Because that's what humans wanted to have in a particular breed of cow, for the purpose of a) more power to pull carts as a draft animal, or b) more meat to eat from one animal.
Humans do genetic manipulation technique on animals and plants called selective breeding. Draft horses were created through mostly selective breeding. People needed large strong horses to pull heavy weights and work the land. To create a draft horse people would have found the largest and strangest specimens they could find and breed them together hoping for a foal that combined the best of each parents genetics. This type of breeding continued until the people had a fixed type. Once that happened they began creating separate and unique breeds of draft horses.
Domesticated turkeys are generally unable to fly due to selective breeding for increased chest muscle mass. This additional muscle weight makes them too heavy to be able to fly.
The heavy muscles are for grabbing onto and holding down prey for feeding purposes.
The modern horse is the result of selective breeding for thousands of years. Medieval horses were prized for their strength not speed. They were big and heavy and most likely would not be able to keep up with the present day Thoroughbred.
Depends on your body type (Heavy boned and muscled or not) but you would seem to be over weight
Heavy Heavy Low Low was created in 2004.
Xiangyang Zou has written: 'Selective removal of inorganic fine solids, heavy metals and sulfur from bitumen/heavy oils'
Heavy as a Really Heavy Thing was created on 1995-04-04.
Heavy Barrel was created in 1987.
Heavy Liquid was created in 2005.
Heavy Meadow was created in 2010.
Heavy Mental was created in 1998.