One user initiated a closing vote to this question: What are some of the earliest known species on earth that display pecking order?
One user explained that my question is "homework", because "a question that addresses a basic biology concept that may seem trivial to biology professionals".
After a few friendly conversation, that user explicitly admitted that, (as a biology professional,) he does not have full knowledge of some of the foundation works in "pecking order". There is of course nothing wrong with that because no one has the full knowledge on any non-trivial topics. I truly appreciate him for bringing up an unique view-point from a biologist, which is not entire same as other biologists.
I further clarified this is not a homework question. I also explained why the question is asked. Though the question is still closed because of "homework".
If by any chance I could get any help, I will be much appreciated.