leaving the nest

this from pew popped up on twitter a couple of weeks ago (and again earlier this week)…

…and several people, unprompted by me (and who are not even in my pay — i swear!), noted that it all looks very hajnalliney.

well, yes!

just in case you can’t draw mental hajnal lines automatically yet (and you really ought to work on that if you can’t), here it is:

john hajnal didn’t actually have anything to say about average ages of leaving home in european populations, but his line and when young european adults leave the nest do correlate strongly. this has been studied quite extensively (don’t just take my word on it — see david rehr, for instance), and the pattern extends back pretty far in time. from peter laslett’s Characteristics of the Western European Family:

“This self-deception about the history of the family has particularly affected Western Europeans. Frenchmen, Germans or Englishmen, unless they have come across the work of recent historical sociologists, are likely to believe the following. That the co-resident familial group in the past, at least up to the point of industrialisation, was large and complicated, with several generations living together. Furthermore, that this comfortable, kin-enfolding, welfare-providing family group not only nurtured the young, but took in their spouses when they married, and also provided them with shelter and succour when they became old or suffered other misfortunes. That the family in the sense of extended kin was a further source of welfare. It seems to be supposed that before the days of the Welfare State it was the family and kin which rescued social casualties. Now all this has turned out to be untrue.

“Untrue, that is to say, in a literal sense and for the particular part of Western Europe which first became industrialised and which has given what might be called industrial culture to the rest of the world. By this North-West Europe, especially the British Isles, Northern France, the Low Countries and Scandinavia, is meant. In this cultural region family groups had been simple in composition and quite modest in size for many centuries before industrialisation. Married children only seldom lived with their parents, and two couples in one family household were quite unusual. It is true that the family group has become much smaller in the 20th century, servants have disappeared, and solitary living has grown enormously in our own day: but this did not happen during the process of industrialisation as ‘traditional society’ gave way to ‘modern society’ and cannot be called a transition to the ‘nuclear family’. The ‘nuclear family’ was there already.

“The kin composition of the English family group was much as it is today in the 16th century, and had been so since the 1300s, the 1200s or even earlier…”

probably even earlier. the nuclear family was a feature of bipartite manorialism and is documented in carolingian france as early as the 800s [see mitterauer, pgs. 62+]. bipartite manorialism was invented in austrasia in the 500s, but arrived across the channel not long afterwards. throughout the medieval period, manorialism was strongest in the southern and central parts of england, so chances are the nuclear family has been around the longest in those areas of the country, while the extended family remained of greater importance in other, peripheral regions (not to mention wales and scotland). this was definitely the case for east anglia.

back to laslett and average ages for leaving the nest (he’ll get to it eventually):

“…but with one very imortant structural difference. Servants lived in large numbers of families, and the presence of servants made the family groups of the rich large, and the family groups of the poor correspondingly small. In this area of the West, moreover, welfare never flowed along lines of kinship. The casualties of the system, the widows, the orphans, the poverty-stricken, were supported by the collectivity rather than the family.”

“The family structure I have just described was at its most homogeneous in England and the Low Countries, was less so in Germany and in Central Europe, and much less so in Southern Europe. France, indeed, seems to have been divided. Languedoc had larger and more complex households, especially in the mountains, than the rest of France. In spite of this important fact, the development of the Western European family can no longer be seen in the particular way which has been fashionable for the last generation, not even in areas where complicated family households have been common – areas like the Pyrenees, the Massif Central, or, which is very surprising, Tuscany and other parts of Italy.

“It is a mistake to think that the transition in family matters which is now going on in the developing societies of the contemporary world repeats the earlier history of the Western European family. Nevertheless, if we take Europe as a whole, and not simply our Northern and Western area of it, we are faced with the recent discovery that in Russia things were very different. Among the serfs before they were given their freedom in the 1860s, the family was large and complicated, more so than for any other example of complicated families which has yet been found anywhere in the world, in the past or in the present. The fact is that, within the continent of historic Europe as a whole, family forms varied as widely as it is possible to do. This not withstanding the circumstance that in Britain and in other parts of North-Western Europe they were uniformly small and simple….

“Characteristic 6 is the existence of large numbers of life-cycle servants: younger men and women spending the period between puberty and marriage as resident employees and members of the family of other persons, usually more substantial than their parents….”

life-cycle servants are well-documented from the 1300-1400s and onwards in england (and elsewhere in northwestern europe), but, again, this quirky system has its roots back in bipartite manorialism and can be seen in the records of carolingian period manors in northern france. from mitterauer [pgs. 64-65]:

“Life-cycle servants were people in the household who were different from the domestic slaves found in many cultures, and they were sometimes included among members of the family…. As a matter of fact, these domestics were often found in property registers as early as the Carolingian period. We cannot determine whether or not the servants mentioned in these sources were adolescents because no ages were given, but this was probably the case, since they were all single….

“Working as a servant was correlated with marriage at an advanced age. Until you could marry, you were kept in a dependent position that was essentially a child’s role — if not at your parents’ house then living as a farmhand or maid with a family unrelated to you.””

so kids in northwestern europe have been leaving home at an earlier age on average than those in southern or eastern europe for probably something like one thousand years. and this difference is tied to the historical distribution of bipartite manorialism in medieval europe.
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“But the Western European institution of life-cycle service has its surprises and its puzzles too. An outstanding feature of these very large numbers of young people in service was that they moved from one household to another almost every year. The faithful and trusty retainer is one more of the literary myths about European family structure – myths in the sense of substituting the entirely exceptional circumstance for the wholly normal, as in the case of Juliet’s marriage.”

previously: viscous populations and the selection for altruistic behaviors and big summary post on the hajnal line

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recognizing your un-kin

if you want to be un-altruistic toward some un-kin of yours, it might be useful if you could spot who they are.

here’s some neat research [pdf] suggesting that perhaps we can do just that (further research is required, of course). this is one of those manipulated photographs studies — you know — where they take photos and alter them to look more or less like the subjects. note that the study was done on w.e.i.r.d. students — and way more females (n=112) than males (n=32):

“Kin recognition: evidence that humans can perceive both positive and negative relatedness” (2012)

“… The evolution of spite would have been greatly facilitated by the ability to recognize negative relatives (West & Gardner, 2010). The current study is the first to find such an ability among humans, one of only a handful of species (Keller & Ross, 1998; Giron & Strand, 2004) for which there is evidence of negative relatedness recognition, by introducing a novel cue to negative relatedness (negative self-resemblance). Specifically, we found opposing effects of positive and negative self-resemblance – cues to positive and negative relatedness, respectively – on trusting and attractiveness attributions, as predicted. This result provides a foothold for the possibility of the evolution of spiteful behaviour among humans. Future research should examine this possibility.

“Although the effects of positive and negative self resemblance in our study were generally small, our study was an experimental one. Thus, we controlled the strength of the manipulation. It was our intention to make the stimuli subtle, to ensure that the participants would not discover the nature of the manipulation. A subtle manipulation, however, will tend to lead to subtle effects. What we hoped to show was not that the positive and negative self-resemblance manipulations had large effects on preferences or behaviour in the context of a laboratory experiment, but that they had predictable effects at all, especially as these effects speak to theory (Prentice & Miller, 1992).

“Relative to matched participants, focal participants generally had positive preferences for their own positive self-resembling faces but negative preferences for their own negative self-resembling faces across contexts….“

here’s the relevant graphic:

“Spite is hypothesized to evolve under relatively restrictive conditions (West & Gardner, 2010), and so it is expected to be rare. However, two conditions may, together, favour its evolution: (1) ‘viscous’ breeding systems and (2) the ability to recognize negative relatives. Population viscosity can make competition increasingly local among individuals (Taylor, 1992a,b), and local competition encourages the evolution of spite (Gardner & West, 2004). Furthermore, individuals immigrating into a viscous population may be strongly negatively related to members of the indigenous population, because immigrants are highly unlikely to bear the same (relevant) alleles as indigenous individuals (Krupp et al., 2011).”

for “viscous breeding systems” i think we can safely insert “inbreeding” or “cousin marriage” or “consanguineous matings.” they are all certainly viscous.

“Negative relatedness recognition can improve the targeting of a spiteful action to increase indirect fitness benefits (by delivering harm specifically to negative relatives whilst sparing positive ones), and our results provide evidence that humans have the mechanisms in place to do precisely this. Moreover, countless animal species use phenotype matching to determine relatedness, and other kin recognition systems exist that might also be employed to discriminate against negative relatives (reviewed in Krupp et al., 2011). Further discoveries that organisms have the capacity to recognize negative relatives will lay a foundation for the study of spiteful behaviour, arguably the last great unexplored problem of social evolution….”
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what i’d like to see is some research done on actual inbred populations. maybe a comparison between a non-inbreeding population and an inbreeding one to see if either of the two groups is better at spotting their kin or un-kin.

for that matter, i wonder if kin in inbred populations actually look more like one another than kin in outbred populations (and, therefore, look more unlike non-kin). you would think they ought to since they share more of the same genes with one another. you’d think that’d affect appearance, too. remember the ghoul brothers from syria (click on picture for LARGER view)?:

redzengenoist said about them: “It really is striking how much they look like one another. Far more than I would expect the average family group to have similar appearance…. I’m thinking of selection for markedness of ingroup-ness. I can’t help but wonder if having a distinct ‘look’ helps to facilitate the evolutionary advantages of inbreeding….”

i noted: “and, like the big families i’ve known (from my slightly inbred area of the world), some of them look more like each other than they do to the others. the two (chubby guys, roundish faces) on the right and the guy all the way on the left look similar — those three look like mom? or dad? and the other five look more like each other — like the other parent (whichever one).”

maybe it’s easier to spot kin and non-kin in a “viscous” population. the more viscous the better, perhaps.

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