Final answer:
Polyploidy is a poor explanation for the increase in chromosome numbers in animals because it is rare and usually results in sterility, which hinders the ability to reproduce and pass on genetic material.
Step-by-step explanation:
Polyploidy is not a very good explanation for how animals increased the number of chromosomes they have due to its rarity and the associated sterility it causes. Polyploid animals are extremely rare, and examples can be found among flatworms, crustaceans, amphibians, fish, and lizards. These animals are usually sterile because meiosis cannot proceed normally, thus mostly producing aneuploid daughter cells that do not result in viable zygotes. Unlike plants, where polyploidy is common and can contribute to evolutionary diversity and robustness, in animals, polyploidy leads to reproductive issues and is not a common mechanism for increasing chromosome numbers. Occasionally, some polyploid animals can reproduce asexually; however, this is not a typical method for the proliferation of higher animal taxa.