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To my understanding, Pasteur’s experiment demonstrates that life is only made from life. If this is true, then how could origin of life (aka. abiogenesis) ever have happened?

It seems to me that Pasteur’s experiment and the theory according to which there is abiogenesis contradict each other. Do they?

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  • $\begingroup$ If I may, your goal should not be to try to convince your friend but to understand whether the meaning of Pasteur's experiments on evolutionary biology. $\endgroup$ – Remi.b Mar 15 '18 at 22:52
  • $\begingroup$ @Remi.b Well yes, that is what I thought. It's not my primary goal to convince my friend, but to understand where I misinterpreted it $\endgroup$ – Ayy Lmao Mar 15 '18 at 22:57
  • $\begingroup$ Please describe briefly Pasteur's (note the apostrophe) experiment. Without it your question is meaningless and you cannot start thinking logically about what his experiment demonstrated (I presume that the cause of food spoiling by bacterial growth is not due to "spontaneous generation"). You can only argue about science with someone if you understand and define what you are talking about. $\endgroup$ – David Mar 15 '18 at 23:04
  • $\begingroup$ @AyyLmao I've edited you post to try to highlight your interest and not the argumentation you're having with your friend. Feel free to roll back if you don't like the edit. $\endgroup$ – Remi.b Mar 15 '18 at 23:05
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    $\begingroup$ Pasteur's experiment does not demonstrate that life is only made from life (even if he might have thought it did). It simply demonstrates that life does not arise under the conditions of his experiment, during the short time available. You might also note that if he'd had some thermophiles en.wikipedia.org/wiki/Thermophile in the flasks, he might well have gotten different results :-) $\endgroup$ – jamesqf Mar 16 '18 at 4:19
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Pasteur’s experiments demonstrated that the appearance of living matter in spoiled food (soured wine and the like) was not due to so-called spontaneous generation of living organisms, but due to the multiplication of pre-existing but invisible micro-organisms, which could be eliminated by sterilization of the food containers — hence the term pasteurization used (in Britain, at least) for the sterilization of milk.

No more, no less. His experiments say nothing about, and were not concerned with, the origin of life on earth. They related solely to the vitalist misinterpretation of everyday observations in 19th century France. As far as I am aware, Pasteur never concerned himself with Darwin’s theory of evolution. French and British science (and Pasteur and Darwin) had different philosophies and emphases at that time, and contacts were limited.

One may ask what is the difference between abiogenesis and spontaneous generation. The former envisages a slow series of chemical processes leading over millions of years to the first self-replicating molecules and subsequently to simple single-celled organisms — an idea that only really gained traction after the Miller-Urey experiment. The latter involves fully developed organisms appearing out of nothing in a couple of days — a sort of arbitrary non-Christian version of creationism.

The scientists who developed the the idea of an origin of life from inorganic matter were well aware of the significance of the work of Pasteur. They were also aware of the subsequent progress of chemistry and biochemistry. It is worth mentioning that Pasteur was so concerned with repelling the vitalist viewpoint (a sort of irrational superstition akin to belief in magic) that when Büchner demonstrated glucose metabolism in yeast extracts containing no living cells he wrongly rejected this. (The word enzyme means in yeast.)

You can read about Pasteur and Spontaneous Generation here, and Büchner and the Liebig–Pasteur dispute here. There is also a long Wikipedia entry on Pasteur — the French version is even more extensive. You can read about his supposed religious views here if you are interested, but you should remember that the views of a scientist, however famous, are only of scientific value if they are supported by his experiments.

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Consider the context. In Antiquity and the Middle Ages from Aristotle on, people thought that many living things (from microbes to mice) would arise through spontaneous generation. Seemed sensible enough; if you don't pay close attention to animals getting somewhere, and you have no knowledge of anything microscopic, it can easily look like animals just come out of the environment. After the Enlightenment scientists got better understandings of reproduction on the one hand, and made many experiments showing that under certain conditions (like keeping meat sealed so flies couldn't get to it for example), life didn't, in fact, spontaneously generate in the way it was previously thought it did. At this point the idea that all living things come from the reproduction of other living things of the same species became increasingly accepted.

Pasteur's experiment was more or less the death knell of the spontaneous generation hypothesis; some previous experiments had shown microbes growing after a flask was supposedly sterilized, or kept the flask sterile by keeping air out (which opened one to the argument that spontaneous generation required air). His showed microbes not growing in a flask where air could flow but dust did not settle because of its shape, and immediately growing when the flask was tipped and dust fell in.

Pasteur's experiment didn't so much "prove that life only comes from life", as disprove a specific other hypothesis that existed at the time. And in that sense it is still consensus biology: No biologist today thinks that snakes, mice, microbes, or even viruses can arise directly through abiotic processes. If you replace "life" with "modern life", the principle is true as far as we know.

Now biology has advanced a lot, and there is a different context, with people asking different questions and advancing different hypotheses to answer them. The question of the origin of life is one such question, that has nothing to do with what Pasteur was trying to prove. And that's where the "modern life" caveat becomes relevant; while all modern living things are too complex and specific to arise directly via abiotic processes, it doesn't follow that the same is true of the first living things. We know that living things used to be different from how they are now; and in fact when looking into the past via the fossil record and genetic evidence we find clear patterns of gradual development of the modern biosphere's diversity and complexity from simpler and more generic ancestors. While it is harder to find evidence for the evolution of early cells, because the genetic evidence is muddled by the time scales involved and the fossil evidence near-nonexistent for obvious reasons, it is sensible to figure that similar patterns would occur there, and that the earliest cells were as different and simpler than a modern cell as a Precambrian worm is from us.

Here is a video of Nick Lane talking about a promising hypothesis on the origin of life. It sort of illustrates how different, and simpler, those primordial living things could have been compared to current organisms.

https://www.youtube.com/watch?v=gb7pZyks_HE&t=1151s

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Pasteur proved that modern lifeforms can't form from non-living things. That doesn't prove that there is some hard and bright line that prevents a micell containing enzymatic RNA from changing a bit into something we would recognize as "life".

Does your friend know about Friedrich Wöhler? Who synthesized urea in a test tube, proving that the chemistry of life is not fundamentally different to the rest of chemistry?

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