Why do male deer have antlers?

Answer: Competition and sexual selection

Competition and sexual selection ✓ — Correct! Sexual selection! Male deer grow antlers annually for: (1) Male competition—sparring for mates (rutting season). (2) Female attraction—larger antlers = stronger genetics. (3) Display dominance—avoid fighting through intimidation. Antlers: bone structures (shed yearly, regrow larger). Covered in velvet (blood vessels) during growth. Different from horns (permanent, keratin). Costly to grow—requires calcium, energy. Handicap principle: can afford large antlers = good genes. Usually only males (exception: caribou/reindeer females too).

Storing nutrients for winter — Wrong. Antlers don't store nutrients—they're made of bone and are shed annually. Growing antlers actually depletes calcium reserves rather than storing them.

Regulating body temperature — Wrong. Antlers don't regulate temperature—evolved for sexual selection. Males compete through antler combat for mating rights.