Humans are classified as Apes.
Apes don't have tails.
Except when they do.
We used to have tails. I don't mean "we" as a species; I mean you and I as individuals. We all had tails.
Embryologists divide the development of a human embryo into 23 "Carnegie Stages" based on multiple physical features. Stage 23 corresponds roughly to day 56.
From stage 14 - roughly day 32 - the embryo has approximately 12 tail vertebrae which extend beyond the anus and legs, accounting for more than 10% of its total length. The tail of the human embryo is a complex structure. Apart from 12 vertebrae it has a secondary neural tube (spinal cord), a notochord, mesenchyme, and tail gut.
By the eighth week of gestation a process known as apoptosis or cell-death has eliminated the sixth to the twelfth vertebrae as well as the other tissues. The dead cells are consumed by white blood cells known as macrophages. The remaining vertebrates also reduce and fuse together to form the coccyx.
Patrick Foye of the New Jersey Medical School reports that the construction of the coccyx is variable and often consists of anything from three to five bony segments.
Sometimes the signal to dismantle the embryo's tail fails to be activated resulting in around 100 examples of humans being born with atavistic tails.
Less than a third of these are poorly developed "pseudo-tails", but others contain muscle, blood vessels and nerve fibres. They are covered by normal skin with hair follicles, sweat glands, and sebaceous glands. They vary from about one to over 5 inches in length. A few - as in this x-ray of a six year old girl also contain some of the tail vertebrae.
This example from evolutionary developmental biology poses a difficult challenge for creationists. Why would the human embryo go through a stage of growing a complex tail only to reabsorb it? When babies are born with complete working tails where did that genetic information come from?
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