I've been lurking for a while but only just registered, sorry if this post seems a little late.
Just a quick note on an issue raised earlier about how lungs came about. I suggest anyone interested looks into the insect respiratory system. In it's most basic form it consists of hollow tubes through the insect, and air diffuses through. Then the more complitcated / bigger insects have small are sacs that "pump" the air through (for example when an insect beats its wings). It is not difficult to see how this pump system can evolve into rudimentary lungs passing the air into tubes, and then into a separated circulatory system. I'm not saying that necessarily is the way it happened, but it certainly would seem possible and plausible for lungs to evolve, as there are steps to go through.
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