Recent studies on neural pathways in a broad spectrum of vertebrates suggest that, in addition to migration and an increase in the number of certain select neurons, a significant aspect of neural evolution is a “parcellation” (segregation-isolation) process that involves the loss of selected connections by the new aggregates. A similar process occurs during ontogenetic development. These findings suggest that in many neuronal systems axons do not invade unknown territories during evolutionary or ontogenetic development but follow in their ancestors' paths to their ancestral targets; if the connection is later lost, it reflects the specialization of the circuitry.

The pattern of interspecific variability suggests (1) that overlap of circuits is a more common feature in primitive (generalized) than in specialized brain organizations and (2) that most projections, such as the retinal, thalamotelencephalic, corticotectal, and tectal efferent ones, were bilateral in the primitive condition. Specialization of these systems in some vertebrate groups has involved the selective loss of connections, resulting in greater isolation of functions. The parcellation process may also play an important role in cell diversification.

The parcellation process as described here is thought to be one of several underlying mechanisms of evolutionary and ontogenetic differentiation.

Although the use of ECT has declined dramatically from its inception, this decrease has recently shown signs of leveling out because of ECT's powerful therapeutic effect in severely ill depressed individuals who either do not respond to pharmacologic alternatives or are too ill to tolerate a relatively lengthy drug trial. Notwithstanding its therapeutic benefits, ECT has also remained a controversial treatment modality, particularly in the eye of the public. Given the unsavory qualities associated with the word “electroconvulsive,” claims of possible, probable, or even certain brain damage with ECT have easily found listeners. A careful, nonselective assessment of data covering the areas of pathology, radiology, electrophysiology, biochemistry, and neuropsychology leads both to certain conclusions and to certain unanswered questions. ECT is not the devastating purveyor of wholesale brain damage that some of its detractors claim. For the typical individual receiving ECT, no detectable correlates of irreversible brain damage appear to occur. Still, there remains the possibility that either subtle, objectively undetectable persistent deficits, particularly in the area of autobiographic memory function, occur, or that a rarely occurring syndrome of more pervasive persistent deficits related to ECT use may be present. Clearly, more research directed toward answering these questions needs to be carried out so that the role of ECT can be more rigorously defined. While such research is pending, however, we cannot expect that the conditions that predispose to clinical referrals for ECT will disappear. Given the misery, anguish, and risk of death by suicide, starvation, or debilitation associated with severe depressive illness, for example, it still appears that ECT, at least for the present, must continue to be available.

It is hypothesized that creole languages are largely invented by children and show fundamental similarities, which derive from a biological program for language. The structures of Hawaiian Pidgin and Hawaiian Creole are contrasted, and evidence is provided to show that the latter derived from the former in a single generation. A realistic model of the processes of Creole formation shows how several specific historical and demographic factors interacted to restrict, in varying degrees, the access of pidgin speakers to the dominant language, and hence the nature of input to the children of those speakers. It is shown that the resulting similarities of Creole languages derive from a single grammar with a restricted list of categories and operations. However, grammars of individual Creoles will differ from this grammar to a varying extent: The degree of difference will correlate very closely with the quantity of dominant-language input, which in turn is controlled by extralinguistic factors. Alternative explanations of the above phenomena are surveyed, in particular, substratum theory and monogenesis: Both are found inadequate to account for the facts. Primary acquisition is examined in light of the general hypothesis, and it is suggested that the bioprogram provides a skeletal model of language which the child can then readily convert into the target language. Cases of systematic error and precocious learning provide indirect support for the hypothesis. Some conjectures are made concerning the evolutionary origins of the bioprogram and what study of Creoles and related topics might reveal about language origins.

Human behavior is the joint product of (i) contingencies of survival responsible for natural selection, and (ii) contingencies of reinforcement responsible for the repertoires of individuals, including (iii) the special contingencies maintained by an evolved social environment. Selection by consequences is a causal mode found only in living things, or in machines made by living things. It was first recognized in natural selection: Reproduction, a first consequence, led to the evolution of cells, organs, and organisms reproducing themselves under increasingly diverse conditions. The behavior functioned well, however, only under conditions similar to those under which it was selected.

Reproduction under a wider range of consequences became possible with the evolution of processes through which organisms acquired behavior appropriate to novel environments. One of these, operant conditioning, is a second kind of selection by consequences: New responses could be strengthened by events which followed them. When the selecting consequences are the same, operant conditioning and natural selection work together redundantly. But because a species which quickly acquires behavior appropriate to an environment has less need for an innate repertoire, operant conditioning could replace as well as supplement the natural selection of behavior.

Social behavior is within easy range of natural selection, because other members are one of the most stable features of the environment of a species. The human species presumably became more social when its vocal musculature came under operant control. Verbal behavior greatly increased the importance of a third kind of selection by consequences, the evolution of social environments or cultures. The effect on the group, and not the reinforcing consequences for individual members, is responsible for the evolution of culture.