Describe one major cost and one adaptive benefit of human speech.

(Answers will vary.) The human brain is very large and energetically expensive, so the underlying neural mechanisms required for speech are very costly. In addition, language facilitates the transmission of misinformation from manipulative senders.
However, human speech provides numerous adaptive benefits, such as: facilitating social group formation, enabling "verbal courtship" to choose mates with exceptional language skills, enabling food acquisition and sharing, improving the production of stone tools, and transmitting useful information to kin and non-kin.