Humans and the majority of animal species cannot synthesize essential amino acids (Info: Campbell biology 9th edition). However, meat, eggs, et cetera provide all required essential amino acids. And meat comes from animals.

1.Main question:

So how do these animals we eat get their essential amino acids if they cannot synthesize them either?

2.My hypothesis:

I know they can get it from their diet, but wouldn't it become a never-ending cycle of passing on essential amino acids?

3.Subquestion if hypothesis is proven:

If that is the case, where did these essential amino acids come from?

Thanks in advance!

Kind regards,


  • $\begingroup$ No david that is not the case. I think your comment is not needed at all, I was just wondering this simple fact on which I was answered. Your comment is highly bothersome as you are assuming I am stupid. I ask a question as I don't know the answer can't find literature for a definitive answer. Honestly disappointed, please be constructive or don't waste my time at all. $\endgroup$ – Jay Jul 25 '16 at 6:15
  • $\begingroup$ My comments (now removed) were made as a courtesy as I had voted your question down. They were meant to be constructive. I neither said nor implied you were stupid, but asked you not to assume Campbell was. I think you will write better questions for Biology SE if you express them clearly and then see if there isn’t an evident or easily obtainable answer. Your question, in effect, is “If humans can’t make certain essential amino acids, where do those in their diet come from?” An internet search finds, for example, a Wikipedia entry with a discussion of plant sources of essential amino acids. $\endgroup$ – David Jul 25 '16 at 8:00

Bacteria and plants are able to synthesize all amino acids, as they are capable of nitrogen fixation. If animals eat plants, they get the essential amino acids needed for their proteins. Humans get the essential amino acids by eating these animals or directly by consuming plants. So yes, it is a never-ending cycle of passing.


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