This is very interesting, and bring together two of my great interests in life: Vikings and reindeer, and the eternal battle between them. It seems that the reindeer, having got tired of being speared by Vikings, got together with their reindeer mathematicians and came up with this strategy to defeat the tough axe-wielding guys, with the helmets with no horns, carrying big spears:
https://www.livescience.com/64778-vikings-reindeer-cyclone.html?utm_source=ls-newsletter&utm_medium=email&utm_campaign=20190215-ls
“Vikings hunting reindeer in Norway were once confounded by "reindeer cyclones"; a threatened herd would literally run circles around the fierce hunters, making it nearly impossible to target a single animal. Filmmakers recently captured incredible aerial footage of one of these reindeer cyclones, which aired Feb. 13 on PBS in the documentary Wild Way of the Vikings, a program about Vikings and the wilderness they inhabited around A.D. 1000. One of the documentary's most striking scenes shows a re-enactment of a Viking hunt interspersed with real footage of reindeer herds. Reindeer were important to the Vikings for their meat, hides, antlers and bones, according to the film. Vikings hunting reindeer in Norway were once confounded by "reindeer cyclones"; a threatened herd would literally run circles around the fierce hunters, making it nearly impossible to target a single animal. Filmmakers recently captured incredible aerial footage of one of these reindeer cyclones, which aired Feb. 13 on PBS in the documentary Wild Way of the Vikings, a program about Vikings and the wilderness they inhabited around A.D. 1000.
One of the documentary's most striking scenes shows a re-enactment of a Viking hunt interspersed with real footage of reindeer herds. Reindeer were important to the Vikings for their meat, hides, antlers and bones, according to the film. In the cyclone scene, a lone hunter (an actor playing a Viking) approaches the herd; he notches and releases an arrow. The footage that follows shows an actual herd of reindeer running in circles. As the swirling mass of bodies thunders along a circular path, an overhead camera reveals that the herd's momentum follows a spiral shape, drawing tightly toward the cyclone's "eye" at the center. Faced with this spinning reindeer stampede, any predator — wolf, bear or human — would have a very tough time targeting and overpowering a single reindeer, making this a formidable defense strategy, according to a statement from PBS. This behavior is also practiced by reindeer kept in corrals, occurring in groups of at least 20 to 25 animals, researchers wrote in a 2002 study published in the journal Rangifer. Penned reindeer formed "cyclones" and were observed to run "invariably" in a counterclockwise direction, the scientists reported.”
The issue here is how did such a behaviour evolve in the first place? We are to suppose, according to neo-Darwinian evolutionary theory, that some random mutation arose which in an individual would lead to this group behaviour. No doubt, the behaviour once it arose, would be favoured by natural selection, but the problem is to explain how it originated in the first place.