Along with that little fact, is the corresponding fact that none of the "higher" animals - again, not including the human animal - exhibit speech, or have a formal language, and even if you suggest that apes do, or elephants do, or dolphins do, NONE of them exhibits the ultimate in having a formal language, which is the ability to write and read books.
Thus, only humans have speech and can write books (and diaries, emails, blogs, and/or scratch on stone tablets and pass them around to others), AND, only humans have a built-in "agency" which inhibits their sexual drive.
Therefore, the acquisition of speech, formal language and writing, only developed in humans BECAUSE of the somewhat arbitrary add-on to his nervous system inhibiting his, otherwise, unrestrained sexual drive, first appearing instinctually, and later hormonally, and even later intellectually. No longer - and NOT for a very long time - has man been able to satisfy his every wish/desire/need in that area, while at the very same time, his power of speech, use of language and production of written materials has increased exponentially. (Less sex, More talk.)
Apes, elephants, dolphins, and all the other uncivilized populations wherever they may be found, have nothing to say on any topic put before them, because their sexual drive is totally unrestrained... and as a consequence, their higher-order "talking parts" never got the highly-charged kick-start (and so... there is no "thinking about it").
Humans, civilized and city-fied, have everything to say on every topic put before them, because their sexual drive is totally restrained... and as a consequence, their higher-order "talking parts" DID GET the highly-charged kick-start (and so... there is an over-abundance of "thinking about it").
Yes, Virginia... there is a direct, observable correlation between sex energy and thought. Sex energy builds up in the nervous system mechanically, automatically, simply as a result of eating and breathing and walking around, and it usually goes into ordinary, physical sex. It is also possible to push that energy higher up in the nervous system to be used for other activities. More on this can be found here.
A non-verifiable proof follows: When was the last time you had a really "enlightening", "consciousness-expanding", "mind-blowing" thought? (NOT one that you read by Rilke, or Ramana, or Rosanne Rosannadanna, and riffed-on-and-on about... but one YOU had on your own.) [Insert thought-response here]
Notice: Anybody, anywhere, can arrange their life in such a way, and coordinate their body parts in such a way, so as to locate a book somewhere, filled with somebody else's "enlightening thoughts" (B.F.D.) But, you can't so easily - if at all... okay, never - make such a well thought-out plan, and set up the circumstances of your life in just such a way, that it will reliably result in having one of your own really enlightening, "consciousness-expanding", "mind-blowing" thoughts. [Insert personal verification here]
Sex and the city, folks.
Sex and the city.
The more restrained your sexual energy - and today, it is the MOST restrained it has ever been in the longish history of mankind on this planet, and the older you get, the MORE restrained does it become due to the running down of hormones! - the more you talk about other people and their thoughts (yes, Va., even if only in your head), and the less able you are - everybody is - to create original thought for yourself, daily, with purpose, with intention, with as much creativity as you are able every time.
"Who ME?! Surely you must be kidding! My thoughts are always original, enlightening, consciousness-expanding, mind-blowing. Lemme tell you about it!"