Many insects, fish, and mammals release certain chemical messengers to signal reproductive readiness. what are these messengers called?

Based on anatomical similarities, to which modern animal is dr. digger’s creature most closely related?

Which of the following best describes the expensive tissue hypothesis? brains require more energy, so the gut had to be reduced, and larger brains and tool use led to higher quality diets. increasing body size means that homo neanderthalensis had to include more fat in its diet. brains require more energy, so the gut had to be reduced as brains got bigger. brains require more fat, so the gastrointestinal viscera (gut) had to expand, and hands were needed to acquire more food.

This is a biological reaction due to a stimulus. i need this quickly !