The test scores then sat in the vault for the next two decades, while the children from the study went their separate ways in life. They grew up, completed their educations, and turned into young adults. After 20 years had passed, the Blocks succeeded in tracking down 95 of their original 128 subjects, in the hope of measuring how liberal or conservative each of them had become. This time they asked the young adults, now age 24, to situate themselves on a five-point political spectrum. They also asked them to express their opinions on a number of highly partisan, hot-button issues. In particular, several of these questions measured their tolerance of inequality between the genders and between different racial groups. In addition, they were asked to describe any political activism they might have participated in during the intervening years.

The results, published in 2006 by the Journal of Research in Personality, were astonishing. In analyzing their data, the Blocks found a clear set of childhood personality traits that accurately predicted conservatism in adulthood. For instance, at the ages of three and four, the “conservative” preschoolers had been described as “uncomfortable with uncertainty,” as “rigidifying when experiencing duress,” and as “relatively over-controlled.” The girls were “quiet, neat, compliant, fearful and tearful, [and hoped] for help from the adults around.”

Likewise, the Blocks pinpointed another set of childhood traits that were associated with people who became liberals in their mid-twenties. The “liberal” children were more “autonomous, expressive, energetic, and relatively under-controlled.” Liberal girls had higher levels of “self-assertiveness, talkativeness, curiosity, [and] openness in expressing negative feelings.”

The Blocks’ experiment suggested that the roots of our political orientations emerge as early as the fourth year of life. But it raised further, essential questions: Would children from different regions or socioeconomic backgrounds diverge into similar personality groups? And how much deeper are the origins of these crucial personality traits?

When the Blocks’ findings are connected with other relevant studies in genetics, neuroscience, and anthropology, a composite image of our political nature begins to emerge. As this portrait of ourselves comes into focus, it shows what made some of those nursery-school children grow up to become liberals and some of them conservatives. It shows how deep the roots of our political proclivities extend, and why they have a similar influence on children in America, the Middle East, and most everywhere else.

The reason for these crosscutting commonalities is that political orientations are natural dispositions that have been molded by evolutionary forces. Taken together, those deeply ingrained political orientations form what could be called “The Universal Political Animal.”