Here's why:

* Diploid cells have two sets of chromosomes, one set from each parent. This is the typical state for most animal cells.

* Meiosis is a specialized cell division process that reduces the number of chromosomes in a diploid cell by half, resulting in haploid gametes (sperm and egg cells).

* Haploid cells (n) have only one set of chromosomes.

* Fertilization is the fusion of a haploid sperm and haploid egg, restoring the diploid state in the offspring.

Therefore, animal cells must be diploid to undergo meiosis, as this process requires the separation of homologous chromosome pairs.