CHAPTER 1 Introduction
CHAPTER 2 Nonlinear epigenetic variance: Review and simulations
CHAPTER 3 The nature of nurture: On the high heritability of cultural dependent cognitive abiliies
CHAPTER 4 A genetic origin of Black-White mean IQ differences? Weak inferences based on ambiguous results
CHAPTER 5 On the interpretation of the CHC factor Gc
CHAPTER 6 The relations among g loading, heritability, and cultural load: Do current theories of intelligence account for them?
CHAPTER 7 Discussion
Kan endorses a dynamic model of g, which allows for a good degree of malleability and which makes purely environmental models of group differences more tenable. Interestingly, Kan’s characterization of g is quite similar to that of Steve Hsu (e.g., a statistical index of cognitive functioning), but Kan and Hsu draw radically different conclusions about the prospects of searching for g-genes. I think Kan draws the more valid conclusion, a conclusion which Steve missed, when he adopted his g-agnosticism. Were there no underlying biological/genetic g, searching for g-genes would be folly.
The simulations also showed that the general factor of intelligence does not have to represent a realistic (e.g. biological) common cause of individual differences. In our integrated model it is a merely a statistical entity, i.e., an informative summary descriptive. However, as such, general intelligence certainly has utility. Specifically, we consider it to be similar to ’general health’. Like general health is an informative summary descriptive of physical functioning, ’g’ is an informative summary descriptive of cognitive functioning. A distinction between g as a statistically entity, and g as interpreted as a realistic, common cause of individual differences, is not only important theoretically, but also empirically. Consider genetic association and linkage studies of intelligence, for example. So far, the search for genes for general intelligence has met with relatively little success (Deary, Johnson, & Houlihan, 2009; Plomin and Spinath, 2004; Chabris et al., in press). The alternative theories of Dickens and Flynn (2001; Dickens, 2008) and of van der Maas et al. (2006), in which the general factor of intelligence is a statistical entity originating in reciprocal beneficial interactions among cognitive processes or abilities, are able to provide a plausible explanation of this lack of success. In these theories, there are no direct genetic influences general to all abilities. If general intelligence is indeed the outcome of such interactions, the search for specific ‘genetic influences on g‘ is a questionable undertaking (Dolan, Kan, van der Maas, 2008; van der Sluis, Kan & Dolan, 2010), in particular when (1) the genetic determinants of these processes are under mutation selection balance, which means that the process of natural selection reduces genetic variance but cannot deplete all of it because new variation – due to mutations – is continually reintroduced (Penke et al., 2007), and (2) the interactions are nonlinear (e.g. Molenaar, Boomsma, & Dolan, 1993; Kan,Ploeger, Raijmakers, Dolan & van der Maas, 2011).
Anyways, if I get a chance, I will comment on chapter 4, latter.