Are big dogs smarter than small dogs?

John - Dogs come in all sizes, from tiny Chihuahuas to giant Great Danes. Their head size is hugely different, as must be their brain size. Does this mean that a Great Dane is massively more intelligent than a Chihuahua?

Mel - Dogs are indeed  one of the most morphologically diverse mammals on the planet, with the smallest dogs weighing up to 17 times less than the largest dogs. This means that some dogs can have a brain twice as big as other dogs.
We put this question on the forum and twitter. Alan Calverd made the point that we also need to define intelligence in a dog. To answer this, we approached biological anthropologist Daniel Horshcler, from the University of Arizona, published a study last year that looked at brain size specifically in dogs.

Daniel - We studied over 7000 dogs from 74 different breeds, and found that breeds with larger brains do have better cognitive skills, that can help animal control their behaviour. Dogs with bigger brains have better self-control – after being forbidden from taking a treat, they were able to wait longer before giving in to the temptation of stealing it, even after controlling for their training history. Larger-brained breeds also have better short-term memory, as they were better at remembering the location of hidden food, after delays ranging from one to two and a half minutes.

Mel - Although big brained dogs were more skilled in some areas, they were not better at physical reasoning, or understanding social cues, like responding to pointing gestures.

Daniel - While it appears that differences in brain size could make larger dogs more skilled in some areas, it’s not fair to say that they are massively more intelligent than their smaller counterparts.

Mel - So what makes brains more intelligent?  I spoke to Tim Rittman, a neurologist at Cambridge University, to wrap my brain around it.

Tim - There are a number of factors that make brains more intelligent. Size helps, but it isn't everything. As the brain has developed through evolution, the most recent addition has been the frontal lobe. This handles parts of behaviour and planning, so-called executive functions.
One way to make the brain more efficient is to have folds, which is why the human brain looks so wrinkly, but a hedgehog or a mouse brain is smooth. These folds help shorten the distances between any two brain regions, making the brain more efficient. So, ultimately how intelligent your dog is depends partly on size for some brain functions, but also on balancing the cost of brain connections, or wiring, against having an efficiently organised brain.

Mel - Thanks to Tim and Daniel for their answers. Next week it’s Steve’s question about fusion.

Steve - With the advent of fusion power apparently only being 20 years away and the construction of commercial prototypes to start soon. How much do we expect to get out of this energy wise for what we put in, is it twice as much out or 1000 times as much out? And is it also true that nobody has managed to get out more than they’ve put in to date?