Some would say that the crowning feature of human intelligence is language; which, as something that all races of humanity have achieved, is deserving of such stature. Others might point to more specific features of our advanced culture to support the assertion that mankind is intelligent. Either way, it is generally considered a fact that humans are intrinsically intelligent, with certain specific exceptions.
The Boskop, a prehistoric variation of anatomically modern humans (who lived 30,000 to 10,000 years ago) so named for the small South African town their fossils were found in, possessed a skull that boasts a gargantuan cranial capacity, 40-50% larger than our own. According to neuroscientists Gary Lynch and Richard Granger (authors of Big Brain, The Origins and Future of Human Intelligence), the Boskop sported an enlarged brain and therefore an increased intelligence. In their book, they assert that the Boskop were in fact more intelligent than modern humans, though there is some criticism of this position. As only fragments of different Boskop skulls have been found, only estimates of their actual cranial capacity are available. It is said that they had between 1700-2000cc of cranial space, whereas living humans have a cranial capacity of between 950-1800cc with the average at 1400cc.
It could be said that where brains are concerned, size does matter, but only to a point. Elephants and dolphins have larger brains than humans (to name only two of the vast array of animals that elicit brain envy), but it couldn’t be said that they possess greater intelligence, and the difference is subtle. It turns out that measuring brain size is only one part of the equation. In fact, it’s the ratio between brain size and body weight that matters most. Elephant’s posses on average a brain volume of 7500g (whereas humans are right around 1500g), but when compared to their body size, an elephant’s brain is no larger than .15% of their body weight. In humans (homo-sapiens) our brains are 2.10% of our average body weight.
One of the reasons that larger animals require larger brains is that they have more nerve connections in the brain, which relates to larger regions dedicated to sensory perception. The main difference between humans and other animals is that our brains have a larger cerebral cortex, which apparently relates directly to increased intelligence. The Boskop’s, with their larger brains (approximately 4% of their body weight), had the largest cerebral cortex among hominids. As a result, some scientists are of the opinion that the Boskop were likely more intelligent than living modern humans. Besides this circumstantial evidence there is little known about the culture or language abilities of the Boskop, though Lynch and Granger have speculated that the Boskop possessed higher reasoning and complex language, but they offer no explanation for why the Boskop died out. When it is thought that our inherent intelligence is the one feature of modern humans that was most responsible for our proliferation, it seems counterintuitive that the Boskop did not enjoy the same survival advantage as us.
In any event, when the Boskop Man was discovered in 1913 and presented to Frederick William FitzSimons, the then director of the Port Elizabeth Museum in South Africa, it was first “described [as] perhaps allied to the Neanderthal but without the large supra-orbital ridges.” Since that time there has been much speculation and conjecture about the origins and meaning of the fragments. The Boskop Man (a term that is no longer used in paleontological circles) is largely regarded as an aberration, but Lynch and Granger are unwavering in their interpretation. They are confident that the Boskop were endowed with much larger brains than modern humans, and are taken with the mystery behind their disappearance.
 Brain Size Lecture, http://www1.appstate.edu/~bacharachvr/brainsize.htm
 It’s interesting to note that mice brains are on average 3.2% of their body weight, although they lack a particularly large cerebral cortex.