Archives for category: evolution

“every society selects for something.” — greg cochran

every society selects for something. it does take some time for selection pressures to make a difference when it comes to the frequencies of “genes for” various behavioral traits, of course (unless the culling is extreme): twenty generations, maybe. forty is probably better. a few hundred? yeah, that’ll definitely do it. the point is, it doesn’t necessarily take millions of years for evolution by natural selection to work. not even tens of thousands. we don’t have to cast the net back to the paleolithic or even the mesolithic in our search for the origins of behavioral traits in human populations (although the roots for many of them are probably there…or even farther back to our common origin with other apes and even other social mammals, lizards, fruit flies, tomatoes etc., etc.) — we can and should look for selection pressures in more recent eras, too. and “the environment” that exerts these pressures on human populations is not just the natural world — it’s our social worlds, too.

this will be the first in a series of posts on manorialism in medieval europe, because i think that it’s incumbent upon every blogger to bore their readers to tears medieval society in northern europe (ca. 400-1500 a.d.) produced some quite unique selection pressures which very much shaped the characteristics and personalities of “core” europeans, i.e. the dutch (minus the frisians), the belgians, the french (especially the northeastern french), the english (especially the southeastern english), to some degree the lowland scots, the germans (especially those to the west), the scandinavians (especially those further south), the northern italians (especially those from the north italian plain), the northern spanish (especially catalonians), and to some degree the swiss. one of those selection pressures was, of course, europe’s Outbreeding Project, which i never shut up about. (sorry!) the other big one, i think, was manorialism — a communal agricultural system that was really an almost all-encompassing socio-religious-political system which, although its features and importance did vary at different times and in different locales, pretty much regulated nearly all aspects of medieval europeans’ lives. where it existed — a key point which i’ll come back to later.

the working theory around here is that the Outbreeding Project set up the selection pressures for getting rid of much of what we could call “nepotistic altruism” in core europe, allowing for greater cooperation and trust between unrelated individuals and, therefore, a more open and “corporate” sort of society. a second working theory is that manorialism set up selection pressures for a whole suite of traits including perhaps: slow life histories; future time orientation; delayed gratification; the good ol’ protestant work ethic; a general compliant nature and even rather strong tendencies toward conformity; perhaps even a high degree of gullibility; perhaps a few extra iq points; and even more cooperation and trust between unrelated individuals. or not. please keep in mind that i’m just thinking out loud in these posts. oh — the manor system also probably contributed to the selection for the reduction in impulsive violence. (i’ll be exploring more fully the various aspects of manorialism that i think may have created the selection pressures for these various traits in the coming posts — promise! just giving you a rough outline now.) the Outbreeding Project and manorialism very much went hand-in-hand as well — the medieval european manor system could not have happened without all of the outbreeding, and the Outbreeding Project was reinforced by the manor system (since marriage was often regulated within the manor system).
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manorialism — “classic,” bipartite manorialism (more on that below) — started with the franks in austrasia by at least the 600s or perhaps earlier and spread gradually southwards with the frankish conquest of, well, france and eastwards during the ostsiedlung. we find it just across the channel in southern england very early as well — there are references to what sounds like features of a manor system in the laws of king ine of wessex (688-726) [see mitterauer, pg. 43]. the medieval european manor system originated, then, roughly in the area outlined in green below (yes — this is the very same area where the Outbreeding Project began. which is convenient, really, ’cause i like not having to make multiple maps! in case you’re new here, the other lines on the map indicate the hajnal line.):

hajnal line - core europe

interestingly, the frisians, although quite centrally located on the coast of the netherlands in this core region, never experienced manorialism. mitterauer ties manorialism to cereal agriculture and the new agricultural techniques developed in the early medieval period (with the introduction of the heavy plow, etc.), so areas unsuitable for such farming — like mountainous regions or swampy areas — typically simply did not see the introduction of the classic manor system.

classic manorialism was introduced to southern france (but bypassed some more remote areas like the massif central) as those regions were conquered by the merovingians and carolingians between the fifth and eighth centuries and to northern spain around the eighth and ninth centuries. the bipartite manor system never reached the southern regions of spain that were controlled by the moors. there was a rudimentary form of manorialism in northern italy even before the area was made a part of the carolingian empire, but the region was heavily manorialized (especially by ecclesiastical monasteries) after charlemagne conquered the lombard kingdom in the 770s. classic, bipartite manorialism was never adopted in central or southern italy or sicily — nowhere in the byzantine world, in fact.

the franks also pushed eastwards, introducing the manor system to central europe, beginning in the eighth century. the border of this eastward movement was, for a couple hundred years or so, the eastern boundary of the carolingian empire (look familiar?). a renewed push eastwards began in the eleventh and twelfth centuries, and a slightly revised form of classic manorialism (a system based upon rents rather than work exchange) was introduced to areas/populations further to the east in central-/eastern-europe including the baltics, large parts of poland, bohemia, moravia, parts of slovakia, western hungary, and slovenia. quite obviously, these populations experienced manorialism for a shorter time than those to the west.

the “classic” form of manorialism never reached the farthest parts of eastern europe. eventually, a form of manorialism was adopted in russia and areas of eastern europe bordering russia, but it was quite different than the version western europe had had. this serfdom-heavy manor system in eastern europe also arrived very late compared to manorialism in western europe — in the fifteenth century (iirc) or in some areas even much later. classic manorialism had practically disappeared in western europe by this point.

in scandinavia, denmark was heavily manorialized relatively early i believe (probably around the time of the first wave of the ostsiedlung, although i must check the dates), and manorialism was also very much present southern sweden (scania). the more northerly parts of scandinavia — norway, northern sweden (or sweden north of scania), the swedish-settled areas of finland — didn’t have manors per se, but were covered by a unique version of “manorialism” in which much of the population was under the thumb of the church (and sometimes petty aristocratic landowners). i know my nordic readers are going to object to me saying that, but please wait for the post on manorialism in scandinavia before bombarding me with your counterarguments. thanks! (^_^) this unique form of “manorialism” arrived in northern scandinavia rather late — probably in something like the 1200s (i need to check on that date) — and departed late (the 1800s and even the 1900s in some areas). not sure what happened in the areas of finland not settled by swedes. and i’m pretty sure no form of manorialism ever took hold in iceland, although i reserve the right to be wrong about that. (~_^)

classic manorialism arrived late in ireland — in the late 1200s — and was introduced by the anglo-normans. there was never really much manorialism in wales or the highlands of scotland, although kind david did introduce it to the lowlands of scotland in the 1100s. not sure how well it took hold there, though. i’ll let you know as soon as i do. proper classic manorialism wasn’t really found in cornwall, either, and manors were not very prevalent in east anglia, although there were some.

there was never any manorialism in the balkans.

nor was there ever any classic, bipartite, european-style manorialism in the arabized, islamic world or in china, although there were plenty of large estates in china throughout its history. (don’t know about japan or the korean peninsula.) the difference between medieval european manors and the manors of china has been characterized as a difference between manorialism — which was a sort-of communal agricultural system in which everyone who worked on the manor was a part of a familia — and landlordism, which is what you had in china [pgs. 11-12]:

“In two major works in particular (Hu Rulei 1979; Fu Zhufu 1980), we find sustained analyses of the differences between the socioeconomic structure of imperial China and that of the precapitalist West…. For Hu Rulei, the key lies in the differences between Chinese ‘feudal landlordism’ (*fengjian dizhuzhi*) and European ‘feudal manorialism’ (*fengjian lingzhuzhi*). In the European feudal manor, landownership or economic power was merged with military, administrative, and judicial powers; each manorial lord exercised the entire range of those powers. The state system of manorialism was thus one in which sovereignty was parceled out. In Chinese landlordism, by contrast, political authority came to be separated from economic power through private land-ownership and the frequent buying and selling of land. This made possible the centralized imperial state system. Landlordism and the centralized imperial state thus made up an interdependent politicoeconomic system that must be distinguished from European manorialism. Hu’s is an analytical model that can help explain the differences and hence also their different paths of sociopolitical change in the modern era.

“Fu Zhufu has pointed to another difference between manorialism and landlordism. In the serf-based manorial system, the lord had to look to the subsistence and reproduction of his workers, lest the very basis of the manorial economy be undermined. But the Chinese landlord was under no such constraints. He could seek the highest possible returns that the land-rental market would support (Fu 1980: 9-10, 201-2). Though Fu skirts the issue here, it is obvious that such principles became harshest when the pressures of social stratification were joined by the pressures of population; under those conditions, a tenant who failed to survive could always be replaced by another. Landlordism could become an institutional system in which the poor tenants were pressed below the margins of subsistence.”
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which brings me, now, to some of the various characteristics of classic manorialism and the selection pressures that i think they may have exerted.

– the bipartite estate. the bipartite estate was a key aspect of classical (north)western european manorialism. basically, the manor was divided into two parts: the lord’s part — his farm or demesne — and the peasants’ or serfs’ parts — all their individual farms. the serfs or villeins or whatever you want to call them (there were multiple categories of these peasant farmers and a range of names for them) each had farms to work which were granted to them by the lords (keep in mind that sometimes those “lords” were bishops or monks who ran the monasteries). in the earlier part of the medieval period, the serfs owed labor to the lord of the manor as payment — they were obliged to help work the lord’s demesne — but they also independently worked the farms which they were granted, both to sustain themselves and perhaps make a little profit by selling any extra produce to the neighbors or in a market. there were other obligations, too, but the above was the fundamental gist of the whole system. later in the medieval period, the duty to provide labor switched over to a more simple and direct rent system.

also early on in the period, serfs were given (or assigned) farms to work by the lord of the manor. as a young man, you might not be given the same farm that you grew up on — that your parents had worked — especially not if your father/parents were still productive workers. the lord of the manor, or his steward, would just grant you another farm on the manor to work…if there was one available…and if he chose to do so (presumably based on your merit or your familiy’s record). this system eventually changed as well into one in which a son (typically the eldest son) would “inherit” the farm that his father/parents had worked. not sure when this happened. must find out.

not everyone who was a member of a manor operation would be granted a farm to run. some individuals were just laborers on the manor (“cottagers” in england, for example), and there were plenty of domestic servants serving in the manor house, too.

i think that there are potentially selection pressures here for several different traits or qualities. if we ask ourselves, what sort of individual would’ve done best living in this bipartite estate system, i.e. which individuals with which sorts of traits would’ve managed to reproduce the most, i think it might’ve been people with qualities including: being hard-working or industrious — those that made the most of the farm grant and produced the most food to support the most number of kids and even to sell extra produce for a profit; perhaps smarter than some of the neighbors (like the cottagers) — for the same reasons as hard-working; future time oriented — you had to be patient and wait for a farm to become available, or later in the period wait for your father to hand over the farm or die, and not start philandering about the manor before you could afford to raise kids (you also might not be granted a farm, or acquire yourself a husband, if your reputation was ruined beforehand); slow life histories — those individuals who could hold off on reproducing too early would’ve been rewarded with farms, those that did not would’ve been shunned and would lose the opportunity to reproduce further; and compliancy — you didn’t rail (too much) against the man in the manor, and anyone that did wouldn’t have gotten a farm and may have, if they caused too much trouble, been shipped off to a monastery for life (more on that in a later post).

– villikation and familia. villikation is the term that german researchers use when referring to the fact that the manor and all its inhabitants/workers were managed by someone, either by the lord of the manor himself or by a steward who the lord had put in charge of running the place. you would think that, as a serf or tenant farmer on a manor, you wouldn’t want to run afoul of whoever was in charge, and very often those that did were shipped off the manor (to monasteries), so it seems to me that there might’ve been further pressures here to select for compliant and cooperative individuals.

familia was the word used for everyone who was a member of a particular manor! it was a term used especially earlier in the medieval period, but i think it was in usage throughout the entire era (need to double-check that). from mitterauer [pg. 57]:

“On the one hand, there was the villa, the lord’s manor, or the stewards’ manor, with its resident labor force, the members of which were not tied to one another by kinship; on the other hand, there were the farms of the *servi casati*, that is, of the unfree laborers and their dwellings, as well as the *coloni* who were bound to the soil and therefore to a house. Together they formed the *familia*, an overarching household embracing several households.”

a classic (north)western european manor, then, almost sounds like a 1960s hippie kibbutz, at least when it came to the relatedness of the individuals on the estate. (unlike a hippie kibbutz, though, The Man was clearly in charge.) the people living and working on a medieval manor in (north)western europe were not all members of one extended family or clan (which you do see elsewhere, like in eastern europe, especially russia, or southern china). this system, along with the Outbreeding Project, might’ve encouraged the selection for individuals who were willing to cooperate with other (comparatively speaking) unrelated persons. it might even have helped, along with the Outbreeding Project which got rid of much nepotistic altruism imho, to select for highly trusting — and quite highly trustworthy — individuals.

– open-field system. another key feature of (north)western european manorialism was the open-field system in which shares of large “fields” were apportioned out to each family on the manor — each household would get a long strip or strips within one of these huge fields in which to grow their crops. open-field systems were used by the pre-christian germans and slavic populations (iirc), but in those contexts, extended family/kindred/clan members typically shared the fields. again, in the classic manor system, we have more unrelated individuals/families sharing these fields. residents of the manor regularly policed one another, bringing each other to the manorial court if they thought someone was cheating in the open-field system (and also in the usage of the commons), so, again, here we might have the selection for cooperative and trustworthy individuals.

– ecclesiastical manors. i think the presence (or absence) of ecclesiastical manors in any given area might be very important. apparently, ecclesiastical manors exercised more control on their residents, and until later in the period, than those headed by lay lords (more on this in a later post). so, i’d expect all of the behavioral traits associated with manorialism to be even more pronounced in areas/populations that had more than their fair share of ecclesiastical manors: south-central england, france, germany, and northern italy (and northern scandinavia?).

again, these are all just some ideas. Further Research is RequiredTM! would be cool if someone looked through some manor records to see if they could find out which, if any, class of peasants/serfs managed to reproduce more successfully. maybe someone already has?

if/when the “genes for” any or all of the behavioral traits i’ve mentioned here in this post are discovered, my prediction is that the frequencies for them in european populations will be highest in those in the core area and, thanks to the historical origins and spread of manorialism (and the Outbreeding Project), that these frequencies will reduce with distance from that core. again, i reserve the right to be completely and utterly wrong about that. (~_^)

that’s it for now. stay tuned for a bunch of posts on medieval manorialism in the coming weeks! but first, some other business….
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previously: big summary post on the hajnal line and medieval manoralism and the hajnal line and behind the hajnal line and medieval manorialism and selection…again und die ostsiedlung

(note: comments do not require an email. a french manor: chateau de montargis)

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there were a handful of science news stories out this past week about how a couple of researchers reportedly discovered a case of “group selection” in certain spiders (Anelosimus studiosus or tangle web spiders): for example, see Proving ‘group selection’: Spider colonies need the correct mix of personalities to survive and Elusive Form of Evolution Seen in Spiders. a bunch of people on twitter got all excited about this finding, because they wonder if (some of them i think hope that) group selection might also apply to groups of humans. i agree: that would be very interesting to know one way or the other. so i went and read the original paper — Site-specific group selection drives locally adapted group compositions — to see what these guys had found.

before i offer up my admittedly layman’s thoughts on this paper, let me first say what a really neat piece of research this was! if there existed a nobel prize for geeky dedication and sheer nerdiness, these guys would’ve won it! — and i mean that as a compliment! the researchers, pruitt and goodnight, studied groups of tangle web spiders in the wild, captured some and brought them back to their lab, conducted personality tests on the spiders (yes! there are apparently personality tests for spiders!), painstakingly painted those little dots on the backs of individuals to keep track of them (you know, like how they sometimes do with bees), bred the spiders, released new groups of them back into the wild, and checked up on them one and two generations later to see how they fared. this is some really cool research! nerds ftw! (^_^)

but did they find evidence for group selection?

weeeellll, no, i don’t think so.

to begin with, right at the start of the paper pruitt and goodnight (p&g) define group selection as “selection caused by the differential extinction or proliferation of groups.” eeeehhhh, as far as i understand it, that’s not really the definition of group selection, and even the authors admit that their definition is a “broad” one.

group selection is more accurately defined as when “natural selection [operates] between groups of organisms, rather than between individuals.” in contrast, p&g’s broad definition could theoretically include cases in which natural selection worked between individuals (individual selection) which also just incidentally happened to result in the proliferation of the group to which the lucky selected individuals belonged. an example of this is the selection for lactase persistence in some humans in which those individuals who could drink milk as adults were able to leave behind more descendants than those individuals who could not. while lactase persistence might indeed have benefitted groups of milk-drinking individuals, natural selection did not act on the group, but rather on the individuals in that group. (pretty sure i stole this example from @supermisdreavus, but i can’t find where he said that right now.)

in other words, you always need to work out what the target of selection is: the group or the individuals that make up the group. (really it’s ultimately the genes, but — oh, nevermind.) remember that “‘a fleet herd of deer’ is really just a herd of fleet deer.”

so, really, the discussion could end right here, because i don’t think the authors are talking about group selection proper. but, since i’ve read the whole paper, i’ll carry on. (yes, i’m one of those people who’s never learned to quit while they’re ahead!)

a. studiosus spiders live either as solitary individuals or in groups where they cooperate on tasks like hunting and the raising of young. the individuals that live together in groups are, on average, more closely related to one another than those that live alone [pdf] — they’re generally as related to one another as though they were half-siblings. one reason why they’re probably not more related to one another in these groups — like to the degree that ants or bees in colonies often are — is that the males move between groups. remember that.

the personality types of the individual spiders in a. studiosus groups come in two sorts: docile and aggressive. the docile spiders are typically pretty laid back and aren’t much bothered by the presence of other spiders (even spiders from other species), whereas the aggressive individuals like their space — they’ll chase off other individuals. individuals of both types are found in groups of a. studiosus, but the frequencies vary. from the paper:

“At…high-resource sites, small colonies were dominated by docile females and the frequency of aggressive individuals increased with colony size. By contrast, at low-resources sites, small colonies were dominated by the aggressive phenotype and the frequency of the docile phenotype increased with colony size.”

well, that doesn’t sound too surprising at all. in locales where there is plenty of resources, there are more laid back individuals in the colonies, prolly ’cause being laid back works just fine. in areas where resources are lacking, more aggressive individuals do better. btw, they found that the heritability of these personality types in the spiders is 0.66.

groups that have more docile individuals (i.e. the ones in high-resource areas) are at a greater risk of invasion by other types of spiders which, over the long-term, tends to be a really bad thing for an a. studiosus colony (i.e. it’s usually destroyed). groups that have more aggressive individuals (i.e. the ones in low-resource areas) tend in bad times to experience too much “egg case cannibalism.” needless to say, that’s not a good thing over the long-term either.

what p&g did in their study was to introduce into the wild — into differing environments — groups having varying frequencies of these personality types [source]:

“He [pruitt] took spiders from warrior-heavy colonies and used them to assemble new groups that were heavy on the nannies. He also used spiders from mostly docile colonies to create warrior-laden groups. In addition, he assembled control groups that matched the composition of their original groups.”

what they found was that after three generations:

“60 percent of the colonies were extinct. Control groups that returned to their ancestral homes tended to do well, and those that were transplanted into a new environment generally died. Neither of these outcomes was much of a surprise.

The most interesting results came from colonies made up of spiders that had been forced into a composition different from the one they grew up in — warrior-majority colonies containing spiders from mostly docile groups, for example. The colonies whose composition fit the new environment tended to survive. But over time, surviving colonies reverted to their members’ original group composition. The warrior-majority colonies went back to having more nannies, for example. On the face of it, this is bizarre behavior; if the colonies are well-suited to their environment, why not maintain that ratio? It seems that some innate sense, perhaps encoded in the spiders’ genes, pulled the colony back to its original configuration, even though this change meant the colony would perish.”

well, i dunno. is that really “bizarre behavior?” i mean, if the personality types of a. studiosus are really highly heritable (0.66), is it strange that a population having come from a bunch of docile individuals should regress toward a docile mean? and vice versa? don’t forget, too, that the individuals in these groups are all related to one another as though they were half-siblings, so presumably individuals of either personality type might carry a great many genes of the other type in their genomes. (don’t know about that — i’m just guessing here, tbh.)

what really made me question whether or not this is “bizarre behavior” is the way in which the researchers bred the spiders when they had them in captivity [from the methods section at the end of the paper]:

“Females were mated randomly to a male of like behaviour type from their same source population, but which was collected from a source colony >5m distance.”

hmmmm. i dunno about that. they mated all the females with males of the same personality types, docile or aggressive? i’m guessing that they did this in order to reduce the number of possible confounding factors in the study, but i’m afraid they might’ve added something to the mix here that wouldn’t be found in nature, i.e. a 100% assortative mating rate (for personality type). mightn’t this almost guarantee that individual spider lineages would regress to their original personality-type means? docile females always mated with docile males and aggressive females always mated with aggressive males? that seems unlikely to happen in nature, especially given the fact that the males normally leave their colonies and move to others. (btw, male a. studiosus spiders prefer moving into colonies over mating with lone females. typical males, favoring harems! (~_^) )

p&g offer a number of explanations for how the frequencies of personalities in the groups might change over time:

“How native spiders are actually able to adjust their composition is unknown, but plausible regulatory mechanisms include developmental plasticity in the docile:aggressive phenotypes, policing of group membership, phenotype-biased dispersal, and/or selective cessation of reproduction.”

they reject the first explanation (the plasticity one) on the basis (in part) of the rather high heritability of spider personality types which they found. i’m inclined to agree with them on that.

out of their other reasons, policing of group membership and selective cessation of reproduction are behaviors that can be easily explained by natural selection between individuals, especially in populations that have rather highly related individuals so that levels of altruism are pretty high. the selective cessation of reproduction occurs, for instance, in some ant colonies since, due to the really high degrees of relatedness between individuals, the inclusive fitness payoffs are really large (eg. if you share three-quarters of your dna with your sister’s offspring, there’ll be a greater genetic payoff in helping her to reproduce rather than reproducing yourself, since you’d only share half of your genome with your offspring). that’s individual selection, not group selection. h*ck! both behaviors also occur in meerkat groups, although they, of course, show much less specialization of individuals than ants or bees. the policing of group membership can also be plausibly explained by natural selection between individuals — for example, aggressive individuals keep at bay all sorts individuals because that’s good for aggressive individuals (who are typically found in sparse environments).

so, i’m not at all convinced that pruitt and goodnight have found an example of group selection. i think they’ve found that genetics (as indicated by the heritability of the spiders’ personality traits) and natural selection certainly shape the average characteristics of groups, but it looks to me as though the seemingly “bizarre behaviors” that they found can easily be explained by individual selection. in fact, i’m more than a little concerned that due to the way they bred the spiders, p&g may have affected the outcomes of the reintroduced groups.

see also: The False Allure of Group Selection from steven pinker.

(note: comments do not require an email. a. studiosus group web!)