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This article presents a potential synthesis between the fitness indicator and life history models of human intelligence through consideration of the phenomena of ability differentiation and integration. The cognitive differentiation-integration effort hypothesis proposes that these effects result from a life history tradeoff between cognitive integration effort, a mating effort component associated with strengthening the positive manifold amongst abilities; and cognitive differentiation effort, a somatic effort component associated with the cultivation of specific abilities. This represents one of two largely independent sources of genetic variance in intelligence; the other is mediated by general fitness and mutation load and is associated with individual differences in levels of 'genetic g'. These two sources (along with a common source of environmental variance) combine to give rise to a variety of cognitive phenotypes characterized by different combinations of high or low levels of 'genetic g' and cognitive specialism or generalism. Fundamental to this model is the assumption that measures of life history speed (K) and g are essentially independent, which is demonstrated via meta-analysis of 10 studies reporting correlations between the variables (ϭ .023, ns, n ϭ 2056). The implications of the model are discussed in an evolutionary, ecological, and developmental context. Seven key predictions are made in the discussion which if tested could provide definitive evidence for the hypothesis.

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The Strategic Differentiation-Integration Effort (SD-IE) hypothesis predicts regulation by life history speed (K) of the magnitudes of the correlations among its components, such that individuals with slower life history strategies exhibit life history traits that are less correlated with each other than individuals with faster life history strategies. This conative differentiation among high-K individuals is proposed to arise due to the elevated social competition in stable, predictable environments faced by these individuals and to facilitate mutualistic rather than antagonistic social interaction strategies via social-ecological nichesplitting and domain-specific resource allocation. We tested the predictions of SD-IE regarding relations among life history traits using the Continuous Parameter Estimation Method on data from two college student convenience samples, one all-female sample (N=382) and one mixed-sex sample (N=205), as well as two nationally-representative samples of the US population, the MIDUS (National Survey of Midlife Development in the United States, N=2080) and the NLSY (National Longitudinal Survey of Youth, N=5082). The predicted SD-IE effects were statistically significant and in the expected negative direction among most indicators of the lower-order slow life history factors and among all indicators of the single higher-order slow life history Super-K factor.

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Response to mechanical force is a well characterised phenomenon in eukaryotic organisms, helping to organise multicellular structures. Mechanotactic responses have only rarely been observed in prokaryotic taxa. This work reports on a morphological change due to variations in applied force and surface structure by Bacillus mycoides Flügge. B. mycoides is a ubiquitous soil organism well known among microbiologists for its characteristic spreading colony morphology. An apparent mechanotactic response is elicited by physical deformation of the gel media on which B.mycoides is growing, including applied forces of compression or tension. Variations in the surface such as curvature produced by casting the agar gel in the presence of curved objects also elicited the change. The morphological change in B.mycoides colonies associated with the application of force manifests as a pattern of parallel rhizoid filaments perpendicular to compressing force and parallel to stretching force in the agar medium. The phenomenon is most clearly demonstrated by reversible changes in the orientation of B. mycoides filaments during time-lapse microscopy.

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