The frostbite theory sounds more reasonable to me.

The evidence: maybe!!

Collard and colleagues first published their finger amputation thesis a few years ago but were criticised by other scientists, who argued that the amputation of fingers would have been catastrophic for the people involved. Men and women without fully functioning hands would be unable to cope with the harsh conditions that prevailed millennia ago.

Sounds pretty fair.

Since then, Collard, working with PhD student Brea McCauley, has gathered more data to back the amputation thesis. In a paper presented at the European Society conference, they said their latest research provided even more convincing evidence that the removal of digits to appease deities explains the hand images in the caves in France and Spain.

Oh really? Sorta interesting, okay, what's the evidence?

The team looked elsewhere for evidence of finger amputation in other societies and found more than 100 instances where it had been practised. “This practice was clearly invented independently multiple times,” they state. “And it was engaged in by some recent hunter-gatherer societies, so it is entirely possible that the groups at Gargas and the other caves engaged in the practice.”

...

That is not convincing evidence.

Sure, it's possible. If someone assembled some data that showed that in the modern day, ritual amputation is way more common quantitatively than accidental loss of digits, and showed that they were able to reject some other plausible explanations (e.g. showing that there wasn't a particularly cold climate in that area that would cause frostbite to be more common than normal), then sure. But that's not this paper, it sounds like.