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Subdisciplines of biology
- Cell Biology
- Molecular Biology
Evolution as the uniting theory of biology
The Theory of evolution unites modern biology in the way that many things, such as homology (similarity between structures that is due to their shared ancestry) would not make sense without a theory of evolution and common decent. Biological evolution explains these similar characteristics as being inherited from a common ancestor. The pattern of limb bones (pentadactyl limb) is an example of such homologous structures. The fossil record shows that the pentadactyl limb originated in primitive tetrapods in the Devonian Period. Predecessors, with more than five fingers, can be traced back even earlier to the fins of certain fossil fishes from which the first amphibians are thought to have evolved. It is still found in all classes of tetrapods (i.e. from amphibians to mammals) today.
Evolution explains Vestigial structures as once having had a function. As an example, with mole rats living underground the eyes on a mole rat got smaller over time and eventually a layer of skin began to cover them which eventually led to the form they are in today. Humans and other animals also bear some vestigial behaviors and reflexes. For example, the formation of goose bumps in humans under stress is a vestigial reflex; its purpose in human evolutionary ancestors was to raise the body's hair, making the ancestor appear larger and scaring off predators. Raising the hair is also used to trap an extra layer of air, keeping an animal warm. This reflex formation of goosebumps when cold is not vestigial in humans, but the reflex to form them under stress is. However these vestigial structures and behaviors are explained by evolution in the way that they once served a purpose but no longer serve a purpose in the new environment so they have become smaller and will eventually disappear.