Final answer:
The descent system that includes individuals from both the mother's and father's sides is known as bilateral descent, which is common in modernized nations like the United States.
Step-by-step explanation:
The descent system that includes individuals from both the mother and father's line of descent is called bilateral descent. This system is distinct from unilineal descent systems, which trace lineage through only one parent's line. Patrilineal descent traces through the father's line only, while matrilineal descent traces through the mother's line only. In contrast, bilateral descent accounts for kinship through both parents' lines, making it the most inclusive of the descent systems mentioned.
In societies that practice bilateral descent, a person's family is composed of relatives from both the maternal and paternal sides. This pattern is common in modernized nations, including the United States, where both paternal and maternal ancestors are considered part of one's family heritage.