A Very Determined Ape

A member of our species' closest relatives gave birth at the age of 42.  Ginger the chimpanzee just had her fifth at Chimp Haven, a chimpanzee retirement home. 
I would not classify this as extremely bizarre news. After all, chimps are our closest relative as stated above, and it is becoming more common for humans to give birth well into their 40s.   For me, the intersting news is that it appears the father of the new chimp is Conan, who has a reputation for being a "ladies ape", and has had three vasectomies!
It seems you can't keep a randy ape...er, down.   I was curious about why these procedures were not successful.  In humans, the procedure is very effective though I do not have percentages at hand.  It could be some physiological difference that makes the procedure less likely to be successful or at least less likely permanent in chimps. 
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