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Lines of evidence: The science of evolution :

Homologies: anatomy

Individual organisms contain, within their bodies, abundant evidence of their histories. The existence of these features is best explained by evolution.

  • Several animals, including pigs, cattle, deer, and dogs have reduced, nonfunctional digits, referred to as dewclaws. The foot of the pig has lost digit 1 completely, digits 2 and 5 have been greatly reduced, and only digits 3 and 4 support the body. Evolution best explains such vestigial features. They are the remnants of ancestors with a larger number of functional digits.
Pig foot bones

  • People (and apes) have chests that are broader than they are deep, with the shoulder blades flat in back. This is because we, like apes, are descended from an ancestor who was able to suspend itself using the upper limbs. On the other hand, monkeys and other quadrupeds have a different form of locomotion. Quadrupeds have narrow, deep chests with shoulder blades on the sides.

Monkey/human chest comparison

  • Hoatzin chicks have claws on their wings, as do some chickens and ostriches. This reflects the fact that bird ancestors had clawed hands.

Claws in hoatzin chick and Archaeopteryx

Lines of Evidence
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