Kościński K, Kozłowska-Rajewicz A, Górecki M T, Kamyczek M, Rózycki M
Department of Human Population Ecology, Institute of Anthropology, Adam Mickiewicz University, 61-701 Poznań, Poland.
Homo. 2009;60(2):159-83. doi: 10.1016/j.jchb.2008.02.003. Epub 2009 Jan 21.
Previous studies unanimously confirmed the existence of a dependence of human body size on the month of birth. The cause of the phenomenon has not been identified yet, although some possible causes were proposed e.g. seasonal changes of climatic and nutritional conditions. This study explored the issue in an animal model of 20,513 pigs. We found that body weights of 6-month-old pigs were the highest for subjects born in February, but for 2-month-old pigs the peak fell in May. Any statistical correlation between the month of birth and later body weight may be induced by (1) a long-term effect of the month of birth on further growth potential (LTE), or by (2) a short-term effect of seasonal factors differentiating the growth rate (STE), so we developed a mathematical method to separate the effects. The analysis proved that (1) the observed correlations resulted only from the STE, with May-June being the months of the highest growth tempo, and that (2) there was no significant LTE. The short-term effect was responsible for differences between patterns of weight for 2- and 6-month-old animals by the month of birth: since a pig monthly gain of weight increases with age, it is favorable for it to be born in February to attain the greatest weight at the age of 6 months, whereas 2-month-old piglets are heaviest when born a month or two before the May/June optimum for growth. The lack of a long-term effect of the month of birth on pigs' weight supports the hypothesis of the cultural character of factor(s) responsible for the relationship between the month of birth and later body size in humans.
以往的研究一致证实，人体大小与出生月份之间存在相关性。尽管有人提出了一些可能的原因，如气候和营养条件的季节性变化，但该现象的成因尚未确定。本研究在20513头猪的动物模型中探讨了这一问题。我们发现，2月份出生的6月龄猪体重最高，但2月龄猪体重峰值出现在5月份。出生月份与后期体重之间的任何统计相关性可能是由以下两种情况导致的：（1）出生月份对后续生长潜力的长期影响（LTE），或（2）区分生长速率的季节性因素的短期影响（STE），因此我们开发了一种数学方法来区分这两种影响。分析证明：（1）观察到的相关性仅源于STE，5月至6月是生长速度最快的月份；（2）不存在显著的LTE。短期影响导致了2月龄和6月龄动物出生月份体重模式的差异：由于猪的月增重随年龄增长，因此2月份出生有利于其在6月龄时达到最大体重，而2月龄仔猪在5月/6月生长最佳期前一两个月出生时体重最重。出生月份对猪体重缺乏长期影响，这支持了关于人类出生月份与后期身体大小之间关系的影响因素具有文化特性的假设。
