For a Good Time, Well, Don't Call Dad

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December 2, 2003
For a Good Time, Well, Don't Call Dad
By MARY DUENWALD

Sir Walter Scott was an author, not an evolutionary theorist. He wrote his poems and historical novels 40 years before Charles Darwin described the process of evolution -- and well over a century before scientists began in earnest to apply principles of natural selection to the study of human nature.

Yet Scott, a 19th-century writer, apparently shared with modern evolutionary scientists the general notion that men tend to follow two basic mating strategies.

The new research is part of the fledgling field of Darwinian literary studies, in which scholars try to draw connections between literature and evolutionary science.

According to a new study, Scott's dark heroes, rebellious and promiscuous, and his proper heroes, law-abiding and monogamous, reflect the two types of men scientists recognize by the kinds of relationships they have with women: cads and dads.

In the study, 257 women in college were asked to read passages from Scott's novels. Each read a paragraph describing a dark hero and one describing a proper hero. Then the women were asked which type of man they would prefer for a relationship.

As predicted by the cad-dad theory of human mating strategies, the women preferred the proper heroes for long-term unions. When asked which character they would like to see their future daughters choose, they also selected proper heroes. But when asked who appealed to them most for short-term affairs, the women turned to the dark heroes -- the handsome, passionate and daring cads.

''These 21st-century female college students could understand mating strategies intuitively,'' even when they were described in dated language, said Dr. Daniel J. Kruger, a social psychologist at the University of Michigan's Institute for Social Research, who led the study. It is published in the fall 2003 issue of the journal Human Nature.

Finding a dichotomy between the two male types in Romantic novels two centuries old informs both evolutionary science and literary studies, Dr. Kruger said. It demonstrates that the distinction between long-term and short-term mating strategies is instinctive, and it gives literary scholars a new way of examining old writings.

Men and women, playing off each other, use long- and short-term thinking, and sometimes a mixture, in picking partners, Dr. Kruger said. Women recognize the kind of men who pursue short-term affairs, he said. They fit the description of George Staunton in Scott's ''The Heart of Midlothian,'' who is handsome, daring and ''unconstrained,'' and who displays ''the abrupt demeanor, the occasionally harsh, yet studiously subdued tone of voice.'' Such dark heroes in Romantic literature, Dr. Kruger said, are typically single and promiscuous.

The title character of ''Waverley'' illustrates the dad. Waverley is in the army but shows little interest in adventure. One friend says of him, ''I will tell you where he will be at home and in his place -- in the quiet circle of domestic happiness, lettered indolence and elegant enjoyments of his family's estate.'' These proper heroes are typically kind and altruistic and prone to tender emotions, like love and melancholy.

Cad and dad strategies are both adaptive, from an evolutionary perspective, Dr. Kruger said. The cad approach enables a man to father many children, while the dad approach ensures the children a man has will thrive.

Women get an obvious payoff from pursuing a long-term relationship: help in rearing children. But they also benefit from brief flings, said Patricia Draper, a professor of anthropology at the University of Nebraska who in the 1980's was among the early scientists to describe the cad-dad split. Women may not be as free as men to opt out of their parental duties, but they still can have more than one sexual partner, Ms. Draper said, and that allows them to mix genes with sexually appealing cads.

''In some societies where there is little male investment in parenting, a women's best strategy may be to find the biggest, toughest, most attractive fellow out there,'' Ms. Draper said. That way, a woman may end up with a ''sexy son'' who, in turn, will successfully mate and have children.

Women may also gain material advantages from short-term relationships, said Dr. Henry Harpending, an anthropologist at the University of Utah who has written papers on the topic with Ms. Draper. ''The sexy son notion is plausible,'' he said, ''but what females may also get from a short-term affair is a new pair of shoes.''

That both men and women have the inclination to engage in short-term flings indicates how adaptive the behavior is, Ms. Draper said, because men and women are very sensitive to infidelity. ''Men kill women who are unfaithful,'' Ms. Draper said. And, she said, ''women are sometimes driven to murderous rage, too,'' citing the Greek tragedy of Medea, who becomes enraged at Jason's infidelity and slaughters their children.

Evolutionary theorists see parallels between the human situation and that of other species, when the male and female parents take care of the offspring. Female warblers, robins and bluebirds, for example, engage in what scientists call ''extra-pair copulations,'' so that in many cases the nestlings' biological fathers are not the mothers' parent partners, said Dr. David Barash, a zoologist at the University of Washington who has studied the mating behavior of mountain bluebirds.

Some evidence suggests that when female birds engage in extra-pair copulations, their choice of male is based on the bird's sexual attractiveness, Dr. Barash said. Female bluethroats, a Eurasian species, for example, will have sex with males whose throats are an especially iridescent shade of blue. And female barn swallows are drawn to males whose tail feathers are deeply forked.

Those barn swallows with appealing tail cleavage also tend to be less attentive as fathers than other males, Dr. Barash said. ''The payoff, to a female, of producing sexy sons, via a cad, makes up for the cost of being stuck with a comparatively deadbeat dad,'' he said.

Such females, if they are found out, pay a high price for their infidelity, Dr. Barash said. ''If a male bird encounters his female in close proximity to another male at the time of breeding, almost inevitably what happens is that the male stops paying child support, essentially. He'll stop investing in the offspring,'' Dr. Barash said.

But if they can get away with it, these females gain the advantage of mixing their genes with those of highly adaptive males, he said. ''The optimum reproductive strategy for females seems to have been and still is to mate with a male who will invest in your offspring, but keep your eyes open for one whose genes will interact well with your own,'' Dr. Barash said.

The concept of short-term and long-term mating strategies in humans is nothing new, as 19th-century literature attests.

''Bodice rippers, for centuries, have made a profit off this sort of distinction,'' said Dr. Marlene Zuk, a biology professor at the University of California at Riverside. ''Nice guys have been complaining that women don't want to have sex with them for a long time. We've heard this.''

She questioned whether it was scientifically useful to identify the cad and dad types in literature.

''Looking at literature isn't going to let us advance evolutionary theory,'' Dr. Zuk said. ''You're just describing what you're seeing. You're not testing a hypothesis.''

Dr. Joseph Carroll, an English professor at the University of Missouri at St. Louis and a proponent of Darwinian literary analysis, argued that the study of Scott's heroes goes beyond confirming the cad-dad mating strategy. ''It illuminates it and illustrates it,'' he said. ''It gives you a more subtle and nuanced feel for the whole thing.''

Dr. E. Mavis Hetherington, emeritus professor of psychology at the University of North Carolina, who studies contemporary marriage and divorce, said the study affirmed what was already known.

''Are you surprised that women are attracted to cads?'' she asked. ''You wouldn't go out of your way to marry a cad, but if you had a little fling with him, it might be fun and exciting. He's probably a sensation-seeker, so you'd be going off to Mexico or going on ski trips or going to watch the bulls run at Pamplona.''

But affairs can be disruptive. ''Women are much more cautious than men about getting involved in them,'' Dr. Hetherington said. ''And when they do, it's much more likely to lead to the breakup of a marriage.''

Marine Worm Has Insectile and Vertebrate 'Eyes'

Marine Worm Has Insectile and Vertebrate 'Eyes'


By Bill Christensen

How did a complex structure like the human eye evolve? Charles Darwin recognized that the eye would be a real test of the theory of evolution. He suggested that it might be possible to evolve an eye from "imperfect and simple" forms:

"To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.

"Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real."

Scientists today believe that the eye could evolve from a single light-sensing cell. Scientists disagree over whether it evolved just once, or many times.

It turns out that Nature is both creative and generous with her gifts. Recent research has shown that the tiny marine worm Platynereis dumerilii has two types of light-sensing cells. The eyes of the worm have rhabdomeric photoreceptors, a compound lens formation that is seen almost exclusively in insect eyes. Rhabdomeric photoreceptors are covered in little finger-like protrusions. In its brain, however, it has a different kind of light-sensing cells - ciliary cells that are seen in vertebrate animals. Ciliary cells have hair-like cilia that extend outward and branch out like tiny umbrellas. Two different ways of sensing light in a single organism!

Researcher Joachim Wittbrodt of the European Molecular Biology Laboratory in Heidelberg, Germany speculates that the ciliary cells may regulate the worm's daily activity cycle, saying "We think they are related to circadian rhythms. We have found that there is a direct connection to the area used for locomotion... In the beginning we had a toolbox... what was in the brain in the worm ends up in our eye." If the animal had two copies of the genes needed to make one kind of photoreceptor, speculates Wittbrodt, then the extra set would have been free to evolve into the other photoreceptor. Different animals would subsequently evolve to use the two options in different ways.

Science fiction authors do not have the constraints of being able to use only Earth DNA; they are free to imagine light-sensing cells in wildly different ways. Here is a small sample of the variety found in sf:

His sense organs were gathered in clusters at the site of a man's ears; his visage... was corrugated muscle, not dissimilar to the look of the uncovered human brain. [The Meks from The Last Castle by Jack Vance]

Facing him from the middle of the room was something neither human nor humanoid. It stood on three legs, and it regarded Louis Wu from two directions, from two flat heads mounted on flexible, slender necks. Over most of its startling frame, the skin was white and glovesoft; but a thick, coarse brown mane ran from between the beasts necks, back along its spine, to cover the complex-looking hip joint of the hind leg. The two forelegs were set wide apart, so that the beast's small, clawed hooves formed almost an equilateral triangle.
Louis guessed that the thing was an alien animal. In those flat heads there would be no room for brains. But he noticed the hump that rose between the bases of the necks, where the mane became a thick protective mop... and a memory floated up from eighteen decades behind him.

This was a puppeteer, a Pierson's puppeteer. Its brain and skull were under the hump. It was not an animal; it was at least as intelligent as a man. And its eyes, one to a head in deep bone sockets, stared fixedly at Louis Wu from two directions. [The Puppeteers from Ringworld by Larry Niven]

"Its body architecture has been redesigned for greater efficiency, our useless simian hangovers have been left out, and its organs have been rearranged in a more sensible fashion...You can't say its not human, for it is .. an improved model. Take that extra appendage at the wrist. That's another hand, a miniature one... backed up by a microscopic eye. You can see how useful that would be, once you get used to the idea..." [The genetically-modified humans from Methuselah's Children by Robert Heinlein]

Sea Slug Offers Clues to Human Brain Disorders

Sea Slug Offers Clues to Human Brain Disorders

By Jeanna Bryner, LiveScience Staff Writer

Leonid Moroz with a marine snail at the University of Florida Whitney Laboratory for Marine Bioscience. Credit: Sarah Kiewel/UF HSC News

Beneath a slimy façade, the sea slug is somewhat of a brainiac.

At any given time within a single brain cell of this marine snail (Aplysia), more than 10,000 genes are hard at work, suggests a new study looking at aspects of the sea slug's genome.

By probing the brain of Aplysia, researchers identified more than 100 genes similar to those associated with all major human neurological diseases and more than 600 genes controlling brain development.

The findings suggest that acts of learning or the progression of brain disorders do not take place in isolation, and instead stem from interactions between large clusters of genes within many cells.

Any insights into how the brain runs and the genes that orchestrate the brain activity are welcomed by neuroscientists. Until now, for instance, scientists have been largely in the dark about how genes shape circuits in the brain to enhance learning and memory.

"This improves the genetic data that is available on Aplysia by several orders of magnitude," said study team member Eric Kandel of Columbia University in New York.

Brain web

The marine slug has a relatively simple nervous system, with about 10,000 large neurons that can be easily identified, compared with about 100 billion neurons in humans. Even so, the animal is capable of learning and its brain cells communicate in ways identical to human neuron-to-neuron messaging.

Like a meticulously-crafted spider web, most neurons sport thousands of strands that connect to other neurons. To journey between certain neurons, a signal must flow along the correct strands and intersections. Similarly, to store a memory that pathway, called a synapse, must be strengthened.

In past studies, scientists have found that once the route-map gets made, the sea slug marks the synapses connecting the relevant neurons. Next time the slug gets pinched, a certain protein gets sent out to all the synapses in a neuron. When the protein reaches a marked synapse, it triggers other molecules there to produce new proteins that strengthen the neuron-to-neuron connection.

Brainy conductor

To find out the genetic conductors of such learning and memory, scientists led by Leonid Moroz of the University of Florida Whitney Laboratory for Marine Bioscience studied gene activity in the sea slug's central nervous system, including genes known to switch on and off during a simple defensive maneuver--when the slug withdraws its gill.

Specifically they looked at the so-called transcriptome, a small percentage of genes that get copied to form molecules of ribonucleic acid (RNA). These molecules deliver directions for making proteins, which are key players in how cells operate.

They found specific genes linked to learning and memory. "We've now identified a whole bunch of receptors for serotonin. So we can see what their function is in various cells and which ones participate in the learning process," Kandel told LiveScience.

The scientists also analyzed 146 human genes implicated in 168 neurological disorders, including Parkinson's and Alzheimer's diseases, and genes controlling aging. They found 104 counterpart genes in Aplysia, suggesting the animal will be a valuable tool in understanding and ultimately treating neurodegenerative diseases.

The study is detailed in the Dec. 29 issue of the journal Cell.

Human Brain Has Origin in Lowly Worm

Human Brain Has Origin in Lowly Worm

By Robert Roy Britt, LiveScience Managing Editor


The origin of the human brain has been traced back to primitive central nervous systems in worms and bugs, researchers now say.

Humans and other vertebrates evolved from an ancient common ancestor that also gave rise to insects and worms, scientists have long known. But they're of course quite different today.

Vertebrates have a spinal cord running along their backs, but insects and annelid worms such as earthworms, which have simple organs that barely resemble a brain, have clusters of nerves organized in a chain along their bellies. So biologists have long assumed these systems—key to ultimately putting a brain to use—arose independently, only after the split.

In the new study, researchers at the European Molecular Biology Laboratory [EMBL] in Heidelberg examined they embryos of a marine annelid worm called Platynereis dumerilii, which has a nervous system unchanged for eons. They documented the molecular fingerprints of the developing nerve cells.

"Our findings were overwhelming," says study team member Alexandru Denes. "The molecular anatomy of the developing CNS [central nervous system ] turned out to be virtually the same in vertebrates and Platynereis. Corresponding regions give rise to neuron types with similar molecular fingerprints and these neurons also go on to form the same neural structures in annelid worm and vertebrates."

"Such a complex arrangement could not have been invented twice throughout evolution , it must be the same system," said Gáspár Jékely, another team member. "It looks like Platynereis and vertebrates have inherited the organization of their CNS from their remote common ancestors."

The results, published this month in the journal Cell, leave a nagging question: How did the central nervous systems get flipped from belly to backside or vice-versa?

"How the inversion occurred and how other invertebrates have modified the ancestral CNS throughout evolution are the next exciting questions for evolutionary biologists," said study leader Detlev Arendt.

Death of an order: a comprehensive molecular phylogenetic study confirms that termites are eusocial cockroaches

Biology Letters ISSN: 1744-9561 (Paper) 1744-957X (Online) Issue: Volume 3, Number 3 / 07 June 2007 Pages: 331–335 DOI: 10.1098/rsbl.2007.0102 Download PDF

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Phylogeny

Death of an order: a comprehensive molecular phylogenetic study confirms that termites are eusocial cockroaches

Daegan Inward^†, George Beccaloni & Paul Eggleton^*

Soil Biodiversity Group, Department of Entomology, The Natural History Museum, London SW7 5BD, UK

*Author for correspondence p.eggleton@nhm.ac.uk

Received 21 February 2007; Accepted 14 March 2007; Revised 14 March 2007; Published online 5 April 2007

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Abstract

Termites are instantly recognizable mound-builders and house-eaters: their complex social lifestyles have made them incredibly
successful throughout the tropics. Although known as 'white ants', they are not ants and their relationships
with other insects remain unclear. Our molecular phylogenetic analyses, the most comprehensive yet attempted, show that termites are social cockroaches, no longer meriting being classified as a separate order (Isoptera) from the cockroaches (Blattodea). Instead, we propose that they should be treated as a family (Termitidae) of cockroaches. It is surprising to find that a group of wood-feeding cockroaches has evolved full sociality,
as other ecologically dominant fully social insects (e.g. ants, social bees and social wasps) have evolved from solitary predatory
wasps.

Keywords: insect systematics; phylogenetics; social evolution; classification

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1. Introduction

Termites, cockroaches and mantids form a well-established lineage, the Dictyoptera, uniquely defined by having a perforation in the tentorium (the internal skeletal part of the head)
and enclosing their eggs within a specialized case (ootheca). Within the Dictyoptera, there is agreement that both termites and mantids are monophyletic groups. However, hypotheses of relationships among the three groups have provoked controversy ever
since the finding that the woodroach Cryptocercus shares several groups of symbiotic gut flagellates with early branching termites (Cleveland et al. 1934). This, together with morphological similarity between some termites' nymphs (pseudergates) and Cryptocercus nymphs, suggested a close phylogenetic relationship between the two groups (McKitterick 1964). However, some researchers have challenged this hypothesis by showing that (i) gut flagellates could have been passed from
termites to Cryptocercus early in the history of the groups (Thorne 1990) and (ii) in phylogenetic studies (Thorne & Carpenter 1992; Kambhampati 1995), albeit with sparse taxon sampling, termites did not group with Cryptocercus or indeed nest within cockroaches. However, these results have been contested and recent phylogenetic studies (Lo et al. 2003; Terry & Whiting 2005), again, unfortunately, with sparse taxon sampling, have supported the original hypothesis of a monophyletic termites+cockroaches.

Two questions must be answered to resolve the phylogenetic position of termites. Are termites cockroaches? And if they are, what is the sister group of the termites within the cockroaches? No previous study has answered these questions unambiguously, as none of them have sufficiently comprehensive taxon sampling
or completely adequate character information. Here, we provide definitive answers by sampling, for the first time, a fully
representative set of Dictyoptera species and sequencing and analysing five gene loci.

2. Material and methods

We sampled 107 Dictyoptera (in-group) species along with 11 out-groups. This included five of the 15 mantid families, all
six cockroach families as well as 22 of the 29 cockroach subfamilies and all termite families and subfamilies. We used five
gene loci (two mitochondrial: 12S, and cytochrome oxidase II; and three nuclear: 28S, 18S and histone 3), which gave us approximately 4900 aligned base pairs. We estimated substitution models for each gene (Posada & Crandall 1998) and subsequently employed a Bayesian analysis (Ronquist & Huelsenbeck 2003) on the combined dataset to estimate tree topology and posterior probabilities for each node and for nodes not recovered
in a majority of the trees. We also undertook a maximum parsimony (MP) analysis on the same aligned dataset. Full details
of the methods are in the electronic supplementary material.

3. Results and discussion

Our Bayesian consensus tree (figure 1) answers both the questions: termites nest within the cockroaches and Cryptocercus is the sister group of the termites. Additionally, it shows termite+Cryptocercus clade as sister to Blattidae, and that combined clade as sister to Blattellidae+Blaberidae ('Blaberoidea'
in figure 1). Polyphagidae+Nocticolidae ('Polyphagoidea') are then sister to all the other cockroaches (including
the termites) and the mantids are sister to the cockroaches. Most of these relationships have 100% posterior probabilities, meaning
that none of the 2501 sampled trees in the Bayesian analysis recover any other relationship. The probability of termites falling
outside the cockroaches, using our dataset, is therefore extremely small. Alternative topologies within the Dictyoptera were
statistically very unlikely (table 1). None of these alternative topologies affect our findings of a blattid+Cryptocercus+termite clade. The maximum parsimony analysis gives essentially the same tree topology as the Bayesian analysis,
with strong support for the key nodes (see electronic supplementary material, appendices).

			Figure 1 Topology of Bayesian majority rules consensus tree of 2501 trees. Red branch indicates position of Cryptocercus, blue branches indicate termite lineage. Numbers under the branches indicate posterior probabilities (i.e. the proportion of the 2501 sampled trees that contain the node) for key nodes. Names of major clades (e.g. superfamilies) are provisional.

			Table 1 Posterior probabilities (post p) and S-H tests (Diff -lnL) for alternative phylogenetic hypotheses when compared with our preferred tree. (Post p, posterior probabilities for nodes in Bayesian analysis. Probabilities for Shimodaira-Hasegawa (S-H) test: p<0.001, p<0.001-0.05, p<0.05-0.1. Key to abbreviations: Cyptoc, Cryptocercus; polyp, Polyphagoidea.)

How do these results compare with the earlier analyses of Dictyoptera? This is difficult to assess for many of the studies
because they have not included termites, or, what in retrospect is more misleading, have used termites as out-groups, therefore
specifically excluded them a priori from nesting within the cockroaches. However, considering only studies where all the Dictyoptera have been included unconstrained,
most recent studies support our findings (table 2), although not all these studies are independent: a number used some of the same genes as we have. The most comprehensive
of the studies in table 2 (Klass & Meier 2006), however, has the advantage that it uses a completely independent morphological dataset and, although it differs in some
basal parts of the tree (tables 1 and 2), it shows a strong level of support for a sister group relationship between termites and Cryptocercus and finds that this clade is nested within the cockroaches.

			Table 2 Summary of recent phylogenetic hypotheses concerning termites. (Endog, endoglucanase; H3, histone 3; , Taxon sampling too scanty to allow a clear hypothesis of position of termites within the Blattodea; T in B, termites nested within Blattodea?; T/C sister, termites and Cryptocercus sister groups? Papers discuss Blattodea relationships in isolation are not included here. No. of roaches, Number of cockroach (minus termites) families/subfamilies/genera/species in the various studies.)

Even given this growing consensus, however, most previous researchers appear to have had little problem with accepting that
termites could both be nested within the cockroaches and that termites (a clade) could still be considered as an order separate
from the cockroaches (a grade). At the same time, however, most systematists now generally believe that formal taxonomic groupings
should be monophyletic (Benton 2000). Therefore, we are led logically to the conclusion that the presently recognized order Blattodea is not an acceptable taxon
if it does not include the termites, as it does not contain an ancestor and all its descendants. The finding that the termites
are nested within the cockroaches causes a classificatory problem that we believe can best be resolved by changing the taxonomic
rank of the termites. We propose that the presently recognized order Isoptera should no longer be used and that the species
presently included in Isoptera should be classified within the family Termitidae as part of the order Blattodea within the
superorder Dictyoptera. This means that the existing termite taxa need to be downgraded by one taxonomic rank (i.e. families
become subfamilies, subfamilies become tribes; see electronic supplementary material), but would otherwise remain unchanged
in species composition.

This result may appear surprising to many people who are aware that termites have apparently very different life history and
social behaviours from cockroaches. However, it is scarcely unparalleled. Ants, social wasps and bees are also generally strikingly different in
many aspects of their biologies from their closest solitary relatives. The evolution of sociality clearly has the propensity
to change the nature of clades fundamentally, such that just four families of eusocial insects (Formicidae, Vespidae, Apidae
and Termitidae) have come to dominate vital ecosystem processes (predation, pollination and decomposition; Grimaldi & Engel 2005).

Our findings allow the pathway to eusociality in termites to be reconstructed with more certainty (figure 2) and they generally support recent hypotheses based on nutritional and microbiological arguments (Nalepa et al. 2001). Termites have evolved from omnivorous cockroach ancestors with a diploid reproductive system that form their oothecae internally
and exhibit different degrees of intraspecific coprophagy (faeces eating) and gregariousness. These last two characteristics
have allowed specifically co-evolved gut symbioses to evolve, as facilitative coprophagy by conspecifics allows the transmission of a stable microbial
assemblage from generation to generation. The key evolutionary shift appears to be the acquisition of mutualistic cellulolytic
flagellates in the ancestor of termites and Cryptocercus that allowed the cockroaches to become wood feeding (although this shift is not only found in the termite+Cryptocercus clade within cockroaches, Brugerolle et al. 2003). Offspring of these wood-feeding cockroaches required lengthy parental contact to allow flagellate transfer between generations
by proctodeal trophallaxis (nutrient transfer from the anus of one individual to the mouth of another; Nalepa et al. 2001). The subsequent shift to eusociality in the termites has involved reduction and eventual loss of the oothecae, as protection
from desiccation is unnecessary inside a nest with a controlled internal climate. There has also been a trend towards monogamy,
with progressive anatomical simplification of termite sperm (Baccetti et al. 1981) and reduction in complexity of the male genitalia (Klass et al. 2000), presumably due to lowered sperm competition. In addition, establishment of permanent family groups (colonies) has led to the evolution of sterile worker and soldier castes
in response to the need for foragers, alloparental care, nest builders and colony defenders (Higashi et al. 2000).

			Figure 2 Simplified phylogenetic tree showing major evolutionary transitions within ancestral forms leading to the termites. 1, ootheca formed from secretions of the asymmetrical accessory glands; 2, ootheca formed internally in vestibulum, keel pointing upwards until deposited; 3, wood -feeding, unique hypermastigid and oxymonad gut flagellate assemblages, biparental care, proctodeal trophallaxis; and 4, male genitalia bilaterally symmetrical and much reduced, sperm immotile or weakly motile, true soldier caste, overlapping generations with reproductive division of labour ('eusociality').

Our reconstruction emphasizes the strikingly different routes of Hymenoptera and Dictyoptera to eusociality. Ants, arguably
the closest biological analogues of termites, have evolved from multiply provisioning predatory wasps (Wilson & Holldobler 2005) with a haplo-diploid reproductive system, phylogenetic and life-history characteristics far removed from those found in
cockroaches. Any general theory explaining the evolution of insect eusociality must take these profound evolutionary differences
fully into account.

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Acknowledgements

We thank all colleagues who donated material (see electronic supplementary material, appendix 7) and Alfried Vögler
for advice on molecular phylogenetics. This research was funded by a UK Leverhulme grant to P.E. and by an NHM Entomology
DRF grant to P.E. and G.B.

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^†Present address: Forest Research, Alice Holt Lodge, Farnham, Surrey GU10 4LH, UK

Electronic supplementary material is available at http://dx.doi.org/10.1098/rsbl.2007.0102 or via http://www.journals.royalsoc.ac.uk.

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This journal is © 2007 The Royal Society

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Voting: In Your Genes?

BEHAVIOR GENETICS ASSOCIATION:
Voting: In Your Genes?

Constance Holden

BEHAVIOR GENETICS ASSOCIATION, 25-28 JUNE, LOUISVILLE, KENTUCKY

How strong do you lean? Twin studies suggest that the intensity of a person's partisan attachment, and even whether that person votes, may be influenced by genes. CREDIT: CARLOS BARRIA/REUTERS /LANDOV

Behavior geneticists say almost every human behavior that can be reliably measured--from TV-watching to optimism--is significantly influenced by genes. Now they're extending their reach into the voting booth.

Numerous studies over the past 2 decades, the first led by psychologist Nicholas Martin at the Queensland Institute for Medical Research in Australia, have indicated that genes have a significant influence over whether you're "liberal" or "conservative" on various political and social issues. Some heritability estimates have been as high as 50%. That's roughly the heritability found for many personality traits such as "extraversion" or "agreeableness," and it implies that, in a given population, about half of the variation in a particular trait is attributable to genetic differences.

Now James Fowler, a political scientist at the University of California, San Diego, and grad student Christopher Dawes say they've produced fresh evidence that DNA also has a hand in the intensity of someone's partisan attachment and even in whether someone bothers to vote.

As they reported here, they did that by crunching data from twin registries and the government's long-running National Longitudinal Study of Adolescent Health (NLSAH). In one study, the researchers matched data on voting by 396 Los Angeles-area twins, including identical (who share 100% of their genes) and fraternal (who average 50% genetic overlap) twins, obtained from Los Angeles voter-turnout records. All twins were same-sex pairs to avoid confounding results with sex differences. The researchers corrected for environmental factors such as whether more of the identical than fraternal twins were living together, which might inflate their degree of similarity. The researchers concluded that the correlation for voting was much higher between pairs of identical (.71) than fraternal (.50) twins. From this they estimated the heritability of voting behavior--that is, whether people eligible to vote actually do so--at 53%, suggesting that at least half the individual variation can be traced to genetic influences. They found an even higher heritability--72%--when they replicated the study with data on 806 twins from NLSAH, they reported in the May issue of the American Political Science Review.

The San Diego researchers also argued for a biological twist to how strongly someone identifies with a given party. The group, led by grad student Jaime Settle, gave questionnaires to 353 pairs of same-sex twins in Twinsburg, Ohio, where twins from all over the world hold a summer gathering every year. The twins were asked to rank their partisan attachment on a seven-point scale. From that, the researchers report in an as-yet-unpublished paper, they calculated a heritability of 46% for party loyalty, independent of affiliation. Whereas "partisan direction" seems mainly influenced by social and demographic factors, the researchers conclude, "partisan intensity" is not.

Several groups are now trying to correlate personality data with DNA markers from studies such as NLSAH, which contains DNA as well as behavioral data from many subjects, in hope of identifying specific genes that feed into underlying traits, such as "desire for cooperation," that Fowler, for one, believes have been selected for throughout human evolution. Studies so far have focused on the same genes that are of interest in psychiatric genetics--in particular those involved with neurotransmitters such as dopamine and serotonin that are known to be important in regulating higher brain activities.

The heritability studies are "intriguing," says David Goldman, chief of the neurogenetics lab at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland. But he is skeptical about attempts to translate findings from twin and family studies into molecular hypotheses. "In any questionnaire you'll find heritability," he says, "but you don't know what's being inherited." So "it's premature at best to attack a complex phenotype like political leanings at the molecular level."

Martin, who pioneered twin studies on such behaviors, applauds social scientists for plunging into biological and evolutionary issues. At least some "are starting to acknowledge that humans are genetically unique individuals and not just cloned pawns" of their environment. And that suggests that prophets and pundits, however prescient, are probably never going to get much better at predictions than they are now.

DIVERSITY: Gender Similarities Characterize Math Performance

DIVERSITY:
Gender Similarities Characterize Math Performance

Janet S. Hyde,^1* Sara M. Lindberg,¹ Marcia C. Linn,² Amy B. Ellis,³ Caroline C. Williams³

Gender differences in mathematics performance and ability remain a concern as scientists seek to address the underrepresentation of women at the highest levels of mathematics, the physical sciences, and engineering (1, 2). Stereotypes that girls and women lack mathematical ability persist and are widely held by parents and teachers (3-5).

Meta-analytic findings from 1990 (6, 7) indicated that gender differences in math performance in the general population were trivial, d = -0.05, where the effect size, d, is the mean for males minus the mean for females, divided by the pooled within-gender standard deviation. However, measurable differences existed for complex problem-solving beginning in the high school years (d = +0.29 favoring males), which might forecast the underrepresentation of women in science, technology, engineering, and mathematics (STEM) careers.

Since this study of data from the 1970s and 1980s, several crucial cultural shifts have occurred that merit a new analysis of gender and math performance. In previous decades, girls took fewer advanced math and science courses in high school than boys did, and girls' deficit in course taking was one of the major explanations for superior male performance on standardized tests in high school (8). By 2000, high school girls were taking calculus at the same rate as boys, although they still lagged behind boys in the number of them taking physics (9). Today, women earn 48% of the undergraduate degrees in mathematics, although gender gaps in physics and engineering remain large (10).

Grade	d ± SE	Variance ratio	N
Grade 2	0.06 ± 0.003	1.11	460,980
Grade 3	0.04 ± 0.002	1.11	754,894
Grade 4	-0.01 ± 0.002	1.11	763,155
Grade 5	-0.01 ± 0.002	1.14	929,155
Grade 6	-0.01 ± 0.002	1.14	886,354
Grade 7	-0.02 ± 0.002	1.16	898,125
Grade 8	-0.02 ± 0.002	1.21	837,979
Grade 9	-0.01 ± 0.003	1.14	608,229
Grade 10	0.04 ± 0.003	1.18	619,591
Grade 11	0.06 ± 0.003	1.17	446,381

Effect sizes across grades for U.S. mathematics
tests; results are similar across grades 2 through 11.

Percentage of children scoring above indicated percentile and ratios
Ethnic group	Above 95th percentile			Above 99th percentile
	F	M	M/F	F	M	M/F
Asian/Pacific Islander (n =219)	5.71	6.27	1.09	1.37	1.25	0.91
White (n = 3473)	5.38	7.80	1.45	0.90	1.85	2.06

The upper tail. Percentage of Minnesota children scoring above the 95th and
99th percentiles in 11th grade mathematics testing, by gender and ethnicity. Too
few students scored above the 95th percentile to compute reliable statistics for
these groups: American Indians, Hispanics, and Black not Hispanic.

Contemporary state assessments. State assessments of cognitive performance provide a contemporary source of data on these questions. Many states have conducted assessments for years, but with the advent of No Child Left Behind (NCLB) legislation, all states are mandated to conduct such assessments annually. This testing provides an exceptional opportunity to analyze current gender differences in math performance, particularly because of the extraordinary number of test takers.

Although NCLB requires states to post test results publicly, few states report data by gender and, of those that do, fewer report the necessary statistical information to compute effect sizes. Therefore, we contacted the state departments of education of all 50 states, requesting detailed statistical information on gender differences, by grade level and by ethnicity. Responses with adequate statistical information were received from 10 states: California, Connecticut, Indiana, Kentucky, Minnesota, Missouri, New Jersey, New Mexico, West Virginia, and Wyoming. In all cases, the data represent the testing of all students attending school in that grade. These states are geographically diverse and appear to be representative of all 50 states insofar as their average scores on the National Assessment of Educational Progress (NAEP, a federal assessment that carefully samples students nationwide) match the average for all 50 states quite closely. For 8th-graders, the average NAEP mathematics score was 280.22 for our 10 states and 280.17 for all 50 states (11).

Gender and average performance. Effect sizes for gender differences, representing the testing of over 7 million students in state assessments, are uniformly <0.10, representing trivial differences (see table, top left, and table S1). Of these effect sizes, 21 were positive, indicating better performance by males; 36 were negative, indicating better performance by females; and 9 were exactly 0. From this distribution of effect sizes, we calculate that the weighted mean is 0.0065, consistent with no gender difference (see chart on p. 495 and fig. S1). In contrast to earlier findings, these very current data provide no evidence of a gender difference favoring males emerging in the high school years; effect sizes for gender differences are uniformly <0.10 for grades 10 and 11 (see table, top left, and table S1). Effect sizes for the magnitude of gender differences are similarly small across all ethnic groups (table S2). The magnitude of the gender difference does not exceed d = 0.04 for any ethnic group in any state.

Gender and variance.Another explanation for the underrepresentation of women at the highest levels in STEM careers has focused not on averages, but on variance, the extent to which scores of one gender or the other vary from the mean score. The hypothesis that the variability of intellectual abilities is greater among males than among females and produces a preponderance of males at the highest levels of performance was originally proposed over 100 years ago (12).

The variance ratio (VR), the ratio of the male variance to the female variance, assesses these differences. Greater male variance is indicated by VR > 1.0.All VRs, by state and grade, are >1.0 [range 1.11 to 1.21 (see top table on p. 494)]. Thus, our analyses show greater male variability, although the discrepancy in variances is not large. Analyses by ethnicity show a similar pattern (table S2).

Effect sizes across grades and U.S. states. The weighted mean is 0.0065, consistent with no gender difference. Each square represents the effect size for one grade within one state. New Mexico (pea green), Kentucky (pink), Wyoming (dark brown), Minnesota (teal), Missouri (red), West Virginia (gold), Connecticut (tan), California (orange), Indiana (yellow), New Jersey (purple).

Does this greater variability translate into gender differences at the upper tail of the distribution (13)? Data from the state assessments provide information on the percentage of boys and girls scoring above a selective cut point. Results vary by ethnic group. The bottom table on p. 494 shows data for grade 11 for the state of Minnesota. For whites, the ratios of boys:girls scoring above the 95th percentile and 99th percentile are 1.45 and 2.06, respectively, and are similar to predictions from theoretical models. For Asian Americans, ratios are 1.09 and 0.91, respectively. Even at the 99th percentile, the gender ratio favoring males is small for whites and is reversed for Asian Americans. If a particular specialty required mathematical skills at the 99th percentile, and the gender ratio is 2.0, we would expect 67% men in the occupation and 33% women. Yet today, for example, Ph.D. programs in engineering average only about 15% women (14).

Gender and item complexity. An additional issue in assessing gender differences in math performance and the underrepresentation of women in STEM careers is the question of the cognitive complexity or depth of knowledge being tested. Earlier studies (6) indicated that, although girls equaled or surpassed boys in basic computation and understanding of mathematical concepts, boys exceeded girls in complex problem-solving beginning in the high school years, d = + 0.29. Complex problem-solving is crucial for advanced work in STEM careers. At the time of the 1990 meta-analysis, girls were less likely to take advanced math and science courses, and this gender difference in course choice was a likely explanation for the gender gap in complex problem-solving (8).

Today, with the gender gap erased in taking advanced math courses, does the gender gap remain in complex problem-solving? To answer this question, we coded test items from all states where tests were available, using a four-level depth of knowledge framework (15). Level 1 (recall) includes recall of facts and performing simple algorithms. Level 2 (skill/concept) items require students to make decisions about how to approach a problem and typically ask students to estimate or compare information. Level 3 (strategic thinking) includes complex cognitive demands that require students to reason, plan, and use evidence. Level 4 (extended thinking) items require complex reasoning over an extended period of time and require students to connect ideas within or across content areas as they develop one among alternate approaches. We computed the percentage of items at levels 3 or 4 for each state for each grade, as an index of the extent to which the test tapped complex problem-solving. The results were disappointing. For most states and most grade levels, none of the items were at levels 3 or 4. Therefore, it was impossible to determine whether there was a gender difference in performance at levels 3 and 4.

The dearth of level-3 or level-4 items in state assessments has an additional serious consequence. With the increased emphasis on testing associated with NCLB, more teachers are gearing their instruction to the test (16). If the tests do not assess the sorts of reasoning that are crucial to careers in STEM disciplines, then these skills may be neglected in instruction, putting American students at a disadvantage relative to those in other countries where tests and curricula emphasize more challenging content (17).

To address this limitation in the state assessments, we returned to the NAEP data (18). NAEP categorizes items as easy, medium, or hard. We coded hard sample items for depth of knowledge. No items were at level 4 but many were at level 3. We computed the magnitude of gender differences on the hard items that were at level 3 depth of knowledge. At grade 12, effect sizes for these items ranged between 0 and 0.15 (average d = 0.07). At grade 8, effect sizes for these items ranged between 0 and 0.08 (average d = 0.05). Thus, even for difficult items requiring substantial depth of knowledge, gender differences were still quite small.

Conclusion. Our analysis shows that, for grades 2 to 11, the general population no longer shows a gender difference in math skills, consistent with the gender similarities hypothesis (19). There is evidence of slightly greater male variability in scores, although the causes remain unexplained. Gender differences in math performance, even among high scorers, are insufficient to explain lopsided gender patterns in participation in some STEM fields. An unexpected finding was that state assessments designed to meet NCLB requirements fail to test complex problem-solving of the kind needed for success in STEM careers, a lacuna that should be fixed.

References and Notes

1. National Academy of Sciences, Beyond Bias and Barriers: Fulfilling the Potential of Women in Academic Science and Engineering (National Academies Press, Washington, DC, 2006).
   
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7. General guidelines are that d = 0.20 is a small effect, d = 0.50 is moderate, and d = 0.80 is large (20).
   
8. J. L. Meece et al., Psychol. Bull. 91, 324 (1982).
   
   
9. NSF, Science and Engineering Indicators 2006, www.nsf.gov/statistics/seind06/ (2006).
   
10. NSF, www.nsf.gov/statistics/wmpd/underdeg.htm (2004).
    
11. National Assessment of Educational Progress, http://nces.ed.gov/nationsreportcard/nde/statecomp/ (2008).
    
12. S. A. Shields, Am. Psychol. 30, 739 (1975).
    
13. L. V. Hedges, L. Friedman, Rev. Educ. Res. 63, 94 (1993).
    
    
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15. N. L. Webb, Appl. Meas. Educ. 20, 7 (2007).
    
16. W. Au, Educ. Res. 36 258 (2007).
    
    
17. K. Roth, H. Garnier, Educ. Leadership 64, 16 (2006).
    
18. National Assessment of Educational Progress, http://nces.ed.gov/nationsreportcard/itmrls/startsearch.asp (2008).
    
19. J. S. Hyde, Am. Psychol. 60, 581 (2005).
    
20. J. Cohen, Statistical Power Analysis for the Behavioral Sciences (Lawrence Erlbaum, Hillsdale, NJ, 1988).
    
    
21. We thank personnel in each of the 10 responding states for providing data. Special thanks to Margaret Biggerstaff of the Minnesota Department of Education for additional analyses. This research was funded through grant REC 0635444 from NSF. Any findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Supporting Online Material

www.sciencemag.org/cgi/content/full/321/5888/494/DC1

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10.1126/science.1160364

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¹Department of Psychology, University of Wisconsin, 1202 West Johnson Street, Madison, WI 53706, USA

²Education in Mathematics, Science, and Technology, University of California, Berkeley, Berkeley, CA 94720, USA

³Department of Curriculum and Instruction, University of Wisconsin, Madison, WI 53706, USA

^*Author for correspondence. E-mail: jshyde{at}wisc.edu