Aasimars and Tieflings are derived from the Half-Elf subrace, not Human. But they are listed under Human. I guess maybe it's because there's so much under Half-Elf already, but it can be confusing.
They were changed to Human again.
edit - A great move really, they needed it IMO
I created an Aasimar character with human as the base race. I received an error message saying that the base race did not match the subrace.