system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do geese travel so far during migration? I understand the lack of available food during winter, but why is 5,000 miles necessary?
gpt
“Necessary” is the wrong question. It worked, and it kept working generation after generation after generation. No pressure to change.

Clarification: is your question actually about evolutionary pressure and natural selection?