And exactly how can you, by empirical scientific means, prove an absence of purpose? The existence of purpose or non-existence of purpose is an a priori assertion, a belief. Especially if the purposiveness were an immensely complex phenomenon that, until enough data could be assembled and analyzed as to prove its existence, might seem to be absent.
Just what sort of empirical measurements and experiments do you design to prove the absence of purpose? What is purpose, anyway? Seems to me to be a rather philosophical concept. Before we can decide on its presence or absence, we might actually have to have some philosophical discussion of its meaning. I'm sure you had a meaning in mind, but is that meaning scientifically provable or is it also part of the philosophical assumptions you bring to bear on the subject.