Dogs' brains are SHRINKING - and humans may be partly to blame, study warns

They may be man's best friend, but humans are at least partly to blame for dogs' brains getting smaller. 

Scientists in Hungary report that the domestic dog has a substantially smaller brain compared with its wild ancestor, the grey wolf.

Domestic dogs' brains have evolved to become smaller because pooches live in simpler environments that require less brain power compared with their wild counterparts.

While the experts argue there may be other factors leading to the size decrease in domestic dogs, they do not identify what these are exactly. 

However, in the wild, factors such as hibernation may be fueling a decrease in brain size for other species in the dog family, they say. 

Researchers wanted to see if the domesticated dog (Canis familiaris, pictured) has a uniquely small brain compared with other species in the canid family, including wolves, coyotes and jackals

Brains of domestic dogs have evolved to become smaller because they live in a simpler environment compared with their wild counterparts. Pictured, a 3D model of the dog brain based on high-resolution CT-scanning

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The study has been led by by László Zsolt Garamszegi from the Institute of Ecology and Botany, Centre for Ecological Research, Hungary.

'The dog is a canid species that was domesticated from its ancestral species the grey wolf at least 15,000 years ago,' the team say. 

'Over 400 breeds of dogs exist today, and the overall pattern is that relative brain size is dramatically reduced in dogs as compared with the ancestral species, the grey wolf.' 

The theory that dog brains have got smaller during centuries of domestication has been widely-accepted by vets and researchers alike. 

Whether it's foraging for food, avoiding predators or finding mates, domestic dogs have to deal with fewer cognitive demands compared with wild dogs. 

Due to this reduction in the need for brain power, domestic dogs' brains have gradually shrunk, the theory goes. 

The team explain: 'This phenomenon is thought to be a result of the decreased necessity for metabolically costly brain tissue in a domesticated environment.'   

Domesticated dogs show a substantial decrease in brain size compared to their wild ancestor, the grey wolf (Canis lupus, pictured)

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The researchers wanted to see if domestic dog brains were especially small (relative to their body size) when compared to their wild relatives. 

They analyzed brain and body size of 25 canid species, including the domestic dog (Canis familiaris), the the grey wolf (Canis lupus) and the common raccoon dog (Nyctereutes procyonoides). 

Domesticated dogs had a substantial decrease in brain size compared to their wild ancestor, the grey wolf, they found. 

But overall, the domestic dog had a relatively large brain size in relation to some of the other species looked at. 

Interestingly, the study found that the common raccoon dog is a 'more pronounced outlier' in terms of brain size reduction. 

In other words, the common raccoon dog's brain is unusually small for its body size – and the researchers think this is because it's the only one that hibernates.  

Pictured, the common raccoon dog (Nyctereutes procyonoides), a wild canid species that hibernates 

This graph plots the brain size (y axis) and body size (x axis) of individual canid species, including the domestic dog (Canis familiaris). Note the 'outlier', the common raccoon dog (Nyctereutes procyonoides), which has an unusually small brain for its medium-sized body

Hibernation is associated with extensive periods of low metabolic activity and food scarcity, so it likely leads to a reduction in brain size, the team say.

'Prolonged periods of food shortage, such as during hibernation, prevents the evolution of large brains due to their constantly high energy demands,' the team say.

The study concludes that while domestication does contribute to brain size reduction in dogs, hibernation is another cause too, at least for wild canids. 

Domestication, the authors say, should not be overemphasized as a 'uniquely powerful evolutionary force' that shrinks dog brains. 

The study has been published today in Biology Letters.