Yesterday, while on a very long flight, I read the latest Seed Salon in Seed Magazine. It is a conversation between network theory guru Albert-Laszlo Barabasi (author of the bestseller “Linked”) and social scientist James Fowler (of the “Colbert Bump” fame). The two discuss the growing popularity of network representations of natural and human structures, including the internet, Facebook, and gene interaction networks. It is a very lively conversation, and quite good, with a few glaring exceptions. I’m going to highlight these.
About two-thirds of the way through the conversation, Barabasi points out that online social networks seem to differ fundamentally from “real-world” networks, in that online networks tend to have hub individuals. That is, they have popular individuals with many links, to whom are linked individuals with relatively fewer numbers of links. Similar patterns occur in many natural networks, such as metabolic and gene networks (though there are exceptions, and the jury is still out on many of these cases). But in real-world social networks, those hub or popular people tend to be linked to other popular people, not people with fewer links. Fowler then takes off with this, stating that recently, he and colleagues have found evidence that there’s a genetic basis for human social networks; the number of friends you possess is heritable. That is, if he is using the correct definition of heritability, the variance of the number of friends that individuals in a population possess, is largely explained by genetic variation among those individuals. Really?! Fowler goes on to list traits underlying “number of friends”, such as physical attractiveness, good communication skills, having assets, you know, all those things that we “know” to have a genetic basis in humans, and a genetic basis that we understand. Nevermind that earlier Barabasi pointed out the combinatoric basis of cancer in gene networks, in which more than 300 genes can be involved. Yet, Folwer implies that we can break down the possession of assets to genetic and Darwinian bases. I don’t disagree with Fowler when he says that Darwinian natural selection may play a role in the development of social networks, but that is a far cry from being able to list heritable traits, as well as understanding the strength of selection necessary for accomplishing this feat.
Gets worse, in my opinion. Barabasi is intrigued by Fowler’s idea,and goes on to give a somewhat counter-example. It has been noted that many biological (gene) networks are scale-free, and Barabasi points out that they are so, because of the constrained manner in which these networks grow. New genes tend to be added to a genome via duplication, and apparently in Barabasi’s hypothesis, only scale-free networks can emerge from this growth process. Fowler: “…if they’re all scale free, then that suggests that natural selection isn’t the cause.” Barabasi: “Right. … the scale-free state of the cell, the existence of hubs, is not because the cell has optimized itself to be resilient… It’s really coming from the way the cell… is created from the growth process.. Since hubs happen to be a desirable property, there is no reason for natural selection to delete them.” WHAT?!!! If anything, this is strongly suggestive of a role for selection in the evolution of the growth process itself. And, natural selection does not delete properties. If there is variation in a property, in this case the growth process or link distribution underlying a gene network, and that variation leads to a difference in performance, in this case resilience against gene disruption or deletion, then the variant that is borne by more offspring in the succeeding generation has been selected for. As simple as that. Otherwise, what would have constrained an ancient and ancestral molecular lineage from possessing a genome that grew as a random, Poisson network? It is absolutely premature to discount the role of selection here.
Okay, with my rant being over, Barabasi raises a very interesting question toward the end regarding a shift in the emphasis of scientific adventure to “humanity turning inward.” Fowler’s response is very insightful. If you’re interested, read the article; an online version is available here.