Most of you have probably already seen/heard about this, but check out true porn clerk stories.

A Mind for Sociability:

The amygdala, a small, almond-shaped area deep within our brains, appears to be essential in helping us read the emotions of others. Research shows that the structure is crucial for detecting fear, but scientists have also found evidence that it can help spot a wide variety of mental states…scientists noted that the amygdalas of patients with autism, which is characterized by decreased social interaction and an inability to understanding the feelings of others, have fewer nerve cells, especially in a subdivision called the lateral nucleus.
…
In humans, however, the lateral nucleus occupied a bigger fraction of the amygdala, and was larger compared to overall brain size, than in the other species, the team reports online today in the American Journal of Physical Anthropology. Although the functions of the amygdala’s subunits are unclear, the lateral nucleus makes more direct connections with the brain’s temporal lobe–which is involved in social behavior and the processing of emotions–than other parts of the amygdala make, the researchers note.

In Grooming, Gossip, and the Evolution of Language Robin Dunbar argued for the critical selective pressure of social groups in driving up the size and complexity of the human brain (and obviously, the emergence of language). This might explain the gradual increase in brain size over the past few million years until about 200,000 years B.P., but what about the Great Leap Forward & expansion out of Africa ~50,000 years ago? Remember, behaviorally modern humans postdated anatomically modern humans (e.g., a form of H. sapien which was gracile, high cranial vault, etc., was extant in Africa before expanding to the rest of the world) by 150,000 years. In The Dawn of Human Culture Richard Klein suggests that there was a biological change, a reorganization of the brain (Dunbar offers this idea as well). Greg has suggested that Neandertal introgression & hybrid vigor might have been at work; remember that Neandertals had the largest cranial volume of any Homo species. In The Prehistory of the Mind: The Cognitive Origins of Art, Religion and Science Steven Mithen suggests that the breakdown of separation between domain specific intelligennces (e.g., social intelligence, theory of mind, intuitive physics, folkbiology, etc.) was the critical factor in triggering the cultural revolution which lead to modernity. Mithen argues that the use of analogy to map across the various domains, and apply insights from each domain to the others, might have resulted in a massive increase in cognitive flexibility and creativity. A neurobiological implication that our species’ amygdala is more “hooked in” with our “higher cognitive functions” seems to lend some credence to that viewpoint.

Update: Kambiz has more.

Rapid evolution in early trilobites fueled by high variation:

Webster compiled morphological data for nearly 1,000 of the 17,000 different species of trilobites, a class of marine arthropods that died out by 250 million years ago, from 49 previously published sources. By tracking different morphological features — the number of body segments, for example — Webster found that trilobite species exhibited more variation during the Cambrian than in later periods, he reported in Science July 27. “Once you go beyond the Cambrian, the diversity of forms within any one species drops off,” he says.
Early and Middle Cambrian trilobite species, especially, exhibited greater morphological variations than their descendants. This high within-species variation provided more raw material upon which natural selection could operate, Webster says, potentially accounting for the high rates of evolution in Cambrian trilobites. Such findings may have implications for our understanding of the nature of evolutionary processes, he says.

I don’t know about the nature of the debate within paleontology (paleobiology) with great detail, but it seems that men like S.J. Gould and Niles Eldredge promoted “higher level” evolutionary processes to explain speciation and deep time natural history. This researcher seems to be putting the onus on basal microevolutionary processes.

How bacteria evolve into superbugs:

“Bacteria that can mutate fast will quickly adapt to harsh environments containing antibiotics. Our study showed that a high rate of immigration significantly augments the regular process of genetic mutation commonly used to explain the evolution of antibiotic resistance,” said co-author Dr. Andrew Gonzalez, a Canada Research Chair in Biodiversity and associate professor in the Department of Biology at McGill. Gonzalez explained that the flow of bacteria in the experiment is analogous to the immigration of bacteria-carrying individuals into a hospital, and “the rate at which bacteria are entering a particular environment – not just the fact that they are coming in – is a key factor.”

What species migrates a fair amount? Ultimately, recall that the rate of evolution is proportional extant genetic variation. That variation can be assumed to be “standing genetic variation” (the range already out there which is now subject to direction selection). Or, open can imagine the fountain of mutation always gushing, mostly with deleterious alleles which are purged, but on some occasions producing neutral alleles which remain extant at low frequencies, or positive alleles which increase in frequency (though stochastic dynamics are always operative). But then there is migration, which pools mutants from across multiple demes with permeable barriers. Selection doesn’t see provenance, whether it is a de novo mutation from within the population, or a de novo allelic brought via gene flow. Obviously one assumes that there will be a bias for alleles which drive evolution that arrived via gene flow to be positive and of large fitness effect. In any case, one doesn’t need to read a paper which explicitly fleshes out a population genetic demographic model (e.g., stepping stone, island, etc.): one can intuitively note that human societies have slowly become tied together by migration over the centuries, with some societies being the subject of mass population movements on a regular basis. One can connect the dots on the implications pretty easily….

When you’ve blogged for a while, and with some frequency, you wonder what this is all about. I don’t generally get too caught up in that, there’s more interesting stuff to contemplate. But, check out this from Google Analytics for the past 30 days of traffic for this website:

I’ve long known that most GNXP “readers” are “one off” events. I have no problem with that, if they find what they’re looking for then you’ve done some good. That being said, I was a little shocked (and pleased, frankly) to see that over 8,000 visitors have arrived over 200 times in the past 30 days! I don’t know, or care, about the details of how Google calculates this, rather, I’m interested in the gestalt sense of what’s going on. Obviously the same people don’t come everyday, but our unique visitor traffic has been in the 2,000-4,000 range for years, so these data together suggest that many people skip days (perhaps refreshing the site a lot on the weekend, or during one particular post where they participated in the thread?).

(click image for larger view)

Since we’re talking about sex & evolution I thought I would pass on this PNAS paper, Coevolution of robustness, epistasis, and recombination favors asexual reproduction (my emphasis). I covered statistical epistasis a few years ago, and at that point I was being told that synergistic epistasis was the critical cog that kept the species a rollin’ and a rockin’. But perhaps not (the paper is Open Access).

Looks like there might be a recantation of the argument against death for apostasy by the Grand Mufti of Egypt. Abu Aardvark has the details.

Viral Epizootic reveals inbreeding depression in a habitually inbreeding mammal:

Inbreeding is typically detrimental to fitness. However, some animal populations are reported to inbreed without incurring inbreeding depression, ostensibly due to past “purging” of deleterious alleles. Challenging this is the position that purging can, at best, only adapt a population to a particular environment; novel selective regimes will always uncover additional inbreeding load. We consider this in a prominent test case: the eusocial naked mole-rat (Heterocephalus glaber), one of the most inbred of all free-living mammals. We investigated factors affecting mortality in a population of naked mole-rats struck by a spontaneous, lethal coronavirus outbreak. In a multivariate model, inbreeding coefficient strongly predicted mortality, with closely inbred mole-rats (F ≥ 0.25) over 300% more likely to die than their outbred counterparts. We demonstrate that, contrary to common assertions, strong inbreeding depression is evident in this species. Our results suggest that loss of genetic diversity through inbreeding may render populations vulnerable to local extinction from emerging infectious diseases even when other inbreeding depression symptoms are absent.

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The Economist has a story about a mutant asexual crayfish lineage. It points out how this is a good test of the sex-is-good-against-disease thesis. The basic logic is that an allele which causes asexuality has a greater short term natural increase (because it has a 100% as opposed to 50% chance of being passed to the next generation). Nevertheless, because the conventional reshuffling that occurs during sexual reproduction through the synthesis of two haploid gametes into a diploid (as well as recombination) is not operative in a the clonal lineage, they are vulnerable to fast adapting pathogens which might wipe them out. One could conceptualize the modal genetic profile of the lineage as the selective pressure exerted upon the pathogens. In the case of an asexual lineage the the pathogen has a straight shot at a stationary adaptive peak (mutation of course will introduce variation over time). In contrast, sexual lineages with their wide distribution of of genetic architectures are like moving targets, as a population of pathogens shifts toward one peak, selection within the host population reshapes the adaptive landscape (remember the power of selection is proportional to extant heritable variation, which sexual lineages have in abundance vis-a-vis clonal ones). Imagine, if you will, a rugged adaptive landscape with many peaks always bubbling and morphing, as the pathogens race up the slopes the ground underneath them shifts and gives away and soon they find themselves having to traverse a radically altered surface. In contrast, an asexual population would exhibit one sharp peak of relative stability, and its lack of genetic variation means that the surface itself is relatively rigid and stable.

Note: Some researchers have proposed that the persistence of sex in complex organisms is a function of phylogenetic constraint. That is, once the lineages flipped from asexual to sexual they couldn’t flip back, even if it was adaptive. This sort of view is rather diminishes the power of selection to overcome phylogenetic hurdles. To my mind crayfish are a rather complex organism. But to those of you who know organismic biology: what is the most complex animal which can reproduce asexually? (I’m assuming it is a reptile?) It is supposed that imprinting prevents the emergence of asexuality in mammals.

People have bugged me about the “open thread” for a while, so by popular demand, it’s back. It will be to the right indefinitely, though I’ll purge it of old/tardish comments regularly. Please place interesting links/sites, etc. (this includes items of interest to young straight males, *hint*, *hint*).