All mammals share a similar structure of the vertebrae in common. For instance, in spite of its height, the giraffe has the very same number of neck bones (seven) as a giant whale and a tiny human being. How does this show evidence of a common ancestor?
The Correct Answer and Explanation is:
The fact that all mammals, including giraffes, whales, and humans, have the same number of neck bones (seven cervical vertebrae) provides strong evidence of a common ancestor. This similarity in structure, despite differences in size, shape, and function, suggests that mammals inherited this trait from a shared evolutionary origin.
Explanation
One of the most compelling pieces of evidence for evolution and common ancestry is the presence of homologous structures. These are physical features that are similar in form or position but may serve different functions across different species. The structure of the vertebral column in mammals is a clear example. All mammals, from the tallest land animal (the giraffe) to the largest marine animal (the whale) to humans, possess exactly seven cervical vertebrae in their necks.
This is not because seven vertebrae are the only number that could work. In fact, having more or fewer might be beneficial in certain contexts. However, the consistency of this number across the entire class of mammals suggests that it was present in a common ancestor from which all modern mammals descended. Over time, natural selection shaped the size and function of these vertebrae differently in various lineages. In giraffes, the vertebrae are greatly elongated to form a long neck. In whales, they are shortened and fused in some species to support streamlined movement through water. In humans, the neck supports the head and allows for mobility and balance.
This pattern of shared structures with modifications is exactly what we would expect if all mammals evolved from a common ancestor. It shows that rather than evolving completely new structures for new functions, evolution often works with existing structures, tweaking and adapting them over time. This is a powerful indicator that the diverse forms of mammals are variations on a shared evolutionary blueprint.
