Nor is the Spleen Vestigial

Long ago, the spleen was thought to be the storehouse of anger, so ranting and such was considered "venting" it. Ridiculous idea, and bad psychology (because one is practicing rage instead of restraint). Another bad idea is that the spleen was vestigial, i.e., leftover from our evolutionary past.

Credit: Wikimedia Commons / Scientific Animations (CC BY-SA 4.0)

As with many other so-called vestigial organs/structures, since people did not understand its function, the spleen was considered unimportant. That's an argument from ignorance, old son. If people weren't so willing to let evolutionary thinking cause harm to medical science, they might realize that the Master Engineer put things in place for a purpose. Find out what it does before calling it useless (and in many cases, performing harmful surgeries). The spleen actually has important functions, and not all are fully understood yet.

A review of vestigial claims of the human spleen reports no clear evidence for its function until the late 1950s. It is now acknowledged to be a critical organ serving at least six different important functions. Furthermore, the spleen exists universally in jawed vertebrates and is not found in any invertebrates, so it has no evolutionary history. The lack of evidence for simpler or transitional forms of the spleen supports the conclusion that jawed vertebrates have always had fully functional spleens that are perfectly designed for their needs.

If you have the guts to read the rest, see "The Spleen, Once Regarded as Vestigial, Now Recognized as a Critically Important Organ".