Charles Darwin was one of the first scientists to theorize on the function of the appendix, which in his day had been identified only in humans and other great apes. He hypothesized that the distant ancestors of these animals survived on a diet of leaves, and so they required a large cecum, a portion of the gut that houses bacteria that can break down stubborn plant tissue. Later, he speculated, these ancestors shifted to a largely fruit-based diet that was easier to digest. A large cecum was no longer necessary, and it began to shrink...Darwin thought the appendix, which juts off of the cecum, is one of its former folds that shriveled up as the cecum shrank. Consequently, he thought it carried no function.

I recently read a source which states the above. It made me wonder that if there is some other organ/part in our body which may shrink as further evolution progresses and it's use diminishes, just like our appendix. I'd like to know if this 'theory of shrinking' applies to any organ that may become useless.

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    $\begingroup$ If you read the Wikipedia article on the appendix, you'll see that the hypothesis of vestigiality is simply incorrect. It is quite important in maintaining the balance of flora in the gut, and also plays an important role in immunity. Remember, Darwin lived 150 years ago, and not everything he proposed was correct. Even Einstein was wrong on occasion. $\endgroup$ – MattDMo Sep 10 '16 at 17:41
  • $\begingroup$ Reading your title you seem to be talking about development, while the post is about evolution. You should check the definitions of these two terms if they are unclear to you. $\endgroup$ – Remi.b Sep 10 '16 at 17:42
  • $\begingroup$ If you were interested about development (but I doubt you are), muscles and bones would be good examples. $\endgroup$ – Remi.b Sep 10 '16 at 17:42
  • $\begingroup$ You should link to the original article you are quoting. $\endgroup$ – Remi.b Sep 10 '16 at 17:43
  • $\begingroup$ @MattDMo I've read this article thrice but nowhere does it state for sure that the appendix DOES HAVE THIS FUNCTION ONLY and without it our body will suffer complications. Not just Wikipedia, but almost every site uses the phrase '...may have this function' or 'may house good bacteria...' far too much. And Huffington Post still states it's function to be 'in much debate'. $\endgroup$ – Irena Sep 16 '16 at 11:51

First of all, our appendix isn't 'useless'. Their is a high concentration of lymph nodes (higher than anywhere else in your gut), so it might not be needed for digestion anymore, but it's function somewhat shifted to a more immunological role. Secondly, yes there are other organs/body parts that shrink over time. In evolutionary time, look at our tailbone. In monkeys it's still a full tail, in apes it's almost nothing, and in humans it's still present in the skeleton, but not visible on the 'outside' anymore. Probably in a few (hundred/thousand/..) years it will be completely reduced until it is no longer present in the human skeleton (because since we don't have a tail anymore, it doesn't have any function anymore). Over a much shorter timescale it is also possible. For example the thymus expands in puberty, and afterwards it shrinks until it is almost completely gone.

  • $\begingroup$ The thymus does not shrink because of vestigiality or lack of use. It is simply part of the development of the immune system, that T cell maturation and development moves from it elsewhere, like the lymph nodes, spleen, and bone marrow. You already repeated what I said much earlier about the appendix. Finally, the coccyx is certainly not without function. It serves as an attachment site for ligaments, muscles, and tendons, and is an insertion point for muscles in the pelvic floor. It is also important for stabilization when you're sitting. $\endgroup$ – MattDMo Sep 11 '16 at 15:00

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