Step 1: Understanding the concept of cooperation.
The passage states that language is essential in promoting human cooperation, making it possible for people to work together effectively.
Step 2: Role of language in cooperation.
Language enables communication, allowing individuals to share ideas, plans, and needs. This shared understanding promotes collaboration and makes it easier for people to cooperate toward common goals, whether in small groups or large societies.
Step 3: Conclusion.
Thus, language helps promote human cooperation by enabling effective communication, which is the foundation for working together.
Final Answer: \[ \boxed{\text{Language promotes human cooperation by enabling effective communication, allowing people to understand and work with each other toward common goals.}} \]