The Quarterly Review of Biology

This paper was given before the Genetics Section of the Moscow Society of Natural Science on November 26, 1957; before the joint session of the Geographical Society of USSR and the All-Union Botanical Society in Leningrad, December 6, 1957; and in Moscow on January 11, 1958 before the students of the Timiryazev Academy. A review, by I. Grebenschikova and F. Schultz, was printed in Der Zuchter, 28 (4): 161-166 (1958).

The Soviet biophysical literature has been the subject of an extensive and critical review. The subject matter has been subdivided into sections on techniques, effect sof ionizing radiation, effects of light radiation, photosynthesis, effects of ultrasonics, paramagnetic resonance, microorganisms, viruses, cell structure, proteins, nucleic acids, and muscle, nerve, vision and taste. A bibliography of 520 entries is included. The work which has been reviewed covers the best and worst in Soviet science. In general those experiments and concepts in fields that are close to physics are excellent. Examples are the work in paramagnetic resonance, energy transfer mechanism in photosynthesis systems, the properties of structural proteins such as procollagen, and the coding properties of DNA. The average paper concerned with more biological subject matter, such as microorganisms, viruses, and proteins, seems outdated in concept and lacking in controlled experiments or adequate data. Recent reviews (which contain mostly references to Western literature) indicate that Soviet scientists are well acquainted with in Western countries and that the role of DNA as a carrier of genetic information is now fully appreciated.

Pregnancy has commonly been viewed as a cooperative interaction between a mother and her fetus. The effects of natural selection on genes expressed in fetuses, however, may be opposed by the effects of natural selection on genes expressed in mothers. In this sense, a genetic conflict can be said to exist between maternal and fetal genes. Fetal genes will be selected to increase the transfer of nutrients to their fetus, and maternal genes will be selected to limit transfers in excess of some maternal optimum. Thus a process of evolutionary escalation is predicted in which fetal actions are opposed by maternal countermeasures. The phenomenon of genomic imprinting means that a similar conflict exists within fetal cells between genes that are expressed when maternally derived, and genes that are expressed when paternally derived. During implantation, fetally derived cells (trophoblast) invade the maternal endometrium and remodel the endometrial spiral arteries into low-resistance vessels that are unable to constrict. This invasion has three consequences. First, the fetus gains direct access to its mother's arterial blood. Therefore, a mother cannot reduce the nutrient content of blood reaching the placenta without reducing the nutrient supply to her own tissues. Second, the volume of blood reaching the placenta becomes largely independent of control by the local maternal vasculature. Third, the placenta is able to release hormones and other substances directly into the maternal circulation. Placental hormones, including human chorionic gonadotropin (hCG) and human placental lactogen (hPL), are predicted to manipulate maternal physiology for fetal benefit. For example, hPL is proposed to act on maternal prolactin receptors to increase maternal resistance to insulin. If unopposed, the effect of hPL would be to maintain higher blood glucose levels for longer periods after meals. This action, however, is countered by increased maternal production of insulin. Gestational diabetes develops if the mother is unable to mount an adequate response to fetal manipulation. Similarly, fetal genes are predicted to enhance the flow of maternal blood through the placenta by increasing maternal blood pressure. Preeclampsia can be interpreted as an attempt by a poorly nourished fetus to increase its supply of nutrients by increasing the resistance of its mother's peripheral circulation.

The 1890s and the first decades of the twentieth century saw a vigorous debate about the mechanisms of evolutionary change. On one side, August Weismann defended the selectionist hypothesis; on the other, Herbert Spencer defended neo-Lamarckian theory. Supporters of Spencer, notably the American paleontologist and evolutionary theorist Henry Fairfield Osborn, recognized that the questions raised by Weismann and Spencer could only be settled experimentally. They called for the application of experimental methods, and the establishment of a new institution for the purpose of confirming the inheritance of acquired characters. To a great extent, the experimental program championed by Osborn and others was implemented and, although it failed to reveal soft inheritance and was soon eclipsed by Mendelian and chromosomal genetics, it did make significant and lasting contributions to evolutionary biology. Thus the importance of methodological and institutional innovation and theoretical pluralism to the progress of science is illustrated and underscored.

Tithonus asked Aurora for eternal life, when he meant eternal youth. Modern gerontological research makes the same mistake in its preoccupation with death, as if it were a programmed event in an organism's life history. Gerontology ought instead to investigate senescence, the decreasing effectiveness of mechanisms by which adult organisms avoid death or loss of fitness. Such studies should measure rates of decline in a diversity of adaptations and compare them within and between individuals and relate these rates and their correlations to genetic and environmental factors. The death of a studied organism must necessarily end its usefulness in providing valuable data. It is of little scientific significance.

Correlations of social structure, life-history patterns, and ecology among the seventeen species of grouse exemplify some general patterns in the evolution of mating systems among higher vertebrates. The species of grouse differ in the aggregation of displaying males, the permanence of heterosexual affiliations, the contributions of males to parental care, and the breeding sex ratio. Promiscous species (no durable heterosexual affiliation) are probably all polynous (the breeding sex ratio less than unity), but fall into two groups depending on whether the displaying males congregate at leks or disperse relatively evenly. In all of these promiscuous, polygymous species and in three monogramous species, the female cares for the young; dual parental care appears only in one monogamous species. During their first year, the males of polynous species do not mate or mate much less frequently, although females normally breed at one year of age, a situation termed sexual bimaturism. At least among birds and mammal...

Gene flow between different reproductive units such as bacterial plasmids and chromosomes presents unusual problems for evolutionary analysis. Far more than in eukaryotes, reproductive advantages at several levels of selection--genes, transposons, plasmids, cells, and clones--must be considered simultaneously to understand plasmid evolution. No level consistently prevails in conflict situations, and some reproductive units carry genes that restrain their own reproduction or survival, apparently to enhance the reproduction or survival of the higher-level reproductive units that carry them. Despite gene flow between plasmids and chromosomes, genes for certain functions show strong tendencies to occur on plasmids while others consistently occur on chromosomes. Functions generally associated with plasmids are diverse, but all are useful only in locally restricted contexts; it is argued that the selective consequences of the greater horizontal (within generation) transmission of plasmids are responsible for this pattern. The tendency for prokaryote transposons, which are also horizontally mobile, to carry genes similar to those commonly on plasmids supports this argument. The apparent trends in eukaryote plasmids and transposons to lack these same characters also accords with predictions of the local adaptation hypothesis, because genes on these genetic units are generally no more horizontally mobile than chromosomal genes. There are theoretical reasons to expect that plasmid genes tend to evolve more rapidly than chromosomal genes. "The selfish interests of genes have manifestly produced 'vehicles' in the forms of organelles, cells, individuals and yet higher units. If evolution is to predict as well as describe, then selfish interests must be understood in the framework of the constraints and opportunities generated by these 'vehicles'" (Buss, 1987, p. 182).

The review discusses some consequences of the widespread partial uncoupling of the reproduction of organelle DNA from that of nuclear DNA. I propose that in certain circumstances natural selection favors intraorganismal reproductive competition between different varieties of organelle DNA, and in other circumstances selection favors competition between organelle and nuclear DNA. Evidence is marshalled to show that such competition occurs in nature. Situations which would lead to selection for both kinds of competition are described and are shown to be relatively common. A number of examples of apparent competition of predicted kinds are presented. Several testable predictions are made from the theory, and it is shown that the available data are in accord with them. Similar kinds of reproductive competition are predicted to occur in some other symbiotic relationships, and possible examples are presented for two of them: bacterial plasmids and endozoic algae.

Several features of the evolution of eyes and photoreceptors are examined in an effort to explore the relative roles of adaptation and historical and developmental constraints. Optical design shows clear evidence of adaptation, which in some respects approaches optima predictable from physics. The primate fovea, on the other hand, illustrates how adaptation can be channeled by developmental heritage. The primary structures of opsins reveal multiple evolutionary lineages within both Drosophila and humans. The pigments of vertebrae rods comprise a subset of opsins whose evolutionary relationships map onto the phylogeny of the parent species. The evolutionary reasons for why most rod pigments absorb maximally at 500 +/- 10 nm are obscure, as there is no convincing explanation based on adaptation alone. Rods are appropriately distinguished from cones on the basis of which opsin gene is expressed. This criterion is likely to be in conflict with other definitions in phyletic lines (e.g., geckos, snakes) that have long diurnal or nocturnal histories accompanied by loss of one or more opsin genes, followed by a secondary adaptation to life in a different photic environment. Color vision--a generalizable perception associated with the spectral composition of light--is usefully distinguished from wavelength-specific behaviors. The latter are also based on multiple visual pigments and more than one spectral class of receptors but cannot be altered by learning. The distinction is particularly forceful in bees, which exhibit both kinds of behavior. The evolution of primate color vision has been shaped by historical factors involving an extensive period of early mammalian nocturnality. Birds, by contrast, have more elaborate cones and a richer set of visual pigments. Avian color space can be represented in a tetrahedron.

A large fraction, sometimes the largest fraction, of a eukaryotic genome consists of repeated DNA sequences. Copy numbers range from several thousand to millions per diploid genome. All classes of repetitive DNA sequences examined to date exhibit apparently general, but little studied, patterns of "concerted evolution." Historically, concerted evolution has been defined as the nonindependent evolution of repetitive DNA sequences, resulting in a sequence similarity of repeating units that is greater within than among species. This intraspecific homogenization of repetitive sequence arrays is said to take place via the poorly understood mechanisms of "molecular drive." The evolutionary population dynamics of molecular drive remains largely unstudied in natural populations, and thus the potential significance of these evolutionary dynamics for population differentiation is unknown. This review attempts to demonstrate the potential importance of the mechanisms responsible for concerted evolution in the differentiation of populations. It contends that any natural grouping that is characterized by reproductive isolation and limited gene flow is capable of exhibiting concerted evolution of repetitive DNA arrays. Such effects are known to occur in protein and RNA-coding repetitive sequences, as well as in so-called "junk DNA," and thus have important implications for the differentiation and discrimination of natural populations.

Seven general kinds of life cycles are known among crickets; they differ chiefly in overwintering (diapause) stage and number of generations per season, or diapauses per generation. Some species with broad north-south ranges vary in these respects, spannig wholly or in part certain of the gaps between cycles and suggesting how some of the differences orgininated. Species with a particular cycle have predictable responses to photoperiod and temperature regimes that affect behavior, development time, wing length, boyd size, and other characteristics. Some polymorphic tendencies also correlate with habitat permanence, and some are influenced by population density. Genera and subfamilies with several kinds of life cycles usually have proportionately more species in temperate regions than those with but one or two cycles, although numbers of species in all widely distributed groups diminish toward the higher latitudes. The tendency of various field cricket species to become double-cycled at certain latitudes a...

Ribosomal DNA (rDNA) sequences have been aligned and compared in a number of living organisms, and this approach has provided a wealth of information about phylogenetic relationships. Studies of rDNA sequences have been used to infer phylogenetic history across a very broad spectrum, from studies among the basal lineages of life to relationships among closely related species and populations. The reasons for the systematic versatility of rDNA include the numerous rates of evolution among different regions of rDNA (both among and within genes), the presence of many copies of most rDNA sequences per genome, and the pattern of concerted evolution that occurs among repeated copies. These features facilitate the analysis of rDNA by direct RNA sequencing, DNA sequencing (either by cloning or amplification), and restriction enzyme methodologies. Constraints imposed by secondary structure of rRNA and concerted evolution need to be considered in phylogenetic analyses, but these constraints do not appear to impede seriously the usefulness of rDNA. An analysis of aligned sequences of the four nuclear and two mitochondrial rRNA genes identified regions of these genes that are likely to be useful to address phylogenetic problems over a wide range of levels of divergence. In general, the small subunit nuclear sequences appear to be best for elucidating Precambrian divergences, the large subunit nuclear sequences for Paleozoic and Mesozoic divergences, and the organellar sequences of both subunits for Cenozoic divergences. Primer sequences were designed for use in amplifying the entire nuclear rDNA array in 15 sections by use of the polymerase chain reaction; these "universal" primers complement previously described primers for the mitochondrial rRNA genes. Pairs of primers can be selected in conjunction with the analysis of divergence of the rRNA genes to address systematic problems throughout the hierarchy of life.

The positive relationship between a species' geographic distribution and its abundance is one of ecology's most well-documented patterns, yet the causes behind this relationship remain unclear. Although many hypotheses have been proposed to account for distribution-abundance relationships none have attained unequivocal support. Accordingly, the positive association in distribution-abundance relationships is generally considered to be due to a combination of these proposed mechanisms acting in concert. In this review, we suggest that much of the disparity between these hypotheses stems from differences in terminology and ecological point of view. Realizing and accounting for these differences facilitates integration, so that the relative contributions of each mechanism may be evaluated. Here, we review all the mechanisms that have been proposed to account for distribution-abundance relationships, in a framework that facilitates a comparison between them. We identify and discuss the central factors governing the individual mechanisms, and elucidate their effect on empirical patterns.

Since 1813, when Crampton first described the ciliary muscle of the avian eye, there has been little agreement on how birds are able to change the focus of their eyes. Numerous lata studies on the eyes of a variety of bird species contradicted earlier findings or proposed new accommodative mechanisms. The resulting confusion persists today, and a number of significant works on the avian eye perpetuate many of the myths developed during the 1800s. There is little consensus on avian accommodation; the early literature contains many accurate descriptions qi the mechanisms, along with elegant experimental evidence to support them. Much of the early literature, however, is in German and has remained obscure. Further, among the mechanistic descriptions of avian accommodation are many that are incorrect. The current confusion can be attributed in part to the fact that some birds have both corneal and lenticular accommodation. It is unclear to what extent different bird species employ both mechanisms, or depend on one mechanism or the other. These facts, together with the diversity of bird species, their range of visual requirements, and the numerous anatomical differences in their eyes, mab it impossible to describe a single avian mechanism of accommodation. Our own experience in studying accommodation in the chick eye has led us to review the historical literature in an attempt to provide a new foundation for future studies on visual accommodation in birds.

A comprehensive review of women's dietary behavior across the menstrual cycle suggests a drop in caloric intake around the time of ovulation; similar patterns occur in many other mammals. The periovulatory nadir is puzzling, as it is not explicable in terms of changes in the energy budget. Existing explanations in the animal literature operate wholly at the proximate level of analysis and hence do not address this puzzle. In this paper, I offer an ultimate explanation for the periovulatory feeding nadir, arguing that the decrease in the set point for satiation during the fertile period of the female cycle is an adaptation produced by natural selection in order to reduce the motivational salience of goals that compete with those directly or indirectly pertaining to mating. In support of this explanation, I adduce evidence of: a) periovulatory reductions in other ingestive behaviors, and b) periovulatory increases in motor activity and the psychological concomitants thereof.