Suffering from long or repeated infectious illnesses, including those contracted in day care, can lead to children reaching adulthood with shorter-than-normal height and even passing this on to their own children, grandchildren and great-grandchildren. This was the conclusion of research on the mechanism causing abnormal heights in children by researchers at the Techion-Israel Institute of Technology and Rambam Medical Center in Haifa along with the University of Goeteberg in Sweden. The researchers identified a mechanism that explains half of all heretofore unexplained cases of abnormal shortness by using an "evolutionary theory of life history." Prof. Ze'ev Hochberg of the Technion's Rappaport Medical Faculty and colleagues found that future body size was mostly determined during the transition from infancy to childhood. This usually occurs between the ages of six and 12 months, and every month of delay causes the child's future height to fall by 0.9 centimeters. Thus, if the transition occurs at 15 months instead of an average of nine months, the adult will be 5.4 centimeters shorter than expected. In an article just published in Pediatric Research, the physicians and scientists note that the strategy of evolutionary adaptation and "plasticity" suits human size to the energy potential in an individual's surroundings. "People, like animals, developed the ability to survive energy crises by reducing the size of their bodies. This occurs in children suffering from malnutrition, but also in children who are sick for a long period or repeatedly due to frequent infection at the critical age. "Short-term evolutionary adaptation to energy crises leads to a reaction suited to the individual's energy stores. The result is shortness. This adaptation is even transferred to future generations, so an energy crisis in one of the parents (usually the father) or grandparents will carry on to their descendants and cause shortness up to the third or fourth generation," they wrote. "A large human body is a trade-off between evolutionary advantages and shortcomings," the researchers said. "We argue that a person's height will largely be determined during this transition period, and a delay affects lifelong height. It is responsible for 40 to 50 percent of cases of shortness among children and adults in developed countries and much more in developing nations."