When you look at a kangaroo or a wallaby, it’s obvious the animal is well built for bouncing around the outback. What may be less obvious is that its arms are built for fighting—if it’s male, that is. Males of these species have disproportionately long arm bones. And the more brawling a species does, the more exaggerated the difference between the beefy-armed males and their normal-limbed mates.
To understand this evolutionary quirk, we’ll need to review the rules of fighting in wallabies