In Tiwi society, all the young men are married to older widows.  [I discussed the details in an earlier posting (Mind as a Coloring Book)]  Because all human females have a sharp decline in fertility beginning in their 30s, and ending with menopause, the Tiwi arrangement poses an interesting puzzle: How do the Tiwi reproduce themselves? Several features of Tiwi society help us resolve the puzzle. And when we put the pieces together, it helps us see why cultural diversity does not equal support for the Blank Slate viewpoint (or any of its modern disguises).

Powerful elder Tiwi males monopolize all the younger females, by marrying them at birth.

---------------------------------------------------------------------------------------------Although young Tiwi men are married to elderly women, a closer examination reveals that it's not because of a strong sexual attraction between the two age groups. Tiwi men are, like men in other societies, strongly attracted to young women. Unfortunately for the young guys, the powerful elder Tiwi men monopolize them all. Indeed, the elders enforce a strict rule that all Tiwi females must marry. As soon as she is born, every young girl is betrothed to one of the elders. The society is polygynous, and the powerful older men betroth their young daughters to other patriarchs. So the older men exchange younger wives with one another, and young men, with no daughters to offer, are thereby excluded from obtaining young partners. If a young man was caught with the young wife of a patriarch, he could be punished severely - by being gored with a hunting spear, or expelled from the group (which in Northern Australia would be tantamount to a death sentence).

So that explains why younger men do not marry women, but why do they marry older widows? That's because all Tiwi females (but not all males) are required to be married. So an older widow must remarry as soon as her husband dies. The powerful older men, who have used the marriage rule to obtain several young wives, are not interested in marrying older women. At this point, a younger man steps up. What's in it for the young guy? By marrying a widow, a young man builds alliances with her relatives, and he gets the right to determine who her younger daughters marry if they become widowed early (remember, all the young girls are also officially married to elderly guys, who may kick off and leave some fertile younger wives as well as the older ones). Once a young man marries a widow, then, he is in the game of acquiring younger wives.

Replacing the Blank Slate with a Coloring Book

The Tiwi pattern demonstrates a dynamic interaction in which new social norms emerge from the combined influences of different evolved psychological mechanisms (men's attraction toward women in the years of peak fertility, women's attraction toward high-status men) and local social factors (a geriatric patriarchy that monopolizes younger women, in combination with a rule that all women must be married).

The Tiwi are one example of why I argue that social scientists' default metaphor for the mind should be a Coloring Book, rather than a Blank Slate. While a Coloring Book can, in one sense, be colored in an infinite number of ways, in not so passively receptive as a Blank Slate, since the outlines in a coloring book strongly suggest (though do not determine) particular palettes of inputs to be used on the different pages. A coloring book is not a Blueprint, in which a predetermined design fixes the outcome. It has blank space between the lines, leaving room for unexpected outcomes: A given child could choose to color his giraffe purple and green instead of tan and brown. But most children coloring a giraffe will be inspired to search for tan, brown, and yellow rather than purple, blue, and green. And there's another benefit of this image -- a Coloring Book gives us an easy to understand metaphor for teaching students about the flexible interactions between evolutionary constraints and local cultural norms. It's as easy to visualize as a Blank Slate, except it's more colorful (and ironically draws a more grown-up picture of the mind).

For further reading:

Kenrick, D.T., Nieuweboer, S., & Buunk, A.P. (2010). Universal mechanisms and cultural diversity: Replacing the blank slate with a coloring book. Pp. 257-271 in M. Schaller, A. Norenzayan, S. Heine, T. Yamagishi, & T. Kameda (eds.) Evolution, culture, and the human mind. NY: Psychology Press.

Kenrick, D.T., & Keefe, R.C. (1992).  Age preferences in mates reflect sex differences in mating strategies.  Behavioral & Brain Sciences, 15, 75- 91.

Kenrick, D.T. (2006). Evolutionary psychology: Resistance is futile. Psychological Inquiry, 17, 102-108.

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