That and genetic data and transitional fossils and... you know. What YE creationist Dr. Wise says is "very good evidence for macroevolutionary theory. The phylogeny I showed you is based on DNA. But you can do the same thing on highly conserved molecules like cytochrome C. Here:
And all this was first noted by Linnaeus on anatomical data, hundreds of years ago. He didn't know what to make of it, but he recognized it was important:
And DNA, transitional fossils, anatomical data, cytochrome C, etc. indicates humans are mammals, but whales are not boreoeutherians. They belong to the group that includes carnivores and ungulates.
Well both of you are placental mammals, anyway. Rather distantly, but still have a common mammalian ancestor.
More closely. Humans and monkeys differ by (IIRC) three amino acids in cytochrome C.
Different phylum. Sorry.