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Okay, I'll pose my question to you too, since you seem to be pretty knowledgeable. Why would the mental arms race confine itself only to humans? It seems like other highly social animals (wolves specifically come to mind) would reap huge benefits from being a little smarter than their peers. Like I told Alter Kaker, I'm not trying to argue, I really don't get it.

As is often the case with questions about evolution, it's amazing how often Darwin himself had enough foresight to conceive of the question and suggest possible answers, way back in the 1800's, long before the anyone even knew that DNA existed, and when the fields of paleontology, geology, etc. were in their infancies:

But every one who admits the principle of evolution, must see that the mental powers of the higher animals, which are the same in kind with those of man, though so different in degree, are capable of advancement. Thus the interval between the mental powers of one of the higher apes and of a fish, or between those of an ant and scale-insect, is immense; yet their development does not offer any special difficulty; for with our domesticated animals, the mental faculties are certainly variable, and the variations are inherited. No one doubts that they are of the utmost importance to animals in a state of nature. Therefore the conditions are favourable for their development through natural selection. The same conclusion may be extended to man; the intellect must have been all-important to him, even at a very remote period, as enabling him to invent and use language, to make weapons, tools, traps, etc., whereby with the aid of his social habits, he long ago became the most dominant of all living creatures.
A great stride in the development of the intellect will have followed, as soon as the half-art and half-instinct of language came into use; for the continued use of language will have reacted on the brain and produced an inherited effect; and this again will have reacted on the improvement of language. As Mr. Chauncey Wright (1. 'On the Limits of Natural Selection,' in the 'North American Review,' Oct. 1870, p. 295.) has well remarked, the largeness of the brain in man relatively to his body, compared with the lower animals, may be attributed in chief part to the early use of some simple form of language,--that wonderful engine which affixes signs to all sorts of objects and qualities, and excites trains of thought which would never arise from the mere impression of the senses, or if they did arise could not be followed out. The higher intellectual powers of man, such as those of ratiocination, abstraction, self- consciousness, etc., probably follow from the continued improvement and exercise of the other mental faculties.
-- Charles Darwin, "The Descent of Man", 1871

Elsewhere in "The Descent of Man", Darwin writes of the obvious connection between language and complex society, since as I mentioned in an earlier post, you can't have one without the other. So his view was similar to that of the authors of the current study -- that at some point the development of a sufficiently complex degree of language/culture, there was a "snowball effect" (like a snowball rolling downhill and growing in size and momentum), where each stepwise advance opened the door to even greater survival advantage, and drove even further advances.

These type of "tipping points" are reasonably common in evolution -- once a species begins to "specialize" in a particular trait to a certain degree, it can hit a point where its success in that area increases selection pressures for even greater successes, evolutionarily. For example, the success of a predator cat depends on applying many factors to the hunt, like stealth, brains, cooperation, speed, strength, etc. But if a species of cat begins to succeed primarily through a moderate advantage in speed, evolutionary pressures will likely accelerate its specialization in its speed advantage, often abandoning most other strategies in order to extend the speed advantage to the point where the other factors become of minor importance in comparison, resulting in for example the Cheetah, which can chase down prey at 70mph. Once its ancestors began succeeding more through speed than through other methods, evolutionary selection would kick into high-gear on increasing their speed even further, relative to improvements on their already secondary attributes (stealth, etc.).

Finally, often a species will achieve a functional "breakthrough", which makes many more advancements now possible to evolve. For example, in reptiles the jaw is hinged at the very back of the jawbone (which in reptiles consists of a few different bones fused together), and incidentally is also instrumental in the resonance and function of their ears. In the descendants of reptiles which eventually became mammals, however, the hinge-point of the jaw migrated to a more forward location, leaving the rearmost components of the multi-bone jaw performing only the hearing-assist functions, instead of the dual hearing/hinge function of the reptilian jaw.

This alone was a relatively minor change, and just helped the early mammals articulate their jaws in a somewhat more flexible manner. HOWEVER, this change had a fortuitous side effect, which is that once the rearmost bones in the jaw no longer had to continue to work as the jaw hinge, they were "free" to evolve into greater specialization as resonators in the improvement of hearing. And thus they rapidly (relatively speaking) separated from the jaw and evolved into the three inner-ear bones of the specialized mammalian ear, better known as the Hammer, the Anvil, and the Stirrup. One seeminginly inconsequential change (the shift in the jaw-attachment point) happened to "open the door" to a sequence of evolutionary changes which dramatically improved the function of the early mammal's hearing -- and that of its descendants, including us.

And *yes*, there *are* transitional fossils showing the steps in this evolutionary progression, along with DNA sequence evidence of the change itself, and its evolutionary origin.

Similarly, early man may have achieved some seemingly inconsequential evolutionary change (perhaps biochemical, or structural, or in neuron functionality, or whatever), which by our good fortune happened to set the stage for the rest of our great leap forward in mental ability, making the rest possible. And once possible, made evolution able to achieve it by subsequent accumlated changes.

The full human and chimp genomes have now been sequenced, and a huge amount of research is being done on the differences (and similarities) between them. There are dozens of ways that evolutionary histories can be extracted from DNA comparisons (see for example these former posts of mine: 1, 2), and within the next decade most of the exact sequence of evolutionary changes between man and the other apes will be brought to light. Then we'll finally understand exactly which changes, and when, mankind underwent on our journey from our non-human ancestors, and how those changes brought us to where we are today.

...and even then the die-hard creationists will keep chiming in to assert, "there ain't no evidence at all for evolution, none!"