Almost all mammals have seven cervical vertebrae. There is a fitness disadvantage to mammals that have a different number of cervical vertebrae; for example, in humans, fetuses with an abnormal number of cervical vertebrae are often stillborn, and such children are more prone to pediatric cancers. This is an example of

A) convergent evolution.
B) phenotypic plasticity.
C) constraining evolution.
D) pleiotropy

Cervical Vertebrae

The vertebrae located in the neck region of the spine, distinct for their small size and the presence of foramina in the transverse processes for the passage of blood vessels.

Pediatric Cancers

Cancers that occur in children, encompassing a range of different types of cancer that can affect various parts of the body.

Convergent Evolution

The process by which unrelated or distantly related organisms evolve similar traits independently, often due to similar environmental pressures.