What is teat ownership?
When you have a litter of babies, one takes top left nipple, another takes top right, and never shall they switch. Biologists had hitherto thought that teat ownership reduces fighting, as everyone can have their own teat. This behavior is ubiquitous in mammals--cats, pigs, dogs, sheep... and.. binturongs.
She observed that the cubs were fastidious about their teat, and generally stuck to it. Most cubs in her sample preferred to suckle on the rear left teat, and they fiercely protected it against other cubs once they've won it. The author also weighed the cubs as they grew up, and the result justified the fuss 'round the teat.
So teat ownership is not just about reducing fighting among baby animals, it also encourages healthy competition (unless one of those babies dies) to obtain the best food. And better food means stronger, healthier baby.
Lucky for humans, we generally do not have to fight for it, unless you have a twin.
info: Growth and teat ownership in a litter of binturongs. Patricia A. Schoknecht, Zoo Biology, volume 3, issue 3, pages 273–277, 1984