I would simply say:
In identical twins, he says a group of genes that form pretty hands may combine to create a desire to decorate the hands.
I would take out the whole section: in such a way as to.
There is nothing "wrong" about that section, it just sounds too wordy.  It will roll off the tongue better if it is done simpler.
but I want to ask who is he?
That was what stood out most about this sentence. I am assuming he is already defined in the context where this sentence is being used.