|MadSci Network: Evolution|
If you view evolution as progressive from the simplest organisms to more complex, at what point did the existence of a circulatory system and heart begin to be necessary. Was this related to the size of the organism? Was there a period of multicelled creatures capable of circulating their fluids without a heart? What animals today do not have circulatory systems? Jellyfish? In other words, what is the relationship between size, habitat ( aquatic or land) and the existence of a heart? I don't know whether to be looking in biology or evolution. I'd be happy for some direction.
Re: At what point in evolution was a circulatory system and heart developed?t
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