For some reason, only one ape species ever has non-small breasts. You never get large breasted gorillas, chimpanzees or bonobos even though they share 98% of their DNA with us. What is it about humans that means that that trait was evolutionarily advantageous? It's obviously a feature with significant disadvantages, so what is the advantage that offsets that for humans in a way that it doesn't for other great apes?