Charles Darwin pointed out many vestigial parts of the human body in The Descent of Man. Vestigial does not mean that the parts have no conceivable use, but rather that they are vestiges or remnants of a more functional past organ.
The coccyx was one of Darwin’s original examples. The coccyx is the “tailbone,” an extension of the spine beyond the pelvis. In fetal development, the coccyx starts out as separate bones, but as we age it fuses into a single inflexible unit, sometimes fused to the sacrum above.
The coccyx is a vestigial tail. Its development is regulated by the same genes which regulate the development of tails in primates with tails. Its development and shape is similar to that of animals with small tails such as hamsters. There is a muscle, the extensor coccygis (see the classic anatomy reference, Gray’s Anatomy), which connects the top of the coccyx to the bottom, which would flex the tail if it were not fused.
It does not make sense to view the coccyx as an intelligent design. While the coccyx has some uses, such as the attachment point for some muscles and a weight-bearing structure when we sit, it could serve without closely resembling a tail, or starting as separate bones and then fusing. Having a muscle “designed” to flex a fused, immobile bone makes no sense.
By itself, the coccyx is not a logical proof that evolution occured. It is merely evidence which makes sense within the theory of evolution, and which makes no sense in an intelligent design. Human anatomy as well as the natural world is filled with such evidence. The only way to end up with a theory of intelligent design is to start with it, and then blind yourself to the contrary evidence. That’s not science.
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