The number of genes in the genome of a species generally determines the complexity of that organism. Yeast has about 6000 genes, worms have about 19,000 genes, rice has about 35,000 genes. Humans have only about 24,000 genes! Human genes can be modified in more ways which is why we appear in reality to be more ‘complex’.
(The Great Courses – Understanding Genetics: DNA, Genes, and Their Real-World Application)