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Are there processes in the human body which occur via natural selection among cells? Could anyone provide examples?

E.g. when tissues are conditioned to be stronger, such as a rock climber's skin getting thicker, would that be natural selection at work? What about muscle conditioning via lifting weights?

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    $\begingroup$ Please read about natural selection; the process requires reproduction of the organism. For that reason, it's not possible among an individual's cells. Cells have distinct purposes. They don't compete. $\endgroup$ Commented Jul 31, 2021 at 23:16
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    $\begingroup$ Cancerous tumors... $\endgroup$
    – Roger V.
    Commented Aug 1, 2021 at 10:06
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    $\begingroup$ @anongoodnurse Whether we call it natural selection or not, I see no reason why cells can't compete for survival under some contexts, and become enriched in a population in virtue of particular genes. I can also imagine this process happening in the absence of higher-level regulatory / tissue-level processes, but I was just wondering if people had examples. I think Roger's example of cancerous tumours will sometimes be one such case. $\endgroup$
    – derek1984
    Commented Aug 3, 2021 at 5:02
  • $\begingroup$ Normally cells work together for the good of the whole. Cancerous cells certainly compete/outcompete, but that's not normal. $\endgroup$ Commented Aug 3, 2021 at 21:37
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    $\begingroup$ @anongoodnurse — My understanding is that natural selection can operate at multiple levels including at the cellular level. That previous source specifically mentions cancer, so I don't think the distinction you are making reflects current usage in evolutionary biology. $\endgroup$
    – tyersome
    Commented Aug 11, 2021 at 22:53

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Arguably T cell maturation in the thymus is such a process.

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  • $\begingroup$ That's an interesting example. +1 I'm not sure, though, that a normal process of elimination or enhancement qualifies it as natural selection. Maybe it does, but it would raise a lot of questions about what, exactly, the definition is. Are younger RBCs selected for O2 carrying because older RBCs are being picked off by the spleen? Etc. $\endgroup$ Commented Aug 3, 2021 at 21:41
  • $\begingroup$ T cell maturation involves generating an enormous surplus of immature T cells with recombination and enhanced mutation in the receptor genes. Among those the body retains only those with binding affinity to certain molecules within a given range, killing off the majority that have too high or too low binding affinity. Thus, cells divide to form a large initial population, which is then severely winnowed by selection to produce the final population that emerges into the body. Some cells then undergo further clonal selection upon immune challenge. This seems like natural selection to me. $\endgroup$
    – Armand
    Commented Aug 3, 2021 at 23:14
  • $\begingroup$ I understand the process. My comment stands. $\endgroup$ Commented Aug 4, 2021 at 12:56

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