system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do we start flailing out arms and legs almost uncontrollably when we're free falling?
gpt
This could be due to the moro reflex. The moro reflex, also known as the startle reflex, is an instinctive human trait seen in infants. When they feel like they are falling or not being held tightly they flail their arms out to grasp and hold. It is believed to be an evolutionary trait, in that babies who grab and hold when falling survived at greater rates than those who didn't. There is some speculation that the moro reflex is a holdover trait from prehuman ancestors who lived in trees. Flailing and grasping are a good way to survive a fall when among the branches of a tree.