One interesting aspect is that it assumes the animal brain is great for some things but less good for logic-based flexibility. One might argue that human intelligence is animal intelligence "virtualized" by language and consciousness.

The idea is appealing but I have no idea if its true.

The title seems a bit odd, seeing as the hypothesis described seems to be describing a way that expanding brains can (or did) lead to higher intelligence. No, it isn't "just scale everything up", but it still has size as a major controlling factor.

There is good evidence that size is most things if not everything. We have big brains, hence we have more intelligence than chimps. We cook our food, so we don't spend all day feeding our big brains.

Brain size is correlated to intelligence in humans by 0.35.

Cooking food is an adaptive behavior that reduces disease and alters nutrition. It was the gradual exploitation of nature for the domestication of monocultural, industrial agriculture with supply chain processing that makes for most food modern people eat including "convenience" foods. This division of labor, whether organic farmer or pseudo-family megafarm, is what renders individual hunter-gathering a waste of time. From this over-abundance of calories and protein, it could support more robust bodies and larger brains, but it's a moot point considering obesity and the inevitability of the technological singularity.

Regarding brain size, there is a very nice TED talk:

http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_...

The speaker argues that while there are animals with brains bigger than ours, their neuron density is lower; overall, humans have the highest number of neurons. She goes on by noting that the energy that the brain consumes depends only on the number of neurons, not the size, thus making humans the species that has the most energy-hungry brain. This leads to some interesting theories on how the evolution of our brain is related to our nutrition habits, which I found quite mindblowing.

A way to test this hypothesis: elephants and certain whales have bigger brains than us. By the article's reasoning we should find mechanisms in these animals' brain which prevents neurons from "untethering".

I like your gist of putting the hypothesis to test, but there are serious practical factors that would prevent your proposed experiments. Small- and medium-sized mammals (e.g., rodents and primates, respectively) are somewhat convenient for experimenting in that they can be housed/fed humanely and fit into an fMRI machine whose aperture is ~0.5 meters in diameter. I do not see how one could reasonably do the same for elephants and whales.

But let's do a thought experiment and see if we can reasonably dispense with the need for experiment itself. The article (via the researchers' statements) zoomed past a detail: cortical surface area is much more indicative of neural processing capability than gross brain volume. In many contexts, a neuroscientist might use "brain size" as shorthand for cortical surface area. Also consider that more "advanced" mammals tend to have more convoluted cortexes, thus larger cortical surface areas. So it's quite possible for a large mammal's (whale's or elephant's) brain to be volumetrically larger than a human's, but to have relatively smaller surface area because it is less convoluted.

In the event that we could actually accomplish such a comparative study as you propose, we'd probably find that "tethering" does not monotonically increase with surface area. Then we'd determine that the authors' hypothesis is overly simplified.

For those of you comparing animal brains to human brains and how it relates to consciousness and intelligence take a look at the "Cambridge Declaration on Consciousness." (signed on July 7, 2012)

... it's just how you use it