All living organisms are the end products of billions of years of evolution. In my view, all of them are tied for being at the top.

Do you have a specific set of criteria for judging the winner? What taxonomic level are you judging (species, genus, etc)?

Intellectually human beings but dependent on self sufficient plants.

All living organisms are the end products of billions of years of evolution. In my view, all of them are tied for being at the top.

Do you have a specific set of criteria for judging the winner? What taxonomic level are you judging (species, genus, etc)?

Dear Sir, Adam B Shapiro

Thank you very much

My answer is "No"

You have to judge yourself by any thing.

Dear Subir Bandyopadhyay,

Thank you very much

Barnacles! They have the largest penis relative to their body size!

On Earth, the top species, in my humble opinion, are the plants because they make their own "food" and also make life possible for the others, not just by being "eaten, but also by releasing oxygen into the atmosphere and fixing carbon by incorporating carbon dioxide into sugar.

Dear Michael Reuscher,

Thank you very much

Dear Khaleel A Abu-Sbeih,

Thank you very much.

If you believe in evolution, it might be reasonable to conclude that the unicellular organisms are the oldest.

Dear Valentine Enyinna Anyanwu,

Thank you very much

Humans are top - top in destroying the environment and all these wonderful organisms living all around the world. 

So humans are on top, but they are a despot in the empire of the living world. All actions  are subordinated to their own advantage.

I am afraid if we would organize free elections humans would not be on top any more!

Rudolf Ritt, I really agree with you on your opinion about humans destroying the environment. I have a firm belief in what you just said.

Dear Rudolf Ritt,

Thank you very much

Dear Khaleel A Abu-Sbeih,

Thank you very much

The present representatives of any lineage are the result of long evolutionary processes, therefore they constitute in themselves the maximum exponent of an evolutionary process. Homo sapiens is the species with the greatest adaptive capacity, being the only one capable of obtaining mental abstractions. This thanks to the development of his nervous system.

But these abstractions have not only allowed him to increase his adaptive capacity to inconceivable levels, but have made him the only species that is consciously designing its extinction. Also, and unfortunately, it has dragged one of the darkest habits of hominids and rarer among mammals, and is the ability to kill specimens of their own species, the biological basis of wars.

Oceanic Plankton are the top life forms. This diverse group of creatures from single cells to a few thousand cells are the foundation of all life  on this planet. We have all descended from or been organized by this group

I fully agree with the opinions of Adam B Shapiro & Antonio López Almirall that all existing species are top creature of their own kingdom. But human may be top in their creative and destructive and egoistic powers, as well, as cited by Rudolf Ritt. Again, by thier recent technological advancement, human also knows that hunan body hosts more than 1000 trillons of microbial cells on & in its body, surpassing the mammal cells by a ratio of 1:10 in numbers, and in terms of gene numbers, the human body microbial world (microbiome) surpasses the mammalion genes by a ratio of 1:100. Now, it is also clear that the human microbiome and their metabolites can control human gene expressions and functioning, and resonsible for human health & diseases, can make life a heaven or hell. If we live a balanced life, the microbiome will be in harmony to provide us a disease-free health and life span, if not, the microbiome turns against, making life disease prone  & a hell. In this perspective, I don't see a supremacy of human anymore. It is time for we human to recognize the importance of all species, adapt to an eco-freindly harmonized life style for preserving the environment, and for better health & living.

Dear Antonio López Almirall,

Thank you very much

Dear Bob Neuweiler,

Thank you very much

Dear Tapan Kumar Mazumder,

Thank you very much

https://en.wikipedia.org/wiki/Model_organism

I agree with Dr.Ritt

A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolicand developmental pathways and genetic material over the course of evolution.

What does "top" mean?

It is always said that humans destroy nature. To this I would add the word "actual". With that I wish to emphasize that man destroys the nature that accompanies him, with that I want to emphasize that man destroys his nature. What is sadder, its nature consciously and sometimes planned. We do not understand that this destruction, although it has an obvious domino effect, will not destroy all living beings. As other times nature will recover from any event of mass extinction. An atomic war, for example, is said to survive cockroaches. The paradox of this story is that with its actions man has already begun his self-extinction, because in my view, nature as such could not be destroyed by any living organism, at least until today. As someone already said at the Earth Summit in 1992: There is a species in imminent danger of extinction, the human being.

It sounds like you are writing a term paper.  This forum is to discuss ongoing research projects, not to give you references for your classes.