When Google launched Penguin 4.0 some folks speculated that it was using some sort of machine learning (or RankBrain) to get better by itself. I mean, it sounds nice and all but no where in Google's announcement did it mention machine learning - and trust me - Google wants to use ML in their marketing and PR as much as possible.
Well, Google's Gary Illyes told Jennifer Slegg that Google is not using Machine Learning in Penguin. This was via a simple Twitter exchange where Jennifer asked "Is Penguin a machine learning algorithm, or use any kind of supervised or unsupervised learning?" Gary Illyes responded, in short, "nope."
@jenstar nope— Gary Illyes (@methode) October 10, 2016
I believe Rand Fishkin was one of the first to speculate that Penguin using ML:
Most important detail of the announcement is the change to how it operates (ML-based consideration of ranking signals, more like RankBrain) pic.twitter.com/eA1Lo37A14— Rand Fishkin (@randfish) September 23, 2016
But this is not true - I mean, if you believe Google - which I do.
Former Google spam fighter, Murat Yatagan, said Google does use machine learning to fight spam but you need to read the whole thing to get the context.
Forum discussion at Twitter.