Women on low-calorie diets or who skip breakfast at the time of conception are more likely to give birth to girls than boys, British scientists said on Wednesday.
New research by the universities of Exeter and Oxford provides the first evidence that a child's sex is associated with the mother's diet, and higher energy intake is linked to males.
"This research may help to explain why in developed countries, where many young women choose to have low-calorie diets, the proportion of boys born is falling," said Fiona Mathews of the University of Exeter.
There has been a small but consistent decline, of about one per 1,000 births annually, in the proportion of boys being born in industrialized countries over the past 40 years.
In humans, going without breakfast may be interpreted by the body as signaling low food availability, since it depresses levels of blood sugar.
Although sex is genetically determined by fathers, it is known that high levels of glucose encourage the growth and development of male embryos while inhibiting female ones, although the exact mechanism is unclear.
Mathews and colleagues studied 740 first-time pregnant mothers in Britain and found 56 percent of those in the group with the highest energy intake at conception had sons, compared with 45 percent in the lowest group.
In evolutionary terms, this correlation may make sense.
Males' breeding potential is strongly influenced by fitness, while females breed more consistently.
"If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times having a daughter is a safer bet," Mathews said.
Some researchers have been sounding alarms for years over the change in sex ratios in developed countries and have in the past blamed pollutants and synthetic chemicals such as those found in some pesticides which disrupt human hormones.
The latest findings were published in the journal Proceedings of the Royal Society B: Biological Sciences.
英國(guó)科學(xué)家于上周三稱，在受孕期間飲食攝入熱量較低或不吃早餐的女性生女孩的可能性更大。
英國(guó)埃克塞特大學(xué)和牛津大學(xué)聯(lián)合開(kāi)展的一項(xiàng)最新研究首次證明，孩子的性別與母親的飲食有關(guān)，在受孕期間攝入高能量食物的女性生男孩的可能性更大。
埃克塞特大學(xué)的菲昂納?馬修說(shuō)：“這一研究也許可以解釋為什么發(fā)達(dá)國(guó)家的男孩出生率持續(xù)下降，這可能與很多年輕女性選擇低熱量飲食有關(guān)。”
在過(guò)去40年中，發(fā)達(dá)國(guó)家的男孩出生率一直以每年約千分之一的比率小幅下降。
人在不吃早餐的情況下，血糖會(huì)降低，身體則會(huì)發(fā)出食物量不足的信號(hào)。
雖然從基因上來(lái)說(shuō)，孩子的性別是由父親決定的，但大家知道，人體內(nèi)葡萄糖含量較高能夠促進(jìn)男性胚胎的生長(zhǎng)發(fā)育、同時(shí)會(huì)抑制女性胚胎的生長(zhǎng)發(fā)育，但其中的具體原理目前還不清楚。
馬修及其同事共對(duì)英國(guó)740名生了第一胎的媽媽進(jìn)行研究。研究結(jié)果顯示，在受孕期間飲食攝入熱量最高的那組媽媽中，有56%的人生了男孩；而攝入熱量最少的那組只有45%的人生了男孩。
從進(jìn)化論角度看，這種說(shuō)法也是有道理的。
男性的生育能力受健康狀況的影響較大，而女性的生育能力則更為穩(wěn)定。
馬修說(shuō)：“由于男孩能夠‘傳宗接代’，所以在生活富足的情況下，女性為了生男孩而不惜大量投入確實(shí)可行，但在物質(zhì)匱乏時(shí)期，還是生女兒更保險(xiǎn)。”
近年來(lái)，一些研究人員一直在就發(fā)達(dá)國(guó)家的性別比率問(wèn)題發(fā)出警告，并將這一問(wèn)題歸咎于各種污染物以及一些殺蟲(chóng)劑中所含的化學(xué)合成物，這些物質(zhì)會(huì)損害人類的荷爾蒙。
這項(xiàng)最新研究結(jié)果在《英國(guó)皇家學(xué)會(huì)會(huì)報(bào)B：生物科學(xué)》上發(fā)表。
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