Some reflexes, like the rooting, sucking or grasping reflex, are theorized to exist because

They have survival value because reflexes are involuntary movements/actions and some reflexes occur only specific period of development .These are the some of the normal reflexes seen in the newborn babies.It helps with the newborns interaction with caregiver.

The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.