Speculation on the emigration theory is based on the idea that, by the 13th century, overpopulation of the area resulted in the oldest son owning all the land and power (majorat), leaving the rest as serfs. It has also been suggested that one reason the emigration of the children was never documented was that the children were sold to a recruiter from the Baltic region of Eastern Europe, a practice that was not uncommon at the time. In her essay "Pied Piper Revisited", Sheila Harty states that surnames from the region settled are similar to those from Hamelin and that selling off illegitimate children, orphans or other children the town could not support is the more likely explanation. She states further that this may account for the lack of records of the event in the town chronicles. In his book "The Pied Piper: A Handbook", Wolfgang Mieder states that historical documents exist showing that people from the area including Hamelin did help settle parts of Transylvania. Transylvania had suffered under lengthy Mongol invasions of Central Europe, led by two grandsons of Genghis Khan and which date from around the time of the earliest appearance of the legend of the piper, the early 13th century.