یک نظریه باستانی به نام "حیات گرایی" ادعا میکند که موجودات زنده بی نظیر هستند چون آکنده از مواد یا انرژی خاصی بوده که جوهر و ماهیت زندگی است. 
One ancient theory was an idea called vitalism, which claimed that living things were unique because they were filled with a special substance, or energy, that was the essence of life. 