What would it feel like if all these tremendously powerful wild cats—lords of all they surveyed—were out there stalking us with their teeth and claws? How did our ancestors deal with so many predators casting around for their next meal? One of us (DH) experienced an hour or two that might have supplied the tiniest fraction of those ancient hominid feelings.
"What if they weren't satiated and sleeping?" popped into my mind as I was sitting under an acacia tree in Mikumi National Park, Tanzania, with two park rangers. The tree was decorated with a dozen sleepy lions draped over branches like huge tawny tinsel on a Christmas tree. It was a favorite after-feeding hangout of the lions (who don't ordinarily take to trees for siestas). My official government hosts had the requisite rifle— just in case—but no one felt anything like danger. This must be how prey animals feel when predators are obviously not on the hunt, I mused. I couldn't even conjure up the panic that 12 lions would have aroused if I hadn't been so assured by their full stomachs and heavy-lidded eyes. Later, after we began writing this book, I realized I had had an experience not unlike a far-distant hominid relative. Obviously, prey species cannot live in a state of terrified panic all the time—the stress would kill them before the predators did! There has to be a certain sense of safety between infrequent moments of all-out terror. Weren't my colleagues and I under the acacia tree experiencing the same placidity that impala exhibit when they calmly graze in the presence of resting lions? Yes, there was a weapon someone could grab; but to tell the truth, if a lion had jumped or fallen out of the tree, no human possesses the reaction time necessary to assess the situation, aim a gun, and pull the trigger before a lion leaped onto . . . me? (Well, in retrospect, maybe these little excursions aren't such a bright idea. Maybe I was falling into the "stupid Yellowstone tourist" trap . . . you know, the guy who places his little boy next to a bear so he can get a really cute picture of their vacation.)
Recalling and discussing this experience brought up some colossal questions:
1. What is the physiological basis for fear?
2. Why are people who do not experience the impact of predation still so afraid of predators?
3. How could early hominids (or any preyed-upon species for that matter) withstand the psychological pressure of predation?
Question number 1 is probably the most straightforward to answer.34 The anatomy of fear includes dilation of pupils (to increase visual cues to danger), dilation of bronchioles in the lungs (to increase oxygen uptake), a spike in blood pressure and heart rate (to provide the brain and muscles with more fuel), breakdown of glycogen in the liver (to provide instant energy), flooding of the bloodstream with adrenalin (to guarantee a strong defense), contraction of the spleen (to pump out white blood cells just in case they are needed), preparation to void the bladder and colon (in anticipation of violent action), constriction of capillaries in the stomach and gastrointestinal tract (to divert blood to the muscles), and piloerection of hair (the strange phenomenon of body hair "standing on end"—perhaps to enhance size). All of these are accomplished through the work of a primitive part of the brain called the amygdala. The amygdala sends an all-out systems alert to the central and autonomic nervous systems that gets these physiological responses up and running.
Question number 2 (why would humans retain such an undiluted fear of predators without personal experiences?) is also answerable, but only because of 25 years of research by Joseph LeDoux of New York University. The amygdala also stores memories of fear, danger, or threat. It can be a totally unconscious memory that is retained and kicks in only when sight, sound, or touch prompts it. "Conditioned fear" is the amygdala's specialty. This is what makes you freeze before you have time to process in your cerebral cortex whatever it was that scared you. The amygdala portion of the brain is found in the brains of many vertebrate species and functions in the same way—it's natural selection's best shot at giving organisms an edge in a dangerous environment. But "conditioned fear" doesn't mean that you have, for instance, survived a mauling by a wild lion so that the next time you see a lion all the fear responses kick in. It does mean that large, predatory animals that pop out of nowhere (and scary stories told or read about the same) have been parked in the amygdala and underlined as extremely important. One way to explain this adaptation is that
Our brains seem to have been designed to allow the fear system to take control in threatening situations and prevent our conscious awareness from reigning. This may have been an optimal design from predator-rich environments in which survival was a minute-by-minute question. . . . The fact that the amygdala's basic architecture reappears in so many species is testimony to its evolutionary importance: Natural selection doesn't tinker with components that have proved essential to basic survival. Of course, the persistence of the low road [the non-cortex reaction] in a world where predators are largely nonexistent may no longer be adaptive, but that's the trade-off of human culture.35
The answer to our final colossal question (how can the threat of impending predation be tolerated psychologically?) is speculative since scientists do not know all of the neural pathways that maintain mental equilibrium in the presence of extreme but intermittent stress. War zones provide some clues since posttraumatic stress disorders ("shell shock") are now accepted as a common aftermath of combat experiences even though the soldiers may seem to relax and behave normally for short periods between battles. We suggest that the only possible answer to this question lies with continued observation of prey species. We must refer to other species for information on how it is possible to graze happily (if you are an impala) while in the presence of lions. As primatologists we firmly believe—based on observation of wild primates—that prey go on with the minutiae of their lives between instances of predator activity. Under normal ecological conditions, the adrenaline rushes subside after the predator attacks, and hormones revert to neutral gear—except for the unlucky individual who became the predator's meal. Did our ancestors have respite from constant psychological terror produced by the presence of large cat predators? A resounding "yes." We primates are amazingly resilient. There is a threat of attack by a predator and all hell breaks loose. The predator leaves the area (with or without a meal) and the primates soon resume their lives of foraging and social interactions. Wild primate lives are not constant battles to stay alive, nor was there a continuous state of terror for Man the Hunted.
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