spiders from mars?

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!)


linkfest – 09/29/13

Do Elite ‘Power Sport’ Athletes Have a Genetic Advantage?“A specific gene variant is more frequent among elite athletes in power sports…. A ‘functional polymorphism’ of the angiotensiogen (AGT) gene is two to three times more common in elite power athletes, compared to nonathletes or even elite endurance athletes, according to the new research by Paweł Cięszczyk, PhD, of University of Szczecin, Poland, and colleagues.”

Ballet Dancers’ Brains Adapt to Stop Them Getting in a Spin – or maybe they start off with somewhat different brain structures: “Scientists have discovered differences in the brain structure of ballet dancers that may help them avoid feeling dizzy when they perform pirouettes…. The brain scans revealed differences between the groups in two parts of the brain: an area in the cerebellum where sensory input from the vestibular organs is processed and in the cerebral cortex, which is responsible for the perception of dizziness. The area in the cerebellum was smaller in dancers.”

Math explains history: Simulation accurately captures the evolution of ancient complex societies“The question of how human societies evolve from small groups to the huge, anonymous and complex societies of today has been answered mathematically, accurately matching the historical record on the emergence of complex states in the ancient world. Intense warfare is the evolutionary driver of large complex societies, according to new research….” see also: Math and History Collide. response: No, math cannot predict the rise and fall of empires. (party pooper.)

Genetic study pushes back timeline for first significant human population expansion“Using new genetic tools, the authors conclude that the first significant expansion of human populations appears to be much older than the emergence of farming and herding, dating back to the Paleolithic (60,000-80,000 years ago) rather than Neolithic age (10,000 years ago). They also suggest that strong Paleolithic expansions may have favored the emergence of sedentary farming in some populations during the Neolithic.” – h/t malcolm pollack!

Scientists Created a New Form of Matter and It’s Like a Lightsaber – AWESOME! – see also: Scientists create never-before-seen form of matter

New Approach to Explaining Evolution’s Big Bang“[T]he Cambrian Explosion was preceded by a rise in sea level that submerged vast swaths of land, eroding the drowned rocks…. But these great floods also poisoned the ocean. The erosion of the coastlines released calcium, which can be toxic to cells. In order to survive, animals had to evolve ways to rid themselves of the poison. One solution may have been to pack the calcium into crystals, which eventually evolved into shells, bones, and other hard tissues. Dr. Smith doesn’t think it’s a coincidence that several different lineages of bilaterians evolved hard tissues during the Cambrian explosion, and not sooner.”

No, You Don’t Have Free Will, and This is Why – best post from jayman. ever. (to date! (~_^) ) a response to this.

Robert Ardrey: Incidents in the Disappearance of an Unperson – ok. i’ve run out of ways to say how brilliant helian’s posts are. just go read him already!

The IQ Breaking Point – How Civilized Society is Maintained or Lost“[I]t seems like there is a point, somewhere around 97, above which a modern civilization can be maintained and below which things abruptly begin to fall apart.” – from staffan!

Maths is a man thing* – from dr. james thompson!

Myths about IQ: Episode I – from elijah!

HBD: On Puerto Ricans and Their Heritage, Part I: Before the Taíno – from nelson!

Understanding how infants acquire new words across cultures“[I]n English, 24-month-old infants were better able to learn novel verbs for novel actions (e.g., petting) if the surrounding noun phrases were explicitly mentioned (e.g., ‘The girl is petting the dog’) than if they were dropped from the sentence (e.g., ‘Look. Petting!’). In contrast, the new research shows that in Korean (a language in which noun phrases are typically dropped in conversation) 24-month-olds were better able to learn novel verbs for novel actions if the surrounding noun phrases (e.g., the girl, the dog) were dropped; in fact, unlike English-acquiring infants, those acquiring Korean struggled if the nouns were explicitly mentioned.” – don’t know, unfortunately, what the ethnicities of these infants are.

The Science Fiction Future of Genetic Genealogy“Next month at the American Society of Human Genetics 2013 meeting, researchers from AncestryDNA will present their work detailing the reconstruction of portions of the genomes of an 18th-century couple using detailed genealogical information and Identity-by-Descent (‘IBD’) DNA segments from several hundred descendants of the couple in the AncestryDNA database. In other words, researchers identified several hundred descendants of a certain couple living in the 1700s and then used the DNA shared by those descendants to recreate as much of the couples’ genomes as possible.” – cool! from the genetic genealogist.

Black men have lower sperm counts than white men – @race/history/evolution notes.

Low-Hanging Fruit: Consider the Ant“Some spiders somehow fly by using silken threads. They’ve been detected at altitudes over 4 km, and more than a thousand miles from land. The usual notion is that these threads catch air currents, but that may not be the real explanation. For one thing, they seem to be able to take off fairly rapidly in a dead calm. It looks instead as if these spiders manage to impart a negative charge to these threads and are then propelled upward by the atmospheric electric field – electrostatic levitation, a totally novel mechanism for flight.” – whoa! – from greg cochran.

Brainwashed by a microbe?“*T. gondii* is being studied for possible behavioral effects mainly because it has attracted so much attention. But we’re probably being manipulated by other parasites. ‘A large number of parasitic organisms probably exist in helminths, protozoa, fungi, bacteria, archea and viruses that may influence the phenotype of their human host even more than the Toxoplasma. These organisms are, however, still waiting for research teams to engage in a systematic study of their influence on the human host.'” – from peter frost. previously.

When the Melting Pot Reaches a Boil“If there is one constant in the travails of *Homo sapiens sapiens*, it is that he gets on best with his own kind. Yet to the social engineers who would shepherd us into multicult euphoria, it is as if these millennia of inter-ethnic strife didn’t exist.”

Humans are not the only primates who whisper – so do the cotton-top tamarins. shhhhhh! don’t tell anyone!

What Else Can I Do With My DNA Test Results? – @the genetic genealogist.

That’s not autism: It’s simply a brainy, introverted boy“Autism spectrum diagnoses are up 78 percent in 10 years. We’re dramatically overdiagnosing it in everyday behavior.” – #longread.

The 16 Most (and Least) Honest Cities in the World – wallet test – finns ftw!

Ancient language not heard for 4,000 years is recorded for the first time – PIE (proto-indo-european).

2,500-year-old horse remains found in Bulgaria that suggest the creatures were buried standing up“The carriage and horse skeletons were discovered in the village of Svestari in north-east Bulgaria. They were found in a Thracian tomb along with some decorations.” – cool photos!

How Alcohol Conquered Russia“A history of the country’s struggle with alcoholism, and why the government has done so little about it.” – take note of anatoly’s comments!

bonus: mitual shah – one of the good guys. one of the VERY good guys: Briton died saving children in terror mall“A British marketing executive was shot dead in the Westgate massacre in Kenya after offering himself as a hostage to bargain for the lives of 33 children.”

bonus bonus: I’m sorry, but we have to talk about the barbarism of modern Islamist terrorism – from brendan o’neill.

bonus bonus bonus: hero of the week, via everyone on twitter – After Told He’s Racist, UW-M Student Rejects Further Diversity ‘Training’

bonus bonus bonus bonus: The silence of our friends – the extinction of Christianity in the Middle East – from ed west @the spectator.

bonus bonus bonus bonus bonus: from india – ‘Family honour’ and ‘values’ give immunity to the predator at home – h/t mark weiner!

bonus bonus bonus bonus bonus bonus: The US government has been running a quantum Internet for over two years – cool! – h/t michael anissimov!

bonus bonus bonus bonus bonus bonus bonus: The Demons of Moldova“In Europe’s poorest country, young people are turning to occult religious practices — even exorcisms — to escape everyday life.”

(note: comments do not require an email. cotton-top tamarians!)