Having a smaller family is a springboard for giving future generations the chance of greater prosperity, according to a Swedish study published on Wednesday.
Providing scientific support to what is anecdotal evidence, it says that in an advanced industrialised society, having fewer offspring means children benefit from greater parental investment and from inherited capital.
This translates into socio-economic success, which is transmitted over generations, the paper says.
Scientists from London and Stockholm pored over a remarkable database which assessed 14,000 people born in Sweden between 1915 and 1929 and all their descendants up to 2009.
Families that were smaller and from more prosperous backgrounds were linked to better grades at school, a university education and a higher income and social status, they found.
The benefits were greatest when the parents were also in a high socio-economic category. The advantages were enduring, because they carried over the four generations which were studied.
In the modern world, fertility rates -- the number of offspring per woman -- decline as a country becomes more prosperous, a phenomenon called the demographic transition.
The trend occurs first and most substantially among wealthier sections of society.
"One of our most interesting findings is that being from an initially wealthy household makes the benefits of small family size even bigger," said David Lawson, an anthropologist at University College London.
"Poorer households in contrast have relatively little to gain by limiting fertility, perhaps because the success of their children is more determined by broader societal factors, rather than investment and inheritance from parents, which is in short supply."
The research, published in the British journal Proceedings of the Royal Society B, touches on a keenly-debated aspect of Darwinian theory, said lead author Anna Goodman of the London School of Hygiene and Tropical Medicine.
"It's been a puzzle for evolutionary biologists," Goodman said. "It's not what you would expect, because as a species gets more resources, it has more offspring."
In this case, lower fertility was a success -- but in socio-economic terms, not in reproductive terms.
In the study, the first generation had an average of 3.2 children; their children had 1.7 offspring; the grandchildren had 1.8 children; and the great-grandchildren, as of 2009, had an average of 0.7 offspring.
