Perhaps proof is a strong word. Sports are very powerful evidence in support of the theory that our species has evolved to survive primarily by hunting for food.
Think about the way most of our sports are played. Baseball, football (football), soccer (football), hockey (ice and field), basketball, tennis and lacrosse to name a few all involve tracking a fast-moving playing object (ball or puck) with the eyes to chase down and catch or strike, much like our ancestors tracked down prey of various sizes. Some involve various forms of struggle to gain control over the playing object which adds another twist mimicking the competition between hunters. All this activity simulates the activity of hunting for prey. Throwing demonstrates from the quintessential human adaptation of hunting with arm-flung projectiles. Anyone who has ever played sports knows the deep seated drive to chase after any moving ball – it’s pure instinct.
Compare our sports to other members of the animal kingdom. The only obvious examples of similar, chase-the-ball type of play are our two most common pets – dogs and cats. Both are obligate carnivores whose primary method of obtaining food is hunting. The instinct we share is obvious if you’ve ever picked up a ball near a loose dog or dangled a string near a cat. It is hard to think of another animal that plays in a similar fashion, but you can see hunting roots of certain dolphin behavior. See how this dolphin artfully plays with rings of bubbles. I do not know whether the dolphin was trained to do that, but it appears to be having fun independent of human interference, as does this dolphin playing with a ball.
Contrast these carnivores to the apathetic reactions of these baby elephants to a soccer ball. Witness this playful demonstration of skillful manipulation by a young pachyderm. Notice how unlike hunting this behavior is. They treat the ball like an animal might treat an inanimate piece of fruit, say a coconut. Strike or bite it until you are satisfied that it is inedible then ignore. Witness also, fully grown animals playing an actual game of soccer. Notice the riders guiding their mounts to the ball and proper position. The point to be gained from this comparison is that nobody has to train a dog to chase a ball. Retrieving, of course, is another matter entirely.
Elephants and other large herbivores have contests of dominance with each other and I have to include this one of hunters freeing two bucks with their antlers entangled). Parrots can be trained to play with balls and bicycles, but only predatory birds can be trained to track down and tackle flying objects. I’ve never had a pet rabbit, but I can imagine how a rabbit would react to a ball – with complete indifference. The same goes for gerbils and other rodents. Basically, if herbivores developed intelligence and developed an Olympic style contest, unlikely if you read gnolls, you would expect to see sports involving one-on-one team battles, racing games and probably some unexpected sports that we would never think of, but few, if any, sports with surrogate prey like a soccer ball or hockey puck. Just imagine what sport a herding animal like sheep might develop. There is almost no pressure on herding animals to develop high-IQ individuals, but what if some DNA experimenter created some intelligent sheep and they started playing sports? Perhaps they would play team sports whereby the team navigates a course in the tightest formation. Maybe jumping games would develop. I just could not see sheep manipulating a prey-like object. Of course, sheep don’t use tools at all. Why would they? They are not hunters.
Sports are driven by instinct. Humans are imbued with hunting instincts. Our eyes are positioned in the front of the head to enable 3-dimensional tracking of moving objects, like most predatory animals. We have an instinct to chase to acquire food. Watching players chase a soccer ball along the field, you could easily imagine them chasing an animal in a similar manner. We have abandoned hunting as the main source of food, but our evolved instincts remain as evidenced by the thrill of chasing down a fly ball or a tennis serve. Think about this the next time that you hear someone spout some nonsense about evolution and vegetarianism.