. [[Francis H. Crick]], the co-discoverer of [[DNA]], recognized this early and also is alleged to have recognized other conditions that abiogenesis would have required, that in all [[probability]] did not exist on earth. Crick did not believe that life was created by supernatural means, and therefore deduced that since life did ''not'' originate on earth, it was ''deposited'' on earth from outside.

How, then, did this happen? Most proponents of his outside-seeding of life, called [[panspermia]], suggest that the [[comet]]s contain the seeds of life within their tails, and the earth acquired these seeds by passing through a comet's tail. Dr. Crick and his colleague [[Leslie H. Orgel]] assumed something far more radical: that an advanced [[civilization]] built and launched a brace of intergalactic [[ballistic missile]]s, each laden with bacteria and blue-green algae, in all directions from their homeworld. One such missile crash-landed on earth, and all life on earth is the by-product of the payload of that missile.

How, then, did this happen? Most proponents of his outside-seeding of life, called [[panspermia]], suggest that the [[comet]]s contain the seeds of life within their tails, and the earth acquired these seeds by passing through a comet's tail. Dr. Crick and his colleague [[Leslie H. Orgel]] assumed something far more radical: that an advanced [[civilization]] built and launched a brace of intergalactic [[ballistic missile]]s, each laden with bacteria and blue-green algae, in all directions from their homeworld. One such missile crash-landed on earth, and all life on earth is the by-product of the payload of that missile.