In this context he remarks that in The Geography of Hunger, the author Josue d Castro states that he thinks that "hunger, particularly protein deficiency, is an important factor in creating the problem of overpopulation." To support his hypothesis, de Castro cites several observations that support, such as the fact that cattle become sterile if overfattened. de Castro also produced the following table indicating that human populations display an inverse relationship between birth rates and amount of dietary animal protein.
Williams comments on this data (collected before the introduction of hormonal contraception):
"There seems, however, to be an interesting principle involve which should be further explored. Nature does take measures to prevent the extinction of a species, and when extinction is threatened––by starvation for example––it may be that an exaggerated sex urge is one of he devices used to perpetuate the race. It may be that this contributes to the high birth rate among people who are ill fed. A parallel is found in the area of plant physiology where t has been observed that plants often grow vegetatively as long as well fertilized, and tend to go to seed (reproduce) only when conditions become adverse.
The contrary possibility that a decrease in human birth rates could automatically be brought about by the provision of certain nutritional factors is at least worthy of study.”
Of interest, international data from 2004 also indicate that healthy life expectancy may also correlate inversely with animal protein intake. The following table based on WHO data shows that nations with lower animal protein intake and higher birth rates (e.g. Mexico, China, Thailand, India) generally have lower life expectancy than nations with higher animal protein intake and lower birth rates (e.g. Japan, Sweden, Switzerland, Italy).
These data suggest that vegetarian diets both increase population growth and decrease life expectancy. It does look like these two phenomena (increased birth rate and decreased life expectancy) arise from a common biological condition, and quite possibly de Castro and Williams have named it: animal protein (and perforce, methionine) deficiency.
I made a couple of important errors in my reasoning in this post:
1. The reduced fertility found in modern nations with higher protein intake could equally be interpreted as an indication that high intake of animal protein might increase the prevalence of infertility in humans. Thus, the data may indicate that low animal protein intake improves fertility.
In fact, we have data indicating that high animal protein intake poisons the uterus with ammonia, reducing the viability of embryos.
2. At the time the data was collected, the populations with low animal protein intake, high fertility, and low life expectancy also had relatively high infant mortality rates, which drives down the average the life expectancy. Thus, this data does NOT show that high animal protein intake increases longevity. Further, although most consider high infant mortality a terrible thing, in fact it is a pretty normal biological phenomenon; most organisms produce far more fertile seeds than surviving offspring. Modern medical care reduces infant mortality, possibly by preserving lives of weaker, more disease-prone individuals.
3. The most long-lived nation on the second table is Japan, but Japanese do not have a 'liberal' animal food intake by U.S. standards, although it is higher than in Mexico, China, Thailand, etc.. However, here again Japan has a low infant mortality rate compared to developing nations, making it look as though adults live longer in Japan than in those developing nations, when in reality the main difference is fewer deaths in infants in Japan versus developing nations.