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Scientists
believe that all life began in the ocean, and that we are decendants
of fish. Over time animals crawled out of the ocean and developed
lungs to breath on land. Many changes have occurred in animals
since that time. Humand have body parts that they do not even
need any more, like an appendix
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During
the embryo stage many animals look alike. It is not until
they are a fetus, that you can tell them apart.
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Eventually
a human will develope a nose instead of a snout like a dog
or pig.
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An
embryo becomes a fetus when all it's organs and other
features are in place.
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The
limbs
of these vertibrates first resemble fish-like buds. The eventually
grow into arms, legs and wings
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After
becoming a fetus, animals begin to develope features that are
specific to that animal. During this time these animals begin
to excercise the muscles of their lungs by breathing in and out
amniotic fluids
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