Conceptions of development and the evolution of behavior

Spontaneous tool use and sensorimotor intelligence in Cebus compared with other monkeys and apes

Spontaneous tool use and sensorimotor intelligence in Cebus were observed to determine whether tool use is discovered fortuitously and learned by trial-and-error or, rather, whether advanced sensorimotor abilities (experimentation and insight) are critical in its ontogeny and evolution.

Game theory and the evolution of behaviour

Evolutionary game theory is a method of analysing the evolution of phenotypes (including types of behaviour) when the fitness of a particular phenotype depends onits frequency in the population. It was first applied to pairwise contests between animals. Such contests usually have some associated asymmetry, in size, prior residence, or age or sex status; the theory predicts that the asymmetry will be used as a cue to settlethe contest, and this is found to be the case. The theory can also be applied when individuals are competing against the population as a whole, or some part of it. In such cases, the evolution of variable behaviour - so-called mixed strategies - is predicted; actual examples of this are given. Game theory can be applied to the evolution of cooperative as well as of antagonistic behaviour. An analysis of the evolution of learning leads to testable predictions about learning behaviour.

Patterns of cortisol reactivity in African-American neonates from low-income environments

Individual differences and stability in patterns of salivary cortisol reactivity were examined in 100 African-American neonates from low-income environments. A pattern of reactivity was defined by the change from prestressor to poststressor cortisol concentrations and the change following the poststressor during a recovery phase. Cortisol reactivity was measured in response to two stressors: the Neonatal Behavioral Assessment Scale (NBAS; T. B. Brazelton & J. K. Nugent) and the routine hospital heels-tick procedure. The use of two stressors allowed an examination of whether patterns of reactivity to different stimuli vary and whether there is individual stability in patterns of cortisol reactivity. Cortisol concentrations changed significantly across the three time points. The magnitude of change during the recovery period differed across stressors. Prestressor cortisol values were associated with cortisol reactivity. Both prestressor cortisol concentrations and pattern of cortisol response were significantly associated within individuals.

Sources of behavioral deviation modeled by early color preferences in quail. I. Behavioral synergism and systemic instability

Differences between population-typical norms of individual variability were studied in five genetic lines of Japanese quail (Coturnix coturnix japonica); two (BL and RL) were bidirectionally selected for early approach preference between blue and red stimuli, two (Hi and Lo) for high and low imprintabilities to the same stimuli, and the fifth (CL) was an unselected genetic control line. Selection resulted in reliably divergent extreme choice performances and imprintabilities and in progressively increasing choice variances in the BL x RL hybrids and the Hi imprintability line. Experimentation tested and rejected the hypotheses that correlated selection of synergistically acting but otherwise extraneous stimulus influences, social interaction effects, or phototactic and short-term learning effects may have been responsible for the observed large variance increases. An alternative interpretation is discussed, according to which directional selection relaxes the genetic buffering and the variance increases reflect the resulting developmental instability of the trait.

Neophenogenesis: a developmental theory of phenotypic evolution

An important task for evolutionary biology is to explain how phenotypes change over evolutionary time. Neo-Darwinian theory explains phenotypic change as the outcome of genetic change brought about by natural selection. In the neo-Darwinian account, genetic change is primary; phenotypic change is a secondary outcome that is often given no explicit consideration at all. In this article, we introduce the concept of neophenogenesis: a persistent, transgenerational change in phenotypes over evolutionary time. A theory of neophenogenesis must encompass all sources of such phenotypic change, not just genetic ones. Both genetic and extra-genetic contributions to neophenogenesis have their effect through the mechanisms of development, and developmental considerations, particularly a rejection of the commonly held distinction between inherited and acquired traits, occupy a central place in neophenogenetic theory. New phenotypes arise because of a change in the patterns of organism-environment interaction that produce development in members of a population. So long as these new patterns of developmental interaction persist, the new phenotype(s) will also persist. Although the developmental mechanisms that produce the novel phenotype may change, as in the process known as "genetic assimilation", such changes are not necessary in order for neophenogenesis to occur, because neophenogenetic theory is a theory of phenotypic, not genetic, change.