"DNA doesn't prove what a species is."
"It's how humans identify what a species is."
In other words, its how humans identify that the organism is of the human species. Duh.
"DNA provides only the chemical information."
And when that chemical information matches the "blueprint" for humanity, the organism containing such information is human.
"I don't see how you can conclude that an embryo is a human being on the sole basis that it can't be anything else."
If an embryo possesses human DNA and is alive, then it must be a human being. Either all living human organisms are human beings, or you believe that humans are inherently unequal in contradiction with the Constitution.