So..humans & xenos are related?

I always suspected humans were in someway responsible (directly or indirectly) for the creation of the xeno, although admittedly unsure quite how. Anatomically speaking, both upright bipeds, 4 limbs, opposable thumbs, head, torso etc. Too much of a coincidence not to be even plausible. The events of Prometheus have further reinforced my theory. In laymans terms...... Shaw 'gives birth' to squiddy.... Squiddy 'impregnates' engineer..... Engineer 'gives birth' to crude early xeno.... Ergo, shaw is the xeno's grandmother? Am I missing something?