But doesn't there have to be a fairly large amount of functional information in DNA that differentiates the macro-level body features of even closely related species? Or do you believe that essentially all DNA within a species group is essentially the same, but with some small mutations in regulatory areas that account for the difference? If so, it seems unlikely that complex macro-level differences can be accounted for by simple DNA differences.
There is an entire branch of science known as “Phylogenetics” that works with these similarities and differences in DNA.
Most species have the same set of “housekeeping” genes, that perform essential cellular functions. They are very different in widely divergent species, yet perform the same function in all species.
Humans and mice have 99% of the same genes in common. The genes themselves are about 15% different in DNA sequence, but if you find a gene in a mouse you are 99% likely to find that same gene in a human; it will just be 85% different.
Humans and chimps have well over 99% of the same genes in common. The genes themselves are only about 2% different.