The terms of Marriage (Part 2): Investment & Inheritance

I covered quite a bit in the first part of this blog: The terms of Marriage (Part 1): Marriage Systems. If you look at the date stamp of Part 1 (I recently edited as I wasn’t happy with a section), I wrote it almost two years ago to the day. It wasn’t supposed to be that long, and I have probably drafted Part 2 approximately three times, but every time I wasn’t happy with it or found something better to write about. However I find inheritance systems extremely interesting as they can be applied to real life examples. To prevent another binned draft, I am therefore going to ask questions, and then answer them, and hopefully you will find it equally fascinating (click on each question to go to it).


(1) What does the Indian caste system, gypsies and nunneries all have in common?

(2) What does age and status have to do with abortion?

(3) How did Napoleon Bonaparte accidentally cause the French to marry their cousins?

(4) Why do the rich breed less than the poor in Western society?


What does the Indian caste system, gypsies and nunneries all have in common?

A study by Dickemann in 1979 looked at female infanticide in the Indian caste system. The study found that this was extremely common in the highest castes of the Rajput tribes before the twentieth century. The rules of the system dictate that woman can marry from the same caste or higher, while men can marry from the same caste or lower. This caused a problem for females in the highest caste as they could only get mates from the same caste. To reduce this problem, females of the highest caste were killed (Barrett et al. 2002). In this system, it is likely that higher castes will invest more in sons, whereas lower castes will invest more in daughters.


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This is an example of the Trivers-Willard Effect whereby “…a parent will maximise its fitness by biasing investment towards the sex of offspring that provides the highest return (measured in terms of the offspring’s own reproductive success or fitness) on the level of investment that the parent is capable of providing” (Barrett et al. 2002, p.388).

This effect is also seen in Urban Hungarian Gypsies who were found to invest more in their daughters than sons, through suckling their first-born daughters for longer, more likely to abort a subsequent pregnancy after a daughter than after a son (which suggests that the mothers wanted to continue investment in the preferred sex), and allow their daughters to continue in secondary school which had to be paid for, for longer.
For the gypsies living in the city, it would pay to invest in daughters because compared to the Hungarians, the gypsies were seen as lower down in the social strata. Being of lower social status, male gypsies would be seen as unattractive husbands, and would therefore have lower reproductive success than gypsy females, who could marry Hungarian men.
In rural gypsy communities however, the marrying up of daughters is less likely to occur. The investment in daughters is therefore thought to occur because of the benefit the daughter has to childcare. A bit like the system in marmosets whereby older siblings look after their younger siblings, the gypsy daughters look after their younger siblings, allowing the mother to increase her own reproductive output. Indeed, women with first-born daughters were found to reproduce for significantly longer than those with first-born sons. However, this in turn had a negative relationship with the daughter’s own reproductive output, although this may not effect her inclusive fitness, as she is helping out her genetic siblings (Barrett et al. 2002). I do wonder though what the males position is in this society. For instance, if both first-born females and males were to help with childcare of their siblings, then there would be no need to invest in one sex over the other.

In fifteenth and sixteenth century Portugal, nobility families were arranged into higher and lower ranking lineages. High ranking men had higher reproductive success than lower ranking men as they had more resources (see Part 1 for explanation) and were more likely to marry and have more illegitimate children. In the lower ranking families, investment was towards daughters. Whereas female infanticide occurred in the Rajput tribes of the highest caste, the high ranking Portuguese families instead put their excess daughters (the ones who couldn’t find a husband) into nunneries. If a husband became available, the nun became marriageable again. For the excess sons, they were sent off to war. If the men didn’t die in battle, they could only hope to gain spoils of war and then become a more attractive partner.

During the early mediaeval period, the Portuguese allowed all sons to inherit the estate. However, once Portugal had been effective in expansion and conquest of the Arab-dominated southern parts of the Iberian Peninsula, expansion became harder to achieve. Inheritance in the thirteenth century therefore changed from all sons inheriting to only the eldest son inheriting the estate. Inheritance and expansion seem very much connected here with Boone (1988) arguing that “…the pressure created by a growing pool of disaffected landless younger sons [in Portugal] was directly responsible for the initiation of the Portuguese explorations and the resulting colonial episode – with the explicit encouragement of the monarchy who saw this as a useful way of diffusing a growing social problem” (Barrett et al. 2002, p.220). I wonder in part, if this was also what caused Viking exploration, and their need to label items as their property.

Porto, Portugal old town cityscape on the Douro River with traditional Rabelo boats.

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What does age and status have to do with abortion?

There may be many reasons for infanticide to occur, for instance; paternity certainty, offspring quality or maybe scarcity of resources. Abortion is also a form of infanticide, but an acceptable form, as the child is more a bunch of cells (like when you itch your arm and cells drop off) than a person. On a study performed on women in England & Wales, it was found that as age increased in single women, the less chance that the woman would opt for an abortion, whereas the reverse occurred in married women. This is likely because as a young single woman with a child you are more likely to hamper your prospects of marrying – marriage equals resources and the potential of increased reproductive success. As the single woman gets older however, the likelihood of marriage may decrease and the cut-off for childbearing grows closer. For married women it is the reverse however because older married women most likely want to limit family size and protect their existing parental investment (Dunbar et al. 2007).


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How did Napoleon Bonaparte accidentally cause the French to marry their cousins?

Napoleon didn’t want the French aristocracy to have too much political power. At the time, the French aristocracy practised primogeniture (inheritance by the eldest son), but Napoleon instead promoted the Code Civil. Meaning that land would now have to be divided equally amongst all children and hopefully reduce wealth in each successive generation. Instead of the Code Civil doing what Napoleon intended, power and inheritance did not get smaller. Within two generations, the French nobility had reduced their family size to two children and married cousins. The size of the land therefore was prevented from being chopped up (Barrett et al. 2002).


Click here for source

Why do the rich breed less than the poor in Western society?

One would think that more resources meant being able to breed more, but one thing you hear a lot, is how many children those on benefits have. Take this article by the Daily Mail for example. Surely, to maximise inclusive fitness, the rich should be breeding more.

An individual named Pérusse (1993) investigated this among French Canadians and found that high status males do appear to get more mating opportunities than lower status males, but contraception prevents their reproductive success. Not only this, but inheritance also comes into play. For reproductive success to continue, you want your children to have children, and children will become more successful with the more investment you can put into them, and the inheritance they will gain. The cost of investment and inheritance they gain is reduced with every child you add, so it is a better strategy to invest more in fewer children. On the other hand, if you are poor, you have little resources to add anything. It makes more sense to have more children so that they can either help raise siblings, or possibly to increase chances of reproductive success (Barrett et al. 2002).


As I wanted to have this blog post with many different questions, the information gained was taken from these two books which I highly recommend you read, if you are interested. I should have gone to the original sources outlined in the books, but as I said, I wanted a culmination of questions, rather than to look meticulously at each study, which I do in other posts. If you do want original sources, the books are your first port of call, but if you are having trouble getting hold of them, you can message me on this page.

Barrett, L., Dunbar, R. & Lycett, J. 2002. Human Evolutionary Psychology. New York: Palgrave Macmillan

Dunbar, R., Barrett, L. & Lycett, J. 2007. Evolutionary Psychology: A Beginner’s Guide. Oxford: Oneworld.

Featured Image: Due to the update WordPress has done, putting in links causes endless aggravation. Click here to be taken to the featured image instead.


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