Dolphin can tell calf who's mum

I have read an interesting news at the BBC news site http://news.bbc.co.uk/2/hi/science/nature/7511352.stm ( written by Anna-Marie Lever
Science and Nature reporter, BBC News). This news is regarding the findings of a US team appear in the journal Marine Mammal Science by which the female bottlenose dolphins will whistle more than 10 times after giving birth so that their calf will recognise who's their mum. By producing this kind of signature whistles, it may also help to prevent the female dolphins from stealing newborns from other dolphin mothers. According to Dr Fripp, theft incidents always occur in the first day of the calf's life. Don't you think it is interesting, do you? This really shows how unique the ways mammals taking care of their young. However, what had made me dissapointed after reading the news is even an animal know how to take care of their young, why humans don't? Why do the cases like dumping the newborn child still happen in our societies? Think about that!