# Life only arose once on Earth? **URL:** \ **Category:** Factual Questions\ **Created:** [July 19, 2003, 10:15pm UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648 "2003-07-19T22:15:36Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Earthling](https://avatars.discourse-cdn.com/v4/letter/e/90db22/32.png) [@Earthling](https://boards.straightdope.com/u/Earthling)\ **Post date:** [July 19, 2003, 10:15pm UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648/1 "2003-07-19T22:15:36Z")
So, I’m reading _Life_, Richard Fortey’s book on paleontology, and also looking on the [web](http://www.ucmp.berkeley.edu/clad/clad1.html) to expand my knowledge. Anyway, it seems that a fundamental assumption of evolutionary biology is that life only arose once and everything else proceeded from there forward. I can understand how the mechanics of evolutionary theory mean that everything must point back to a single starting state, but why is that so? In other words, what in the early days of our planet prevented multiple geneses? Wouldn’t it be possible for the organic chemical reactions that produced the first amino acids to have happened more than once, in multiple locations? Or, similarly, for the formation of RNA and other building blocks of life? Would we be able to tell the difference today if that is indeed what happened? Or am I just confused? ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [July 19, 2003, 10:32pm UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648/2 "2003-07-19T22:32:11Z")
Here is an earlier thread on this subject: [http://boards.straightdope.com/sdmb/showthread.php?threadid=170352](http://boards.straightdope.com/sdmb/showthread.php?threadid=170352) ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [July 19, 2003, 10:32pm UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648/3 "2003-07-19T22:32:11Z")
No, I don’t think you’re confused. A multiple genesis scenario is possible, as is another your question prompted in my mind, that being life beginning and then dying out, and then starting again. ---
**Author:** ![Earthling](https://avatars.discourse-cdn.com/v4/letter/e/90db22/32.png) [@Earthling](https://boards.straightdope.com/u/Earthling)\ **Post date:** [July 19, 2003, 11:15pm UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648/4 "2003-07-19T23:15:26Z")
Thanks. I just read the linked thread, and it appears that there’s nothing to prevent multiple geneses from happening, but eventually one set of “organisms” won and wiped everyone else out. Makes sense. What gets me confused is passages in Fortey’s book such as (pp. 35-36): > [@](#): > > But then, if this extraordinary natural splicing of carbon-bearing molecules could happen once, could it not have happened more than once – or even many times?..If this first concoction of life were not miraculous then it could have been merely routine. This being the case, life could have sprung up independently in one or another organism…But we cannot escape the brotherhood of lower invertebrates so easily… > > Meccano is a construction system that uses struts and bars and nuts and bolts and little more, but working models of the Eiffel Tower can be made from it. Life [in the views of some?] could be seen as a kind of auto-constructing Meccano of inconceivable complexity – but, at bottom, still Meccano, which can be deconstructed into a box or two of tricks and a manual. > > I find it difficult to visualize life in these terms, even though this kind of reductionist view has claimed many (perhaps all) of the great victories in its understanding. Which sounds to me like he’s saying that it is only possible for life to arise once, not that it may have happened many times but only one form survived. It also sounds like he thinks that the creation of life on Earth is somehow miraculous, but perhaps that is just hyperbole for “against long odds.” ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [July 20, 2003, 12:29am UTC](https://boards.straightdope.com/t/life-only-arose-once-on-earth/189648/5 "2003-07-20T00:29:09Z")
Let’s face it; there is no evidence one way or the other. What is known is that life arose pretty much as soon as the earth cooled enough for it to be viable, which suggests to me that the odds are not long and therefore that it likely happened only once. On the other hand there is one and only one genetic code and that points to the likelihood that all life around now goes back to one origin. The reason for that is that the genetic code is essentially arbitrary. For an analogy, think of the fact that hominid apes seemed to evolve a number of times, maybe as many as a dozen, but they all died out, except one. So one can fairly conclude that starting from the great apes that existed in Africa 10 or 12 million years ago, it was quite likely that some sort of hominid would evolve, but not necessarily homo sap.