This is not a quote from Kropotkin. It would actually be the opposite of his writings, as he spent a whole book about how mutual aid was found in nature and was a contributing factor in the evolution of species.
In his book, Mutual Aid, a Factor of Evolution, exposes how mutual aid is present in many different ecosystems, both among same species as well as inter species. He also does some anthropological research to understand how mutual aid factors in primitive societies.
So, this quote not only is wrong as it was never said by Kropotkin, but it goes against his contributions in science (and anarchist theory).