Do you write humans’ or human’s?

The correct form depends on the context:

• “Humans’ “ is the possessive form used for something that belongs to or is associated with multiple humans. For example:
  • “Humans’ impact on the environment has been significant.”
• “Human’s” is the possessive form for something that belongs to a single human. For example:
  • “The human’s reaction to the news was surprising.”

So, use humans’ for something belonging to more than one human and human’s for something belonging to one person.