Grief Signals to Others That We're No Longer Capable

The way we survived as human beings was to bond, build affiliations. Anything that threatens our connection with attachment figures over the course of human development would lead to increased vulnerability. Our tribal status would be diminished. And it would require extensive periods of adaptation before we could confidently reenter the social realm and participate in all the hunting and gathering or all that. So there's an evolutionary function of grieving.