Small Family Size Increases Wealth of Descendants but Reduces Evolutionary Success

[xchrom]

http://www.sciencedaily.com/releases/2012/08/120828190921.htm

ScienceDaily (Aug. 28, 2012) — Scientists have taken a step closer to solving one of life's mysteries -- why family size generally falls as societies become richer.

Evolutionary biologists have long puzzled over this because natural selection is expected to have selected for organisms that try to maximise their reproduction. But in industrialised societies around the world, increasing wealth coincides with people deliberately limiting their family size -- the so-called 'demographic transition'.

In a study published in Proceedings of the Royal Society B: Biological Sciences, researchers from the London School of Hygiene & Tropical Medicine, the Centre for Health Equity Studies (Stockholm University/Karolinska Institutet) and UCL (University College London) reject a popular theory put forward to explain the phenomenon. This 'adaptive' hypothesis proposes that low fertility may boost evolutionary success in the long term by increasing offspring wealth, which in turn eventually increases the number of long-term descendants because richer offspring end up having more children.

The researchers found that having a small number of children increased the economic success and social position of descendants across up to four generations, but reduced the total number of long-term descendants. They conclude that the decision to limit family size can be understood as a strategic choice to improve the socioeconomic success of children and grandchildren in modern societies, but this socioeconomic benefit does not necessarily translate into an evolutionary benefit.

The study indicates a conflict in modern societies between behaviours promoting social and economic benefits versus biological success. This contrasts with traditional populations in the developing world, where behaviours that promote wealth and social status usually lead individuals to leave behind more genetic descendants.

[Jim__]

1. They define "evolutionary benefit" as leaving behind more genetic descendants.

The study seems to be somewhat short-term to make that determination. Over 100 years we are looking at some 5 or 6 human generations. I wonder if large, poor families are more likely to survive into, say, the 25th generation than small, wealthy families.

I also wonder about the strain put on requisite resources by large families. It would seem that a region with a preponderance of large families is more likely to run out of resources than a region populated with relatively small families. Could a cultural preference for no-growth population be a long term evolutionary benefit for the dominant species on the planet? Is there an evolutionary benefit in an "intelligent" species to considering the long-term effects of large families?

Large numbers of descendants seem to endanger the long-term survival of humanity. I'm not sure how you can factor that into reproductive strategies for individuals.

[JackRiddler]

4. It's time to retire this as a concept of "success."

Selfish gene theory.

I mean, who cares? Someone like Genghis Khan is the most "successful" known human. Hooray!

[Fumesucker]

2. I have a more simple explanation I think..

In primitive societies children are labor that can be put to work quite young, they provide an economic benefit to the parents fairly quickly.

On the other hand in more wealthy and advanced societies children are or at least can be a large economic drain on parental resources that quite possibly will never pay off economically.

Having a child these days is an expensive proposition that puts the parent in the position of having a drain on their resources for at least eighteen years and quite possibly considerably longer than that.

People are making a rational decision to limit family size because a great many parents simply can't afford multiple children.

[eridani]

3. Lots of "evolutionary success" in Rwanda

Did they mention what happens to a population where women have 8 or so kids apiece for 30 years in a dry country gettting drier, and their descendents start slaughtering each other over land? OK, if they had big imperial armies they could overrun their neighbors and take what they need like advanced societies, but still.....