Prefatory reading: http://en.wikipedia.org/wiki/Demographic-economic_paradox
Prosperous people generally have less babies than poorer people. This seems contrary to what I would expect, from an evolutionary perspective.
Western places have great prosperity and thus great caloric abundance. Typically, when animals experience caloric abundance, they increase their population size.. historically humans seem to have fit this pattern just fine even with the advent of agriculture (i.e. the human population size exploded into the billions after agriculture). Now however, after grasping the extent of influence diet can hold over general health and behavior, it seems like a decline in dietary quality might be a good explanation for the decreased fecundity seen in prosperous peoples.
the general idea being:
1) Increases in wealth seem also to bring increases in the westernization of a group's diet. i.e., Chinese start becoming more wealthy, and suddenly you see more Coke and McDonals popping up around China. If a we believe this to be true, and if we believe a Western diet is poor in quality, then we can say generally wealth brings a decline in dietary quality.
2) A western diet, despite caloric abundance, could reduce fertility, directly via infertility and indirectly via something like a general drop in libido or desire to reproduce and such? i'm talking something like this http://en.wikipedia.org/wiki/Francis_M._Pottenger,_Jr.#Meat_study , with the cats receiving adequate calories and continuing to reproduce, but having fertility progressively decline and disease progressively increase over the generations due presumably to the cats being metabolically messed up from inadequate diet.
Basically the question is, to what extent, if any, can dietary factors explain the inverse relationship between wealth and fertility currently observed across the world?
Some sub-questions include:
-are Western diet eaters currently in the middle of walking down a path like Pottenger's cats (see above), with evidence for this being how kids today are expressing diseases that were once thought specific to adults?
-if animals are in an abundant calorie environment, but are metabolically messed up somehow either from dietary deficiencies or damage, do they have less babies? If so, is this because of increasing infertility, or are the animals fertile but unwilling to pursue mating rituals/sex as often?
-If western nutrition were 'fixed' (made more in line with that which yields health), would fertility rates in the west then rise to rates similar to those currently seen in more undeveloped nations/places? Or is (western) culture responsible for the decline in fertility, and thus improvements in everyone's health would not yield increases in fertility/birth rates.
any relevant evidence or reasoning for or against any of the above ideas would be awesome.
Correlation does not equal causation. There are plenty of variables other than diet that can more easily explain both an increase in prosperity and a decrease in childbearing. Examples: high paying jobs increase wealth but decrease the time/energy available to raise a child. Or the less children one has the more money you can save. I think diet plays a negligible role in the relationship stated in the question.
There are probably dozens of reasons including diet. I have noticed that some of the doctors first to jump on the paleo bandwagon have been fertility doctors. Diet makes a difference in fertility. HOwever, I think the main reason for decline in birth is the increase in specialization and city life. In an agrarian society, the kids pitch in starting at around 5 years old, feeding the chickens, watching the herds, helping with weeds, harvesting, etc. Kids are basically turned quickly into labor. Over the course of their childhoods, they pay their way and then some.
Whereas in industrialized society, they are expensive and most of them are too busy going to school, etc to give tons back to the household. THus the kids become an expense and having hoards of children is a drain on the household income. Families are more likely to have only a few children. And with current methods of birth control, we have that choice. I think that is the main reason birth has declined. Economics. -Eva
Some reasoning, if not outright answers:
First of all, there's no question that a calorie-rich but nutrient-poor diet will slow population growth in any organism; this is why brewers use yeast nutrient.
Second, women with more education tend to have less sex and/or more birth control. Those who are kept unschooled are typically socialized to believe that their social role is the production of heirs, farmhands, and the like. The more educated believe that a few well-educated offspring will be enough to cover their needs in old age, and often delay reproduction attempts until it's plumb too late.
Third, there are environmental problems beyond mere diet that can impact fertility. Certainly a dietary fix would help, but the ideal scenario would be to filter the heavy metals and toxic organic chemicals out of the oceans, land, and air. This is why some people's back-yard vegetables are less healthy than the ones grown on a proper organic farm.
Last, you can look at the whole problem as a system of multiple nonlinear constraints. Population will expand to the carrying capacity of the land. If all of Pottenger's cats die, then the local alley cats will keep on yodeling in the night eating their diet of rodents, large insects, and junk. Diet is but one constraint. At some points in the parameter space, diet will be the limiting constraint. At other points, it will be insignificant or meaningless.
Here in my corner of the west, I suspect that our food supply is not as nutritious as it should be. But at the same time, I expect that the very largest problem is that our misguided education system scares girls away from having children until they are simply too old. People have grown dependent on the schools for their socialization, and the schools teach birth control, but they fail to mention the significant drop in biological fertility around the age of 30.
Women today also have the right to work. That is as much curse as blessing. It doubles the size of the labor pool without doubling the demand for labor. This pushes the natural price of labor so low that most families require two incomes. The consequence is that women do not reproduce, lacking the energy and time. If we mean to promote fertility among the wealthy west, we need an FMLA that lasts four years for pregnant women, or else a return to the notion that women of childbearing age should not work unless forced by unfortunate circumstances.
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