Anyone who is highly sensitive must often wonder: why am I the way I am? Is it nature, nurture, or both? Lately a number of scientific findings and popular theories indicate that, undeniably, the answer is both.

To begin with, a British study shows how an important genetic variant makes some people more sensitive to their emotional environment - and more susceptible to anxiety disorders - than other people. This research, from the University of Essex, focused on the serotonin transporter gene. Serotonin itself is a neurotransporter, a chemical released into the gap between nerve cells, and the serotonin transporter is a protein that plays an important part in that cross-nerve signaling. Once a signal has crossed from one nerve cell to another, the serotonin transporter removes serotonin from the gap and transports it back into the initial nerve cell, where it can be reused for the next signal.

Now, the gene that encodes the serotonin transporter varies across the human population. Some people carry a ‘short' version of the gene, which results in them having fewer copies of the serotonin transporter and, therefore, higher concentrations of serotonin in the gaps between neurons. Other people have a ‘long' version of the gene, leading to more copies of the serotonin transporter and lower levels of serotonin in the cross-neuron gaps.

Previous studies had found that people with a short version of the gene tend to pay more attention to negative or potentially threatening information. This negative bias is characteristic of many anxiety disorders, such as depression, post-traumatic stress disorder, and irritable bowel syndrome.

Remarkably, the University of Essex team found that people with the short version of the serotonin transporter gene were not only more sensitive to negative information when tested, but more sensitive to positive information! In the words of the lead researcher, Dr. Elaine Fox, such people "are likely to be far more reactive to both very negative situations, such as a car crash, and very positive ones, such as a very supportive relationship." The short version of the gene, she says, can be viewed as providing enhanced adaptability as well as greater vulnerability in the first place. In contrast, people with the long version of the gene are likely to be less influenced by negative stimuli but also less able to benefit from a highly positive emotional environment - since their reactivity in the different experimental conditions barely changed. (link:

Orchids and Dandelions

The serotonin transporter gene - and others like them - can be characterized as an "orchid" gene, after the flower whose blooms are spectacular but which also requires great care to cultivate. If the environment is supportive, a person with orchid genes will probably thrive - and possibly succeed in spectacular ways. But if neglected, or subjected to negative emotional input, such a person may develop any of the anxiety disorders and find her or himself wilting (to stay with the flower analogy). Other people, however, are more resistant to the vicissitudes of life and aren't quite so subject to the relative quality of their nurturance. They're more numerous and more hardy. They are the "dandelions."

The orchid-dandelion hypothesis has been expressed principally by University of Arizona developmental psychologist Bruce Ellis and University of British Columbia developmental pediatrician W. Thomas Boyce, and presented in a more popular vein by author David Dobbs. People who are orchids, they point out, have a heightened genetic sensitivity to all experience - but a person's environment plays an equally important role. They term it biological sensitivity to context. Orchids are more susceptible to stress and tumult but whether they go on to develop various health conditions ultimately depends upon their emotional environment.

Incidentally, humans aren't the only species with variations in reactivity among individuals. The same has been found in mice. The ones who seem most vulnerable to stress are also more likely to fall ill. (link: Such variability may eventually be disclosed as a feature of all mammals.

Just as the divide between mind and body is disappearing - thanks to all manner of discoveries in the field of psychoneuroimmunology (the discipline that studies connections between the nervous, immune, and endocrine systems) - so, too, clear and fast distinctions between nature and nurture are on the way out. The latest findings indicate that environmental stimuli can be as deterministic as genes were once believed to be, and the genome can be as malleable as only environments were believed to be. To discriminate between nature and nurture in this way seems as futile as asking which feature of a rectangle - length or width - makes the most important contribution to its area. (link:

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