Elephants and whales have larger brains than even our brainiest Einsteins - with more neurons and interconnects, yet the typical human is vastly more intelligent than any animal.

Yes, because brain size does not equal neuron count; there are scaling laws at play, and not in the whales'/elephants' favor.

Yes. - When I said 'large', I was talking about size in neurons, not physical size. Physical size, within bounds, is mostly irrelevant. (although it does effect latency of course).

On neurons, whales and elephants are much inferior to humans.

No - they really do have more neurons, ~257 billion in the elephant's case. 1 (2014)

Since it's neurons which compute, and not brain volume, the biological aspect is just fine; we would not expect a smaller number of neurons spread over a larger area (so, slower) to be smarter...

According to google, an elephant brain is about 5kg vs a human's 1.4kg. So we have 51 billion neurons per kg for the elephant vs 75 to 60 per kg for the human. This is by the way, a smaller difference than I would have expected.

The elephant's brain has a larger cerebellum than us but smaller cortex: about 5 billion neurons vs our 15 billion ish. Interestingly the elephant cortex is also sparser while its cerebellum is denser, perhaps suggesting that we should look at more parameters, such as synapse density as well (because of course there are many tradeoffs in neural micro-circuits).

Anyway the human cortex's 3x neuron count is a theory for our greater intelligence. But this by itself is insufficient:

• the elephant interacts with the world mainly through its trunk which is cerebellum controlled
• humans/primates use up a large chunk of their cortex for vision, the elephant much less so
• humans rely far more on their cortex for motor control, such that humans completely lacking a cerebellum are largely functional

Now - is having a larger cortex better for general intelligence than a larger cerebellum? - most likely. It appears to be a better hardware platform for unsupervised learning.

But again the key to intelligence is software - we are smart because of our ability to accumulate mental programs , exchange them, and pass them on to later generations. Our brain is unique mainly in that it was the first general platform for language, not because our brains are larger or have some special secret circuit sauce. (which wouldn't make sense anyway - humans are recent and breed slowly; the key low level circuit developments were already made many millions of years back in faster breeding ancestor lineages)

Cite for the 200b and 100b neuron claims? See above for elephant neuron counts.

For humans I was probably just using wikipedia or this page based on older research.