I have been blocked from commenting on Carl Zimmer’s nonsensical misrepresentations of cause and effect elsewhere, but I don’t want anyone to miss his latest misrepresentation of adaptive evolution and my comment on snake centric theory, so here it is.
Excerpt: “The fact that we share this bias toward snakes with monkeys suggests that it evolved in our common ancestors. When primates evolved some 60 million years ago, they adapted to living in trees, searching for food at night and sleeping in the canopy during the day. Snakes creeping through those trees were among their deadliest enemies.”
My comment: No evidence of biologically-based cause and effect supports that ridiculous misrepresentation of snake-centric evolution. All experimental evidence that details the connection from olfactory/pheromonal input to conditioning of epigenetically-effected changes in hormones, which affect behavior, supports the following representation of cause and effect in all mammals.
Excerpt 1 from Kohl (2013) “The epigenetic effects of nutrients on evolved differences in the diet and starch digestion of dogs and wolves (Axelsson et al., 2013) were detailed at the same time differences in the socialization of these subspecies were attributed to explorations involving only chemosensory input in 3 to 4-week-old wolf pups. For comparison, differences in starch digestion and exploration involving multisensory input in dogs begin a mere 2 weeks later (Lord, 2013). The differences in nutrient-dependent pheromone-controlled socialization, however, extend across a life-time of more aggressive behavior in wolves that have not been domesticated because less digested starch from their diet genetically predisposes infants to first respond to olfactory/pheromonal cues as they initially explore their postnatal environment.”
Excerpt 2 from Kohl (2013) “In the mouse model, the diet of the mice determines their nutrient-dependent pheromone production and social interactions with other mice.”
In all mammals the link from nutrient-dependent pheromone production to social interactions incorporates the startle response that can be compared in dogs and wolves. Imprinting on visual imagery associated with other members of the same species or subspecies occurs during the nutrient-dependent pheromone-controlled development of the brain and behavior. This imprinting clearly occurs via the involvement of the amygdala, which is an olfactory processing center of the mammalian brain. All evidence of biologically-based cause and effect links the epigenetic “landscape” to the physical landscape of DNA in the organized genomes of all mammals via effects on brain structures like the amygdala and associated emotions. Indeed, recent evidence clearly shows that the salience of visual input is associated with odors in humans. See: Olfaction spontaneously highlights visual saliency map.
From what is already known about the ability of mammals to recognize odor cues associated with food and with other members of their species or subspecies, it is easy to determine why humans, like other primates, would be startled by the movement of snakes or movements of other creatures larger or smaller than a human infant when they enter our peripheral vision. Like wolf pups, primates are startled by the movements associated with any other species. This is especially true given the extremely unusual movements of snakes, which are unparalleled by the movements of mammals.
Thus, the movements of snakes are immediately perceived, perhaps even unconsciously, as threats to primates. But the threat is not due to associated visual input. The threat is dependent on a lack of association with the movement of creatures that slither, creep, or crawl. Place the movements of such creatures and/or any other larger creatures in the context of a environmental surprise, or even in the context of the appearance of an angry face, and you will get a similar startle response or other aversive response. The responses are not due to visual input; they are due to associations made or not made in the context of olfactory/pheromonal input in wolf pups that ensure they will be averse to encounters with humans because a novel potential food source for them must be approached with caution, if it is approached at all.
To an undomesticated adult deer, the movements of a human adult are typically a threat associated with human odor. However, I have played with young deer merely by mimicking their movements (for example, lunging forward but quickly stepping back). Horses will respond to a rattlesnake without thought for past experience or anything they know about pit vipers. What makes anyone well-versed in neurobiology or evolutionary theory think that the human response to the visual imagery of a snake has anything at all to do with perception of threats from their evolutionary past? Science journalists owe it to their audience to inform themselves about scientific progress so that they do not continue to misinform their audience about cause and effect.