Vestiges are structures, anatomical configurations that has lost or nearly lost its primary function. If it has any current function, it is either a persisting secondary function, or a function gained sometime after the loss of primary one. This process is called exaptation or co-opting.
Examples of vestiges are plenty.
The middle ear bones of mammals are derived from former jaw-bones (Shubin 2007).
Early tetrapod limbs were modified from lobe-fins and probably functioned in pushing through aquatic vegetation; at some point, they became sufficiently modified to allow movement on to land (Shubin et al. 2006).
The vestigial hind limbs of boid snakes are now used in mating (Hall 2003).
But the most impressive of all, my personal favourite, is evolution of gonads –a gonad is an organ that produces gametes; a testis or ovary-.
The gonads of sharks, other fish, and even humans develop in same place, the chest. This works well for sharks, since they stay there, but in human males, as the embryo grows the gonads need to travel all the way down into the scrotum to keep cool. This causes an unnecessary looping of the spermatic cord, which causes a weakness in the body wall, leaving them prone to developing a hernia (Shubin, 2009). This is consistent with descend with modification from an ancestor we share with modern fish.
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There is mountain of strong evidence for evolution, and each day research laboratories around the world conduce more. At the same time the case for designer god is weakening.
The next question to ask is if it wasn’t design what is god for?
Original Scientific American article by Neil H. Shubin (PDF):