Dogs are unique in that no other mammal expresses a 100-fold size differential within its genetic base (from 2-pound Chihuahuas to 200-pound Newfoundlands).
Scientists say the causal agent is a single protein in a gene fragment that controls the size of dogs.
Genetically, the yapper arguing with your ankle is almost identical to the drooling behemoth bred to hunt bears, except for a tiny bit of DNA that suppresses the ‘insulin-like growth factor 1’ gene.Dog breeders have unwittingly been selecting for it since the last Ice Age. Dogs emerged from the wolf about 15,000 years ago, and as far back as 10,000 years ago, domesticated dogs as big as mastiffs and as small as Jack Russell terriers were trotting the earth.
So where does the gene for “small” come from? It appears to have originated with Middle Eastern wolves, and to have appeared early on in the speciation of wolves to dogs.
Suppression of the IGF-1 gene appears to be associated with a longer life span. Conversely, animals across a wide variety of species have been shown to have an increased risk of death from age-related diseases such as cancer and heart disease if higher levels of IGF-1 are present.