You're wrong. And I think you know it, but if you disagree, then I invite you to prove your assertion.
I do know that there are folks in Russia right now calling for the legalization of polygyny in order to boost their sagging birth rates. Do they know something you don't?
Perhaps they're laboring under the same misconceptions that you are.
"Obviously?"
Are you serious?
How much "access" is required?
I guarantee you that a man with three wives would not find it difficult to impregnate all three of them in the course of any given year.
A motivated man could probably impregnate all three in the course of any given day.
The question isn’t whether or not the man could conceivably impregnate them all within the course of any given year. The question is whether or not the female is more likely to conceive with a man who is also partner to other women versus conceiving with a man who is partner to her alone. Are you seriously suggesting that the women who are sharing their husbands will have as much access to her mate as the monogamous woman? There are some people who are quite fertile and would have no problem conceiving in a situation wherein they are sharing their mate. However, there are other people for whom fertility isn’t so easy, and having constant sexual access to one’s partner will help determine the success of conception. In addition, the other factor to be considered is not only conception, but the survival rate of the subsequent offspring.
There are mixed reports regarding this issue, by the way, but it certainly isn’t clear-cut as you suggest. There is a lot of research out there to access. I know you dislike it when I actually quote sources that have studied the issue, but for the benefit of others, here are just a few:
Human Mating Systems: Polygyny (Robert Quinlan, ANTH 468, Washington State U.)
There was not a big difference in the fertility (number of births per woman) of polygynous versus monogamous Dogon women. Polygynous women tended to have more lives births than did monogamous women (figure 2). This finding might support the polygyny threshold model. Recall, however, that there are two determinants of fitness: survival and reproduction.
In contrast to fertility, there was a huge difference between polygynous and monogamous mothers in their child mortality rates (figure 3). Polygynous mothers could expect to lose about 1 in 3 of their children in the first five years after birth. Imagine that! If you had three children you would be almost certain to lose one of them. Monogamous mothers only lost about 9% of their offspring in the first five years. So, the fertility data support the polygyny threshold model, but the child mortality data support the male coercion model. From a quality of life standpoint monogamous women are better off – they have fewer pregnancies over their life (I hear that pregnancy is not that much fun) and they fewer of their children die. But what about fitness (genetic representation in future generations)? Reproductive success (number of surviving offspring) is one of the most common measures of fitness available. Number of surviving grand-children would be a better measure of fitness, but you can imagine how hard it would be study that among living women.
http://www.wsu.edu/~rquinlan/polygyny.htmTitle: Differentials of fertility between polygynous and monogamous marriages in rural Bangladesh.
This paper discusses polygynous marriages in rural Bangladesh, using marital status and birth registration data from the Demographic Surveillance System (DSS) of the International Center for Diarrheal Disease Research, for the period 1975-79. Of all the marriages recorded during this period about 5% were polygynous. To identify the women polygynously married, 1974 census data of the DSS area were used. The difference in age at marriage between the polygynous groom and his subsequent wife was 15 years on average. The socioeconomic indicators studied were education, occupation and area of dwelling space. In general, these indicators between women in monogamous marriages were significantly higher than between the women in polygynous unions. During the period 1976-79, 863 polygynous marriages were recorded (4.9% of all marriages in the study area). Polygynous marriages were found to be less frequent among men with 2ndary and higher levels of education. The highest proportion of polygynous marriages occurred among husbands with no schooling or Koranic education. The general fertility rate of women in monogamous marriages was significantly higher than for women in polygynous marriages, overall and in all age groups except 20-24. During the period 1975-79, the mean number of liveborn children for monogamous women was higher than that of polygynous women.
http://www.popline.org/docs/0026/041950.htmlTitle: Fertility of women in polygynous unions in rural eastern Nigeria.
Findings, based on a retrospective fertility survey of 531 women in polygynous marriages and 1141 women in monogamous unions conducted in 16 traditional Ngwa Ibo villages in eastern Nigeria, supported the contention that polygyny reduces fertility; for polygynous wives, both the age specific fertility rates and the mean parity for all age categories was lower than for monogamous wives. Since the mean parity for women, aged 45-49, was 6 for polygynous women and 8 for monogamous women, it is apparent that the two groups differed widely in completed family size. When the mean parity of all wives was compared to the mean parity for successive polygynous wives, there was a 15% reduction in fertility for 1st wives, a 37% reduction for 2nd wives, and a 46% reduction for all succeeding wives. The association between reduced fertility and polygyny was attributed to the wide age differential between polygynists and their wives; for all types of marriages, husbands were on the average 11 years older than their wives, but for polygynous men the age differential ranged form 13 to 18 years, and 78% of the polygynous men were over 50 years of age. In comparison to other African regions the incidence of polygyny for the Ngwa Ibo was low, but the intensity was high; only 16% of all married men were polygynists, but each polygynist had an average of 2.8 wives. The low incidence of polygyny in this population may indicate that the practice of polygyny is dying out; therefore, increased birth control efforts may be needed to offset the loss of polygyny as a fertility depressant. Tables included 1) age specific fertility rates and mean parity by marriage type and by age; 2) mean parity by marriage pattern, marriage duration, age, and by wife order; 3) ideal number of children by wife order; 4) % distribution of spouses by marriage pattern and age; 5) % distribution of polygynous wives, aged 15-44, by husband's age; and 6) incidence, intensity, and ratio of married women/100 married men for Ngwaland and several African regions.
Now if a society was suffering a serious shortage of males, then polygyny would increase the birth rate in general. But as long as the society was not suffering from a server male shortage, and females who were interested in marrying could generally do so, then polygyny would not increase the over-all birth rate. And if it did increase the overall birth rate, the higher mortality rate in those offspring negate the effect.
Think about it, Will. This is common sense as well as research. Women are more likely to conceive if they have frequent sex with their partner. Women who are sharing their partner will have less frequent sex than they would in a monogamous setting. In addition, there will be less material/physical/emotional support of the subsequent offspring when the male is dividing his means between more than one household. Less material/physical/emotional support results in a higher mortality rate.
So are you just going to ignore the real cost of polygyny, which is the disaffected underclass of males with no hope of mating?