Oh, one other thing I noticed.
You know how newborn babies can't support their heads, and you have to be careful to support their heads for them when you hold them? I've always wondered about how cave babies survived, when their parents must sometimes not have realized they needed head support at all times.
Now I have my answer. Duncan can hold his own head up, at least when in a near vertical position. I noticed this when trying to burp him - it actually makes burping him harder, as when I try to flop him over my shoulder, he'll hold his head up vertically rather than flopping over as I intend.
Seems like paleo babies are not quite as fragile as neolithic babies.