If you have a friend who never buys a round or who rarely pays their fair share, try not to get too angry.

Because being mean could be in their genes. Scientists have pinpointed a stretch of DNA that makes people stingy with their cash.

Around one in four of us carries the 'mean gene', which we have inherited from our parents.

In the study, those with the gene gave less money to charity than others.

Such thrifty sorts may also constantly cadge cigarettes, rather than buying their own, or regularly borrow cash for bus fares, but rarely pay it back.

Keen to look out for themselves - and their cash - they may also insist on totting up every item of food they have eaten in a restaurant, rather than simply splitting the bill equally.

The German researchers took samples of cells from inside the mouths of 101 young men and women and tested them for a gene called COMT.

The gene, which comes in 'G' and 'A' versions, is known to influence brain chemistry and the researchers believed it may do so in a way that affects how generous - or not - we are towards others.

The volunteers were given a gambling computer game to play and then told they could donate some or all of their winnings to a poor child in Peru.

To tug the heart strings, they were shown a picture of a girl called Lina and a bracelet that she had knitted.

The type of COMT gene did not affect how much the men and women won on the gambling game - but it did affect how much they gave to charity.

More than 20 per cent of those with the 'G' version gave all the cash they had won to Lina, but fewer than 2 per cent with the 'A' version were as generous.

On average, those with the 'A' version, or the 'mean gene' gave less than half as much to charity, the University of Bonn study found. But tight wads can't entirely blame their DNA.

Previous research has shown that our propensity towards generosity is only partly explained by our genes.

This means that other factors, such as upbringing, education and religion also play a role.

Spendthrifts, however, don't necessarily have the moral high ground. It is thought that one of the reasons we splash our cash or help others is simply because it makes us feel good.

Writing in the journal Social Cognitive and Affective Neuroscience, the researcher said: 'Altruism is defined as a selfless concern for the welfare of others.

'However, there is a great debate in the literature if true altruism really exists.

'People who doubt the existence of pure altruism argue that helping others is intrinsically rewarding and therefore they are exercising their personal interest to benefit their own selves rather than others.'

相關(guān)中文：

如果你有一位朋友從來(lái)都不請(qǐng)客，甚至都很少愿意AA制，那么你也不必太生氣，因?yàn)檫@很可能與他的基因有關(guān)系。據(jù)英國(guó)《每日郵報(bào)》11月4日?qǐng)?bào)道，科學(xué)家終于找到了“吝嗇基因”，這或許可以從遺傳學(xué)角度解釋小氣鬼們?yōu)槭裁窗彦X包捂得這么嚴(yán)實(shí)。

德國(guó)波恩大學(xué)研究人員提取了101位年輕男性和女性嘴里的細(xì)胞樣本，并在樣本中檢測(cè)一段名為COMT的基因。該基因分成G堿基和A堿基兩種類型，其能夠影響腦化學(xué)，進(jìn)而有可能左右人們慷慨與否。

在實(shí)驗(yàn)中，志愿者被要求去玩一個(gè)賭博電腦游戲，然后告訴實(shí)驗(yàn)人員他們?cè)敢鈱②A取的一部分還是全部獎(jiǎng)金捐贈(zèng)給秘魯?shù)呢毨和?。為了使?shí)驗(yàn)任務(wù)更加真實(shí)，實(shí)驗(yàn)人員還給志愿者呈現(xiàn)了一個(gè)名叫莉娜的秘魯貧困女孩的照片，以及一只由她編織的手鐲。

實(shí)驗(yàn)結(jié)果表明，擁有G堿基的志愿者有超過(guò)20%的人將他們贏的所有錢都捐給了莉娜，但是擁有A堿基（即“吝嗇基因”）的志愿者僅有不到2%的人能夠像G型人這樣慷慨。

通常，人類每4人中間大約就有1人攜帶有“吝嗇基因”，他們表現(xiàn)得特別注重自己的錢財(cái)，比如時(shí)常討要香煙而不是自己去買，或者定期借錢付公交車車票，但不怎么還錢。而且，那些攜帶“吝嗇基因”的人比其他人捐贈(zèng)給慈善機(jī)構(gòu)的錢更少。

不過(guò)，吝嗇的形成也不能完全歸咎于基因。之前的研究已經(jīng)表明，一個(gè)人慷慨與否只能部分地用基因來(lái)解釋，諸如撫養(yǎng)、教育和宗教等其他因素也有不同程度的影響。

（來(lái)源中國(guó)日?qǐng)?bào)網(wǎng)）