People might say that the reason is that people are bigger and smarter but really there are several physiological reasons why humans are the dominant creatures on earth.
Mankind is smarter. We have larger brains than any other animals. Over the centuries man has added large amounts of protein to his diet. Proteins and fats build brains. The only other creature with an equivalent brain size to body mass ratio is the porpoise. (Does this mean that porpoises are self aware? Does a porpoise have purpose?).
Another physical factor is that humans are bipedal. Some of the great apes can walk on their hind legs but our pelvic structure is unique. We are meant to stand and to walk in a standing position. Plodding through the grass on all fours and running into a large predator is not a good thing. If you can stand you have a chance of seeing where the predators are.
Mankind has its eyes in the front of the head. Predators have their eyes in the front of the head. This gives improved depth perception. The coordination of the eyes, the brain and the muscles makes throwing an object accurately a task that becomes automatic.
Humans have an opposable thumb. Some of the great apes and monkeys are very close to us in this detail. This trait enables us to grasp and throw things. This ability makes up for the fact that people don't run very fast, our teeth are not good for fighting, we don't have claws and we are really not that strong when compared to the large predators. Man's advantage really includes the whole hand. We have a "pinkie" finger that completes the tasks of holding and throwing. Try grasping an object without using the pinkie to close the grip.
The last physical advantage that people possess is not very glamorous and is pretty much ignored unless there is discomfort. Man has amazing feet. The human foot is made for walking. Only sled dogs and camels come close to matching people in endurance. People can walk twenty miles or more, get a night's rest and repeat the task over and over again. Whether you believe that our ancient ancestors came from central Africa or if you believe that they came from southern Asia the question remains as to how people spread all over the earth. The answer is they walked!
Humans also have a very long childhood and adolescence. A two-year old horse is ready to race, a two-year old child, not so much. Humans spend a long time learning how to survive both individually and in groups. Sadly perhaps, scientists contend that the racial and physical differences between and among people that have meant so much to us socially and politically have only emerged in the last 150,000 years. Prejudice is a social construct.
While humans are not the strongest, the largest or the fastest of God's creatures we do possess a variety of physical assets that have allowed us to dominate the earth.