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I was surprised to learn that the vas deferens detours over the pubic bone instead of taking the obviously more direct path.

https://human.biodigital.com/widget?be=u1P&uaid=1ly5V

Because I would assume that the vas deferens is more prone to damage facing the front. Also its damage would put procreation at stake.

Hence my question: Is there a biological reason for this path? Some advantage which outweighs or balances its disadvantages?

enter image description here

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  • $\begingroup$ What do you consider the "obviously more direct path"? The vas deferens has to pass over the pelvis somehow to get back to the level of the prostatic urethra. Remember that the vas deferens travels with a number of other structures (vessels/nerves) in the "spermatic cord". $\endgroup$ – Harry Vervet Feb 17 '16 at 16:36
  • $\begingroup$ okay, probably I am being a bit naive here - I didn't study medicine or biology, after all. But just visualize your own reproductive system and think of direct path between testicles and prostate. That path would be a third or less of the actual - so this is what I wonder about. And the solid pelvic bone in the back increases the risk of damage in case of a hit from the front. $\endgroup$ – Raffael Feb 17 '16 at 16:46
  • $\begingroup$ The path of the human vas deferens is a similar example. from Reddit AMA with Richard Dawkins So (at least) according to Dawkins the path which the vas deferens takes is simply an evolutionary "mistake". $\endgroup$ – Raffael Jun 6 '16 at 8:12
  • $\begingroup$ You may want to look at where the abdominal muscles are, since they have go around them to get out of the body cavity. $\endgroup$ – John Mar 15 at 16:29
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The vas deferens following this seemingly odd path is just a result of the natural course of our evolution. Millions of generations ago, our ancestors were quadrapedal (walked on all four limbs). Similar to if you were to crawl on your hands and knees today. In this position the pelvis is rotated forward by ~90 degrees from its position in humans currently. The natural position of the testicles in this position would be to hang straight down due to gravity. Which means the vas deferens would have a straight path up in front of the pubic bone.

Generation after generation, our taller and more upright ancestors were able to survive slightly better than their less upright siblings. Meaning that many of the more quadrapedal siblings died while their more upright siblings survived and reproduced. This process has continued for millions of generations, leading to our current homonid upright posture. The path of the vas deferens was established long before our ancestors ever began this slow transition toward standing vertically. So the vas deferens still follows the same path that it always has, but now our testicles have moved down because we stand vertically. Which leaves the vas deferens with its seemingly odd route of going forward over the pubic bone and then down to the testicles. Evolution is a continuous incremental process over the course of millions of generations. There has been no point at which the vas deferens could be 'unplugged' and rerouted around the pubic bone. So it now just loops in front of the pubic bone and then to its destination. Richard Dawkins used the word "mistake" in his description because there is not necessarily an advantage to that particular route of the vas deferens(there may even be small disadvantages), but there was a LARGE advantage to our ancestors standing upright. So as we evolved to stand more upright, the testicles moved down appropriately and the vas deferens just ended up where it is, simply because that's where it always has been. Not really a mistake, just the way it worked out. Hope this is helpful.

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    $\begingroup$ Welcome to Biology.SE! This looks it might be the start of a good answer, but answers are much more likely to receive a favorable response if you include supporting references (primary literature is best). Without that support, your answer is indistinguishable from opinion. In particular if some or all of this is a quotation, please credit your source. This is a good example of how to format references. ——— Please take the tour and then consult the help pages for additional advice on How to Answer effectively on this site. Thank you! 😊 $\endgroup$ – tyersome Oct 15 '20 at 21:33

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