Common descent- explain the DIFFERENCES
So in order for common descent to separate itself from common design it needs to explain the differences. It pretends to do so with the "decent with modification" motif, but that only explains minor variations of an already existing body plan. And from observations we know that those variations oscillate- the beak of the finch is a prime example.
Yet all we know about organisms and their body plans is summed up nicely:
What makes a fly a fly? In his book (English title) “Why is a Fly not a Horse?”, the prominent Italian geneticist Giuseppe Sermonti, tells us the following:
Chapter VI “Why is a Fly not a horse?” (same as the book’s title)
”The scientist enjoys a privilege denied the theologian. To any question, even one central to his theories, he may reply “I’m sorry but I do not know.” This is the only honest answer to the question posed by the title of this chapter. We are fully aware of what makes a flower red rather than white, what it is that prevents a dwarf from growing taller, or what goes wrong in a paraplegic or a thalassemic. But the mystery of species eludes us, and we have made no progress beyond what we already have long known, namely, that a kitty is born because its mother was a she-cat that mated with a tom, and that a fly emerges as a fly larva from a fly egg.”
I would even say that common descent, as in all of life's diversity owing its collective common ancestry to some unknown population(s) of single-celled organisms, cannot be tested. To date the only "tests" we have assume coomon descent and then show what is thought to be confirming evidence. What is needed is to test that assumption. But in light of what Dr Sermonti tells us there isn't any objective way to do that.
For example the only reason we "know" that mutations can allow for upright, bipedal walking is because humans have that ability and other primates do not. And we "know" we evolved from some non-human primate. However that is about the most stupid way to present a case. But I digress.
So here is the chance for Zachriel or any other evo to ante up. The following site demonstrates the differences between humans & chimps. Take one and explain the mutations which allowed/ afforded the differences and you may be on to something scientific:
Chimps become Human?