21
Feb
10

Wrong again…

Remember Harlow’s monkey experiment I mentioned recently? Well, I’m convinced journalists ares actively trying to misrepresent research by tacking on a bit of nonsense that have already been tested. In monkeys, the development of a fear of snakes, particularly, has been demonstrated by Michael Cook and Susan Mineka back in the late 1980s. Crickets may respond differently, but let’s talk specifics. The research (which can be found here-side note to science journalists: see how difficult it is to include a hyperlink to the relevant research?) does show that the cricket offspring do respond to scent cues to the wolf spider without being exposed to a spider after birth; i.e. they don’t have to learn “hide from spider” if their mothers were exposed to a spider while gravid. Can parents of humans have an effect on their offspring before birth? Of course, but passing on phobias doesn’t seem to be one of them in primates. It does seem to be the case in these crickets, maybe.

I’m certainly not trying to take anything away from the research; it beautifully demonstrates how specific cues and responses may be passed on from mother to offspring in crickets, but it requires the mother to be exposed to the stressor while gravid. The research they point to as “evidence” is actually a fairly well written article on the ability to detect hidden snakes and spiders in 3-year-old children and adults. They don’t overreach the research implications at all (probably because it already relates to humans). Using this research as evidence that “humans instinctively fear snakes” raises the obvious question: explain all the humans that DON’T fear snakes (myself, for example). It is possible that “snake” and “spider” are areas of “prepared learning” which are easily recognized by the brain, but precisely how to respond to these is not determined. To quote Matt Ridley, for he is much more eloquent than I am,  describing Mineka’s monkey experiments:

[…] She hypothesized that monkeys must acquire a fear of snakes vicariously, by observing the reactions of other monkeys to snakes. Lab-reared monkeys, not getting this experience, do not acquire the fear. She first took six baby monkeys, born in captivity, to wild-born mothers and exposed them to snakes while they were alone. They were not especially afraid. When given the opportunity to reach over the snake to get some food, the hungry monkeys were quick to do so. Then she showed them snakes while their mother was present. The mother’s terrified reaction was immediately picked up by the offspring, which thereafter, was permanently frightened, even of a plastic model of a snake. Next, she showed that a monkey could acquire a fear of snakes from a monkey that had acquired its own fear in this way.

For her next trick, Mineka wanted to see if it was just as easy to get monkey to teach a naive monkey to fear something else, such as a flower. The problem was how to get the first monkey to react with fear to a flower. Mineka’s colleague, Chuch Snowden, suggested she use the newly invented technology of videotape.If monkeys could watch videotapes, and learn from them, then the videos could be doctored to make it appear that the teaching monkey was afraid of a flower, when it was, in fact, reacting to a snake. It worked! Monkeys had no difficulty watching videotapes of monkeys and reacting to them as they did to real monkeys. So, Mineka prepared tapes in which the bottom half of the screen was spliced in from another scene. This made it appear either that a monkey was calmly reaching over a model of a snake to get at some food or that a monkey was reacting with terror to a flower. Mineka showed the doctored tapes to naive, lab-reared monkeys. In response to the true tape, (fear to snake, nonchalance to flower) monkeys quickly and robustly drew the conclusion that snakes are frightening. In response to the false tapes, (fear to flower, nonchalance to snake) the monkeys merely drew the conclusion that some monkeys are crazy.

I am not suggesting that stimuli in utero have no effect on developing offspring. I am suggesting that reactions to specific external stimuli do not exist in primates the same way as in crickets. I would be curious to know if associatively learned fears to other scents can be passed on, since this could tease out a potential mechanism for this observation. I would be interested in finding out of a mechanism for this inherited learning is ever discovered. I don’t really know enough about insect olfaction to speculate further.

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