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Apart from mammals and birds, most animals develop as eggs exposed to the vagaries of the outside world. This development is energetically “costly”. Going from a tiny egg to a fully functioning organism can deplete up to 60% of the energy reserves provided by a parent. In cold-blooded animals such as marine invertebrates (including sea stars and corals), fish and reptiles, and even insects, embryonic development is very sensitive to changes in the temperature of the environment.
