Dunno. Something we can't know at this point really. Although I find the thought quite interesting to ponder and question, even though the subject matter is pretty gross and sad.
" The results of their study, funded by the Royal Society in England and the U.S. National Science Foundation, are detailed in the December issue of the journal The American Naturalist.
They found that several factors contributed to parents developing a taste for their own offspring.
In some cases, cannibalizing their own young puts the same evolutionary pressure on the eggs that a predator would: the faster the eggs develop, the greater their chances of survival.
Cannibalism was also found to increase the parent's reproductive rate by apparently increasing mate attractiveness, though Klug says they're unsure as to why this might be.
Some energy benefit to eating the eggs was also observed, but no one benefit alone accounted for the spread of filial cannibalism through the population.
"You can't explain filial cannibalism in all of these animals with just one benefit," Klug said.
Klug said filial cannibalism could be a way to root out offspring that take too long to mature and therefore require a little too much parental care — this strategy would conserve the parents' energy for subsequent, faster-developing batches of young.
"They initially overproduce offspring and then later remove some of the inferior offspring," Klug explained.
General competition within a species for resources may also limit parents to the amount of energy and time they can spend raising their young, so they force their eggs to grow up fast or get eaten."
Source:
http://www.foxnews.com/story/0,2933,311745,00.html