The dog is the first domesticated animal, from the time when people were just hunters-gatherers and long before the emergence of agriculture, about 18,000 years ago. It is regarded as the most devoted animal to man.
The largest dogs belong to the Swiss breed Saint Bernard. The largest individual was Duke, which belonged to Dr. A. M. Bruner from Oconomowuc (US) and had 135 kg (390 pounds) (as big as an average black bear) when he died in 1965.
The smallest dogs in the world belong to the Mexican breed Chihuahua. Most of them weigh no more than 450 g (one pound) along their life and can be fed with 50 g of meat daily; but despite this, they are quite aggressive. These dogs were being drawn on the Mexican pyramids, and it seems they were worshipped. By selection, they got increasingly smaller, while their eye globe did not follow the tendency, that's why many Chihuahua have too short eyelids and cannot close their
eyes.
The record of longevity amongst dogs belongs to Adjutant, a black Labrador. It lived 37 years and 3 months (August 1936 - November 1973) and belonged to James Hawkes of Lincolnshire (England).
Big dogs are considered very old at 14 years and small ones even at 10!
Arctic dogs are able to drag sledges charged with weights over 1,200 kg (3,000 pounds). The strongest was Charlie, which on 9 January 1961, in front of numerous witnesses, dragged a sled charged with 1,425 kg (3,560 pounds) in Ancher Saint (Alaska).
Today dogs are used as pets, to guard the house and hunt.
But the Celts employed dog battalions in battle! They were put in front of the troops during the confrontation.
During the slave history of America, dogs were used to find slaves flown from the plantations, while Spaniards employed the dogs to find the Indigenous of the Americas hidden in the forests. This was possible due to the extremely acute smelling sense that dogs have. It is estimated that the dogs can distinguish about 500,000 different smells.
Just to have a picture of how developed the dog olfaction is, you should know that dogs can smell quinine even dissolved at a ratio of 1:10,000 (a gram in a cub of water) while pure quinine is inodorous for people. More than that, a dog brings back the stick thrown by its owner due to the owner's smell impregnated on the stick, not by detecting visually where the stick fell.