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Anatomy (1 of 2)
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.
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.
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Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.