Below I note that sex matters when it comes to evolution, specifically in the case of how sexual reproduction forces the bits of the genome to be passed back and forth across sexes. In fact, the origin of sex is arguably the most important evolutionary question after the origin of species, and it remains one of the most active areas of research in evolutionary genetics. More specifically the existence of males, who do not bear offspring themselves but seem to be transient gene carriers is a major conundrum. But that’s not the main issue in this post. Let’s take the existence of males as a given. How do sex differences play out in evolutionary terms shaping other phenotypes? Consider Bateman’s principle:

Bateman’s principle is the theory that females almost always invest more energy into producing offspring than males, and therefore in most species females are a limiting resource over which the other sex will compete.

Female ova are energetically more expensive, and scarcer, than male sperm. Additionally, in mammals and other live-bearing species the female invests more time and energy after the point of fertilization but before the young exhibit any modicum of organismic independence (the seahorse being the exception). And, often the female is the “primary caregiver” in the case of species where the offspring require more care after birth. The logic of Bateman’s principle is so obvious when its premises are stated that it easily leads to a proliferation of numerous inferences, and many data are “explained” by its operation (in the biological anthroplogist Sarah Hrdy moots the complaint that the principle is applied rather too generously in the context of an important operationally monogamous primate, humans).

But the general behavioral point is rooted in realities of anatomy and life-history; in many dioecious species males and females exhibit a great deal of biological and behavioral dimorphism. But the direction and nature of dimorphism varies. Male gorillas and elephant seals are far larger than females of their kind, but among raptors females are larger. If evolution operated like Newtonian mechanics I assume we wouldn’t be theorizing about why species or sex existed at all, we’d all long ago have evolved toward perfectly adapted spherical cows floating in our own effluvium, a species which is a biosphere.

Going beyond what is skin deep, in humans it is often stated that males are less immunologically robust than females. Some argue that this is due to higher testosterone levels, which produce a weakened immune system. Amtoz Zahavi might argue that this is an illustration of the ‘handicap principle’. Only very robust males who are genetically superior can ‘afford’ the weakened immune system which high testosterone produces, in addition to the various secondary sexual characteristics beloved of film goers. Others would naturally suggest that male behavior is to blame. For example, perhaps males forage or wander about more, all the better to catch bugs, and they pay less attention to cleanliness.

But could there be a deeper evolutionary dynamic rooted in the differential behaviors implied from Bateman’s principle? A new paper in The Proceedings of the Royal Society explores this question with a mathematical model, The evolution of sex-specific immune defences:
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Fascinating post by Bayes, Phylogenetics, cultural evolution and horizontal transmission:

For some time now, evolutionary biologists have used phylogenetics. It is a well-established, powerful set of tools that allow us to test evolutionary hypotheses. More recently, however, these methods are being imported to analyse linguistic and cultural phenomena. For instance, the use of phylogenetics has led to observations that languages evolve in punctuational bursts, explored the role of population movements, and investigated the descent of Acheulean handaxes. I’ve followed the developments in linguistics with particular interest; after all, tracing the ephemeral nature of language is a daunting task. The first obvious road block is that prior to the invention of writing, the uptake of which is limited in geography and history, language leaves no archaeological record for linguists to examine. One particular note I’d like to make is that when Charles Darwin first formulated his theory of natural selection, he took inspiration from linguistic family trees as the basis for his sketch on the evolutionary tree of life. So it seems rather appropriate that phylogenetic approaches are now being used to inform our knowledge regarding linguistic evolution.

Like many other attempts applying evolutionary thinking in culture, phylogenetic approaches are, at times, met with contempt. This stems from assertions that cultural evolution and biological evolution differ greatly in regards to the relative importance of horizontal transmission….

…

I guess the general points to take away from this post are: 1) Do not necessarily assume horizontal transmission is dominant in shaping culture; and, 2) Even with certain levels of reticulation, it does not necessarily invalidate a phylogenetic approach in investigating cultural and linguistic evolution.

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Earlier I pointed to the possibility of biophysical constraints and parameters in terms of inheritance shaping the local trajectory of evolution. Today Olivia Judson has a nice post [link fixed] on how the existence of two sexes in many species results in a strange metastable tug-of-war in terms of phenotypic evolution:

In sum, the traits that make a “good” male are often different from those that make a “good” female. (Note: I’m only talking about “good” in evolutionary terms. That means a trait that improves your chance of having surviving offspring.) Since many of these traits have a genetic underpinning, male and female genes are thus being sculpted by different forces.

But — and this is the source of the tension I mentioned — males and females are formed from the same underlying set of genes. After all, in humans, whether you’re a boy or a girl comes down to whether you have a Y chromosome or not: boys do, girls don’t. The rest of the genes occur in both sexes.

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For some time now, evolutionary biologists have used phylogenetics. It is a well-established, powerful set of tools that allow us to test evolutionary hypotheses. More recently, however, these methods are being imported to analyse linguistic and cultural phenomena. For instance, the use of phylogenetics has led to observations that languages evolve in punctuational bursts, explored the role of  population movements, and investigated the descent of Acheulean handaxes. I’ve followed the developments in linguistics with particular interest; after all, tracing the ephemeral nature of language is a daunting task. The first obvious road block is that prior to the invention of writing, the uptake of which is limited in geography and history, language leaves no archaeological record for linguists to examine. One particular note I’d like to make is that when Charles Darwin first formulated his theory of natural selection, he took inspiration from linguistic family trees as the basis for his sketch on the evolutionary tree of life. So it seems rather appropriate that phylogenetic approaches are now being used to inform our knowledge regarding linguistic evolution.

Like many other attempts applying evolutionary thinking in culture, phylogenetic approaches are, at times, met with contempt. This stems from assertions that cultural evolution and biological evolution differ greatly in regards to the relative importance of horizontal transmission, as evinced in these two quotes:

The course of organic evolution can be portrayed properly as a tree of life, as Darwin has called it, with trunk, limbs, branches, and twigs. The course of development of human culture in history cannot be so described, even metaphorically. There is a constant branching-out, but the branches also grow together again, wholly or partially, all the time. A branch on the tree of life may approach another branch; it will not normally coalesce with it. The tree of culture, on the contrary, is a ramification of such coalescences, assimilations, or acculturations – Alfred Kroeber (1948, pg. 138).

Human cultural evolution proceeds along paths outstandingly different from the ways of genetic change. Trees are correct topologies of biological evolution. In human cultural evolution, on the other hand, transmission and anastomosis are rampant. Five minutes with a wheel, a snowshoe, a bobbin, or a bow and arrow may allow an artisan of one culture to capture a major achievement of another – Stephen Jay Gould (1987, pg. 70).

Both Gould and Kroeber provide an interesting entry point into some of the criticisms of phylogenetics. Cladistic (phylogenetic) theories approach the problem of modelling culture from a historical perspective: languages, cultures and populations are primarily derived from a parent group. A visual representation of this would be a bifurcating tree. However, what the above quotes emphasise is a rhizotic (reticulate) approach, in which the focus is more geared towards a non-treelike representation of transmission: here, linguistic and cultural features are shaped by several different, antecedent groups. In considering these different mechanisms of transmission we are faced with two broad themes. The first thought is in regards to the relative influence of horizontal and vertical forms of transmission. Is there an overarching form of transmission that dominates the variation found in cultural and linguistic features? Or do we need to examine this on a case by case basis? So, for instance: some cases are dominated by vertical transmission, whilst other cases are dominated by horizontal transmission. Secondly, even if there is a reasonable level of horizontal influence, then does this invalidate the use of cultural phylogenies?

Addressing these issues are two papers. The first provides an overview of the relative importance of both horizontal and vertical intergroup transmission in human culture, and then applies these findings to chimpanzee cultural diversity. In the second, the authors test the robustness of phylogenetic inferences in regards to horizontal transmission.

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I stumbled onto this New York Times Magazine The Brothers Emanuel, from 1997. Zeke, Rahm and Ari Emanuel have all become even more accomplished over the past 13 years. But I was surprised to discover that they had a younger sister, and that her life prompted the brothers to reflect on the influence of genetics and environment on life outcomes. Here’s the relevant portion:

Today, the brothers argue just as passionately about the role that environment and genetics played in the life of their sister, who in recent years has been on and off the welfare rolls that Rahm worked so hard to cut. Benjamin Emanuel met his daughter when he gave her a well-baby checkup and discovered that she had suffered a brain hemorrhage at delivery. The baby’s future was unclear; Shoshana’s birth mother, a young woman of Polish Catholic background, asked Dr. Emanuel if he knew someone who wanted her child. ”But I couldn’t find placement,” Benjamin Emanuel says. After a week of debate between both parents and sons – Marsha Emanuel had always wanted a girl – the Emanuels themselves took Shoshana in. ”What are you going to do?” Benjamin Emanuel says philosophically.

Intellectually, Shoshana developed normally – like her brothers, she graduated from New Trier, one of the most competitive high schools in the country – but she needed four operations and years of physical therapy to give her 85 percent use of her left side. She had a difficult adolescence, and today Marsha Emanuel, at the age of 63, is raising Shoshana’s two illegitimate children. (None of the Emanuels will talk about Shoshana in detail, and she declined to be interviewed for this article.)

The conversation the brothers continue to have about Shoshana is also, of course, a conversation about themselves. Were Zeke, Rahm and Ari simply successful products of Jewish middle-class parents who valued education and hammered them with expectations? How much of their drive came from their immigrant father? Certainly each Emanuel brother derives a large part of his identity that of the others. No one else, it seemed, mattered as much. ”The pressure is that you were judged by the family,” Ari says. ”Our family never cared about the kid down the block.”

Ari Emanuel also seems to have some opinions about I.Q.:
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I notice that not too many people seem to have switched from the old feed to the new. Part of the issue is that many people have subscriptions which they never check or have forgotten. But in case you’re reading this on the old feed, that’s because the techs are currently pointing the old feed to the new. But at some point this will not occur, and you’ll need the new feed. So if you haven’t, please switch to:

Danke.

(thanks to Edmund for reminding me)

Ed reviews a new paper on the fall of the Angkor civilization. He concludes:

Of course, a changing environment was far from the only reason behind the fall of Angkor. By the time the droughts kicked in, the city was already weakened by social, economic and political strife. Buckley simply thinks that the climate simply sealed the city’s demise. In fact, others have suggested that some force may have pushed the local people to move from inland agriculture to maritime trade. Buckley says that this transition coincides neatly with the aftermath of the first drought.

An economic historian might term the droughts which Angkor was subjected to an “exogenous shock.” Basically an outside factor which slams into an equilibrium system periodically (I assume that super-droughts would exhibit a poisson distribution but readers more climatically savvy can correct me). On the other hand, there are parameters which are endogenous to the system; consider the institutional frameworks which regulate social relations and distribute economic surplus.
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If you have a blog, and you link to http://scienceblogs.com/gnxp/, I would appreciate it if you switched to http://blogs.discovermagazine.com/gnxp/. I know most people don’t use blogrolls much, but it matters for PageRank, and the archives have been copied so I’d rather have search engine traffic go to the active weblog ASAP. Thanks.

John Hawks has an excellent post rebutting some misinformation and confusion on the part of Colin Blakemore, an Oxford neurobiologist. Blakemore asserts that:

* There was a sharp spike in cranial capacity ~200,000 years ago, on the order of 30%

* And, that the large brain was not deleterious despite its large caloric footprint (25% of our calories service the brain) because the “environment of early humans was so clement and rich in resources”

Hawks refutes the first by simply reposting the chart the above (x axis = years before present, y axis = cranial capacity). It’s rather straightforward, I don’t know the paleoanthropology with any great depth, but the gradual rise in hominin cranial capacity has always been a “mystery” waiting to be solved (see and ). Blakemore may have new data, but as they say, “bring it.” Until then the consensus is what it is (the hominins with the greatest cranial capacities for what it’s worth were Neandertals, and even anatomically modern humans have tended toward smaller cranial capacities since the end of the last Ice Age along with a general trend toward smaller size).

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Matt Yglesias muses on the possible influence of Isaac Asimove’s Foundation series on the way he looks at the world. Interestingly, Paul Krugman admits his debt to this series as well in getting him interested in economics. Unlike Robert Heinlein or mentor John W. Campbell Asimov was a political liberal. It is not uncommon for nerdy males, who are disproportionately represented in the pundit-class, to go through a science fiction phase in their youth. It would be interesting to see how interests in various authors tracked their current political positioning (I’d bet money that Poul Anderson is more popular with people who work at the Cato Institute).

Note: William Sims Bainbridge’s explores the various demographic trends which characterize the science fiction subculture. Politically there’s a bimodal distribution between liberals and libertarians, with more traditional conservatives such as Jerry Pournelle being the exception.