Now Joseph Courtney and Ad Bax, a pair of researchers at the National Institutes of Health in Bethesda, Maryland, think they may have worked out why.

目前，马里兰州贝塞斯达国家卫生研究院的两位研究员约瑟夫·考特尼和艾德·巴克斯认为他们可能已经找到了原因。