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Life-span learning: a developmental perspective.

The article discusses learning as embedded processes of development and aging, and as social activity over the life course. The concept of life-span learning is proposed and outlined to discuss these processes as aspects of and propositions in life-span development and aging theory. Life-span learning processes arise and continuously develop in a dynamically complex body, brain, and the mind they support as essential features of development and aging over the life course. Life-span learning processes are established by evolutionary adaptive mechanisms, enriched by challenging environments, and continuously developed in supportive social structures. These ideas are derived from evolutionary biology and psychology, the cognitive sciences, life-span development and aging research, and adult development and learning studies. It is argued that life-span learning activities that challenge the body-mind-brain nexus are indispensable to optimize individual development and aging. Three global interventions and their strategies are discussed that enhance life-span learning: Learning to Learn, Learning for Growth, and Learning for Well-being.

Aging↗

Coevolutionary dynamics in large, but finite populations.

Coevolving and competing species or game-theoretic strategies exhibit rich and complex dynamics for which a general theoretical framework based on finite populations is still lacking. Recently, an explicit mean-field description in the form of a Fokker-Planck equation was derived for frequency-dependent selection with two strategies in finite populations based on microscopic processes [A. Traulsen, J. C. Claussen, and C. Hauert, Phys. Rev. Lett. 95, 238701 (2005)]. Here we generalize this approach in a twofold way: First, we extend the framework to an arbitrary number of strategies and second, we allow for mutations in the evolutionary process. The deterministic limit of infinite population size of the frequency-dependent Moran process yields the adjusted replicator-mutator equation, which describes the combined effect of selection and mutation. For finite populations, we provide an extension taking random drift into account. In the limit of neutral selection, i.e., whenever the process is determined by random drift and mutations, the stationary strategy distribution is derived. This distribution forms the background for the coevolutionary process. In particular, a critical mutation rate uc is obtained separating two scenarios: above uc the population predominantly consists of a mixture of strategies whereas below uc the population tends to be in homogeneous states. For one of the fundamental problems in evolutionary biology, the evolution of cooperation under Darwinian selection, we demonstrate that the analytical framework provides excellent approximations to individual based simulations even for rather small population sizes. This approach complements simulation results and provides a deeper, systematic understanding of coevolutionary dynamics.

Animals↗

Chronoastrobiology: proposal, nine conferences, heliogeomagnetics, transyears, near-weeks, near-decades, phylogenetic and ontogenetic memories.

"Chronoastrobiology: are we at the threshold of a new science? Is there a critical mass for scientific research?" A simple photograph of the planet earth from outer space was one of the greatest contributions of space exploration. It drove home in a glance that human survival depends upon the wobbly dynamics in a thin and fragile skin of water and gas that covers a small globe in a mostly cold and vast universe. This image raised the stakes in understanding our place in that universe, in finding out where we came from and in choosing a path for survival. Since that landmark photograph was taken, new astronomical and biomedical information and growing computer power have been revealing that organic life, including human life, is and has been connected to invisible (non-photic) forces, in that vast universe in some surprising ways. Every cell in our body is bathed in an external and internal environment of fluctuating magnetism. It is becoming clear that the fluctuations are primarily caused by an intimate and systematic interplay between forces within the bowels of the earth--which the great physician and father of magnetism William Gilbert called a 'small magnet'--and the thermonuclear turbulence within the sun, an enormously larger magnet than the earth, acting upon organisms, which are minuscule magnets. It follows and is also increasingly apparent that these external fluctuations in magnetic fields can affect virtually every circuit in the biological machinery to a lesser or greater degree, depending both on the particular biological system and on the particular properties of the magnetic fluctuations. The development of high technology instruments and computer power, already used to visualize the human heart and brain, is furthermore making it obvious that there is a statistically predictable time structure to the fluctuations in the sun's thermonuclear turbulence and thus to its magnetic interactions with the earth's own magnetic field and hence a time structure to the magnetic fields in organisms. Likewise in humans, and in at least those other species that have been studied, computer power has enabled us to discover statistically defined endogenous physiological rhythms and further direct effects that are associated with these invisible geo- and heliomagnetic cycles. Thus, what once might have been dismissed as noise in both magnetic and physiological data does in fact have structure. And we may be at the threshold of understanding the biological and medical meaning and consequences of these patterns and biological-astronomical linkages as well. Structures in time are called chronomes; their mapping in us and around us is called chronomics. The scientific study of chronomes is chronobiology. And the scientific study of all aspects of biology related to the cosmos has been called astrobiology. Hence we may dub the new study of time structures in biology with regard to influences from cosmo- helio- and geomagnetic rhythms chronoastrobiology. It has, of course, been understood for centuries that the movements of the earth in relation to the sun produce seasonal and daily cycles in light energy and that these have had profound effects on the evolution of life. It is now emerging that rhythmic events generated from within the sun itself, as a large turbulent magnet in its own right, can have direct effects upon life on earth. Moreover, comparative studies of diverse species indicate that there have also been ancient evolutionary effects shaping the endogenous chronomic physiological characteristics of life. Thus the rhythms of the sun can affect us not only directly, but also indirectly through the chronomic patterns that solar magnetic rhythms have created within our physiology in the remote past. For example, we can document the direct exogenous effects of given specific solar wind events upon human blood pressure and heart rate. We also have evidence of endogenous internal rhythms in blood pressure and heart rate that are close to but not identical to the period length of rhythms in the solar wind. These were installed genetically by natural selection at some time in the distant geological past. This interpretive model of the data makes the prediction that the internal and external influences on heart rate and blood pressure can reinforce or cancel each other out at different times. A study of extensive clinical and physiological data shows that the interpretive model is robust and that internal and external effects are indeed augmentative at a statistically significant level. Chronoastrobiological studies are contributing to basic science--that is, our understanding is being expanded as we recognize heretofore unelaborated linkages of life to the complex dynamics of the sun, and even to heretofore unelaborated evolutionary phenomena. Once, one might have thought of solar storms as mere transient 'perturbations' to biology, with no lasting importance. Now we are on the brink of understanding that solar turbulences have played a role in shaping endogenous physiological chronomes. There is even documentation for correlations between solar magnetic cycles and psychological swings, eras of belligerence and of certain expressions of sacred or religious feelings. Chronoastrobiology can surely contribute to practical applications as well as to basic science. It can help develop refinements in our ability to live safely in outer space, where for example at the distance of the moon the magnetic influences of the sun will have an effect upon humans unshielded by the earth's native magnetic field. We should be better able to understand these influences as physiological and mechanical challenges, and to improve our estimations of the effects of exposure. Chronoastrobiology moreover holds great promise in broadening our perspectives and powers in medicine and public health right here upon the surface of the earth. Even the potential relevance of chronoastrobiology for practical environmental and agricultural challenges cannot be ruled out at this early stage in our understanding of the apparently ubiquitous effects of magnetism and hence perhaps of solar magnetism on life. The evidence already mentioned that fluctuations in solar magnetism can influence gross clinical phenomena such as rates of strokes and heart attacks, and related cardiovascular variables such as blood pressure and heart rate, should illustrate the point that the door is open to broad studies of clinical implications. The medical value of better understanding magnetic fluctuations as sources of variability in human physiology falls into several categories: 1) The design of improved analytical and experimental controls in medical research. Epidemiological analyses require that the multiple sources causing variability in physiological functions and clinical phenomena be identified and understood as thoroughly as possible, in order to estimate systematic alterations of any one variable. 2) Preventive medicine and the individual patients'care. There are no flat 'baselines', only reference chronomes. Magnetic fluctuations can be shown statistically to exacerbate health problems in some cases. The next step should be to determine whether vulnerable individuals can be identified by individual monitoring. Such vulnerable patients may then discover that they have the option to avoid circumstances associated with anxiety during solar storms, and/or pay special attention to their medication or other treatments. Prehabilitation by self-help can hopefully complement and eventually replace much costly rehabilitation. 3) Basic understanding of human physiological mechanisms. The chronomic organization of physiology implies a much more subtle dynamic integration of functions than is generally appreciated. All three categories of medical value in turn pertain to the challenges for space science of exploring and colonizing the solar system. The earth's native magnetic field acts like an enormous umbrella that offers considerable protection on the surface from harsh solar winds of charged particles and magnetic fluxes. The umbrella becomes weaker with distance from the earth and will offer little protection for humans, other animals, and plants in colonies on the surface of the moon or beyond. Thus it is important before more distant colonization is planned or implemented to better understand those magnetism-related biological- solar interactions that now can be studied conveniently on earth. (ABSTRACT TRUNCATED)

Chronobiology Phenomena↗

Coevolution of an avian host and its parasitic cuckoo.

We use a quantitative genetic model to examine the coevolution of host and cuckoo egg characters (termed "size" as a proxy for general appearance), host discrimination, and host and cuckoo population dynamics. A host decides whether to discard an egg using a comparison of the sizes of the eggs in her nest, which changes as host and cuckoo eggs evolve. Specifically, we assume that the probability that she discards the largest egg in her nest depends on how much larger it is than the second largest egg. This decision rule (i.e., the acceptable difference in egg sizes) also evolves, changing both the chance of successful rejection of a cuckoo egg in parasitized nests and the chance of mistaken rejection of a host egg in both parasitized and unparasitized nests. We find a stable equilibrium for coexistence of the host and cuckoo where there is cuckoo egg mimicry, evolutionary displacement of the host egg away from the cuckoo egg phenotype, and host discrimination against unusual eggs. Both host discrimination and host egg displacement are fairly weak at the equilibrium. Cuckoo egg mimicry, although imperfect, usually evolves more extensively and quickly than the responses of the host. Our model provides evidence for both the evolutionary equilibrium and evolutionary lag hypotheses of host acceptance of parasitic eggs.

Animals↗

Evolution in vitro: analysis of a lineage of ribozymes.

BACKGROUND: Catalytic RNAs, or ribozymes, possessing both a genotype and a phenotype, are ideal molecules for evolution experiments in vitro. A large, heterogeneous pool of RNAs can be subjected to multiple rounds of selection, amplification and mutation, leading to the development of variants that have some desired phenotype. Such experiments allow the investigator to correlate specific genetic changes with quantifiable alterations of the catalytic properties of the RNA. In addition, patterns of evolutionary change can be discerned through a detailed examination of the genotypic composition of the evolving RNA population. RESULTS: Beginning with a pool of 10(13) variants of the Tetrahymena ribozyme, we carried out in vitro evolution experiments that led to the generation of ribozymes with the ability to cleave an RNA substrate in the presence of Ca2+ ions, an activity that does not exist for the wild-type molecule. Over the course of 12 generations, a seven-error variant emerged that has substantial Ca(2+)-dependent RNA-cleavage activity. Advantageous mutations increased in frequency in the population according to three distinct dynamics--logarithmic, linear and transient. Through a comparative analysis of 31 individual variants, we infer how certain mutations influence the catalytic properties of the ribozyme. CONCLUSIONS: In vitro evolution experiments make it possible to elucidate important aspects of both evolutionary biology and structural biochemistry on a reasonable short time scale.

Animals↗

Multiphasic growth models and the evolution of prolonged growth exemplified by human brain evolution.

New models for multiphasic growth are presented. They are illustrated by analysis of brain growth in humans and chimpanzees, and the results are used to test the hypothesis of evolution by proportional growth prolongation: that all descendant growth phases are extended by the same factor while each remains at the ancestral growth rate. The results are consistent with the hypothesis and imply that gross brain weight increase towards humans required change in only one growth parameter: prolongation of the nonlinear ancestral growth phases. The restricted and orderly nature of the developmental changes hints at a basis in few genetic changes. Proportional growth prolongation is of general evolutionary importance because it can reorganize body proportions.

Animals↗

Patterns of resistance to three cereal aphids among wheats in the genus Triticum (Poaceae).

Forty-one accessions of wild and cultivated wheats belonging to 19 Triticum species were tested in the field for resistance to three species of aphids, Rhopalosiphum padi Linnaeus, Sitobion avenae Fabricius and Schizaphis graminum Rondani. Antibiotic resistance was estimated by the increase in biomass of aphids over 21 days on adult plants. Overall resistance was estimated by the plant biomass lost due to aphid infestation. All three species of aphids survived and reproduced on all wheats, and reduced spike biomass compared to uninfested controls. The level of antibiosis varied among wheat species and among accessions, with accessions from three, five and one species showing antibiosis to R. padi, S. avenae and S. graminum, respectively. Overall resistance to the three aphid species was observed in five to seven accessions per aphid species. Resistance was usually specific to one aphid species. The frequency of accessions with antibiosis or overall resistance was associated with the ploidy level of the plant species. Except for overall resistance to R. padi, resistance was highest for diploid species and lowest for hexaploid species. No consistent relationship between resistance and level of domestication was detected. Accessions of the wild wheats, Triticum boeoticum Bois, Triticum tauschii (Coss.) Schmal. and Triticum araraticum Jakubz. exhibited high levels of resistance to aphids, as did Triticum monococcum L. which is derived from T. boeoticum. Nevertheless, individual susceptible or resistant accessions occurred at all levels within the evolutionary tree of wheat.

Analysis of Variance↗

Diversity, endemism, and age distributions in macroevolutionary sources and sinks.

Quantitative tests of historical hypotheses are necessary to advance our understanding of biogeographic patterns of species distributions, but direct tests are often hampered by incomplete fossil or historical records. Here we present an alternative approach in which we develop a dynamic model that allows us to test hypotheses about regional rates of taxon origination, extinction, and dispersal using information on ages and current distributions of taxa. With this model, we test two assumptions traditionally made in the context of identifying regions as "centers of origin"--that regions with high origination rates will have high diversity and high endemism. We find that these assumptions are not necessarily valid. We also develop expressions for the regional age distributions of extant taxa and show that these may yield better insight into regional evolutionary rates. We then apply our model to data on the biogeography and ages of extant genera of marine bivalves and conclude that diversity in polar regions predominantly reflects dispersal of taxa that evolved elsewhere rather than in situ origination-extinction dynamics.

Animals↗

Temporal patterns of genetic variation for resistance and infectivity in a Daphnia-microparasite system.

Theoretical studies have indicated that the population genetics of host-parasite interactions may be highly dynamic. with parasites perpetually adapting to common host genotypes and hosts evolving resistance to common parasite genotypes. The present study examined temporal variation in resistance of hosts and infectivity of parasites within three populations of Daphnia magna infected with the sterilizing bacterium Pasteuria ramosa. Parasite isolates and host clones were collected in each of two years (1997, 1998) from one population; in two other populations, hosts were collected from both years, but parasites from only the first year. We then performed infection experiments (separately for each population) that exposed hosts to parasites from the same year or made combinations involving hosts and parasites from different years. In two populations, patterns were consistent with the evolution of host resistance: either infectivity or the speed with which parasites sterilized hosts declined from 1997 to 1998. In another population, infectivity, virulence, and parasite spore production did not vary among host-year or parasite-year. For this population, we also detected strong within-population genetic variation for resistance. Thus, in this case, genetic variability for fitness-related traits apparently did not translate into evolutionary change. We discuss a number of reasons why genetic change may not occur as expected in parasite-host systems, including negative correlations between resistance and other traits, gene flow, or that the dynamic process itself may obscure the detection of gene frequency changes.

Animals↗

Coevolution to the edge of chaos: coupled fitness landscapes, poised states, and coevolutionary avalanches.

We introduce a broadened framework to study aspects of coevolution based on the NK class of statistical models of rugged fitness landscapes. In these models the fitness contribution of each of N genes in a genotype depends epistatically on K other genes. Increasing epistatic interactions increases the rugged multipeaked character of the fitness landscape. Coevolution is thought of, at the lowest level, as a coupling of landscapes such that adaptive moves by one player deform the landscapes of its immediate partners. In these models we are able to tune the ruggedness of landscapes, how richly intercoupled any two landscapes are, and how many other players interact with each player. All these properties profoundly alter the character of the coevolutionary dynamics. In particular, these parameters govern how readily coevolving ecosystems achieve Nash equilibria, how stable to perturbations such equilibria are, and the sustained mean fitness of coevolving partners. In turn, this raises the possibility that an evolutionary metadynamics due to natural selection may sculpt landscapes and their couplings to achieve coevolutionary systems able to coadapt well. The results suggest that sustained fitness is optimized when landscape ruggedness relative to couplings between landscapes is tuned such that Nash equilibria just tenuously form across the ecosystem. In this poised state, coevolutionary avalanches appear to propagate on all length scales in a power law distribution. Such avalanches may be related to the distribution of small and large extinction events in the record.

Biological Evolution↗

Unified description of evolutionary strategies over continuous parameter spaces.

Several standard processes for searching minima of potential functions, such as thermodynamical strategies (simulated annealing) and biologically motivated self-reproduction strategies, are reduced to Schrödinger eigenvalue problems. The properties of the landscape and the dynamics of the optimization are encoded in the spectrum of the Hamiltonian, which is different in both cases. We discuss some model cases with exact solutions. The connection between thermodynamical strategies and biologically motivated self-reproduction is analyzed and interpreted in the above context. In this way we introduce mixing of both strategies as a new powerful tool of optimization.

Algorithms↗

Darwinian evolution of social behavior: implications for group psychotherapy.

Medicine typically looks to biology for guidance in examining complexity. Application of biological principles to social processes has not been easy. Still, we need not abandon biology in the study of complex social phenomena. Biologists have come to view the study of proximate form and function (revealed by disciplines such as anatomy, psychology and physiology) versus the study of how the form and function ultimately "got to be" (revealed by disciplines such as ethology and sociobiology) as distinct and complementary levels of understanding (Lorenz 1981; Mayr 1982). Though we cannot undertake in this paper explication of the value of understanding the ultimate, as well as the proximate, in studying biological phenomena, interested readers will find a comprehensive discussion in Mayr. The evolutionary principles structuring social interactions are becoming understood and hold promise as a biologically valid system for organizing and guiding the study of complex social behaviors (Essock-Vitale and Fairbanks 1979; Kofoed and MacMillan 1987). Psychological processes have evolved in varying complexities as mechanisms to enable and guide social behavior, increasing the probability that such behavior will be adaptive in a wide variety of circumstances (Trivers 1971). Dynamic and social psychologies describe the proximate internal and interactive intricacies that have resulted from this process but cannot help us understand the goals evolution has "naturally designed" (Thompson 1986) these mechanisms to achieve. The hypothesized drives or instincts underlying most psychological models, often derived from a simplistic understanding of evolutionary theory, are usually simply taken for granted in the development of these models.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Evolution↗

Lessons from the past: biotic recoveries from mass extinctions.

Although mass extinctions probably account for the disappearance of less than 5% of all extinct species, the evolutionary opportunities they have created have had a disproportionate effect on the history of life. Theoretical considerations and simulations have suggested that the empty niches created by a mass extinction should refill rapidly after extinction ameliorates. Under logistic models, this biotic rebound should be exponential, slowing as the environmental carrying capacity is approached. Empirical studies reveal a more complex dynamic, including positive feedback and an exponential growth phase during recoveries. Far from a model of refilling ecospace, mass extinctions appear to cause a collapse of ecospace, which must be rebuilt during recovery. Other generalities include the absence of a clear correlation between the magnitude of extinction and the pace of recovery or the resulting ecological and evolutionary disruption the presence of a survival interval, with few originations, immediately after an extinction and preceding the recovery phase, and the presence of many lineages that persist through an extinction event only to disappear during the subsequent recovery. Several recoveries include numerous missing lineages, groups that are found before the extinction, then latter in the recovery, but are missing during the initial survival-recovery phase. The limited biogeographic studies of recoveries suggest considerable variability between regions.

Animals↗

Group beneficial norms can spread rapidly in a structured population.

Group beneficial norms are common in human societies. The persistence of such norms is consistent with evolutionary game theory, but existing models do not provide a plausible explanation for why they are common. We show that when a model of imitation used to derive replicator dynamics in isolated populations is generalized to allow for population structure, group beneficial norms can spread rapidly under plausible conditions. We also show that this mechanism allows recombination of different group beneficial norms arising in different populations.

Altruism↗

Gene-culture coevolution and sex ratios: the effects of infanticide, sex-selective abortion, sex selection, and sex-biased parental investment on the evolution of sex ratios.

The evolutionary consequences of culturally transmitted practices that cause differential mortality between the sexes, thereby distorting the sex ratio (e.g., female infanticide and sex-selective abortion), are explored using dynamic models of gene-culture coevolution. We investigate how a preference for the sex of offspring may affect the selection of genes distorting the primary sex ratio. Sex-dependent differences in mortality have been predicted to select for a male- or female-biased primary sex ratio, to have no effect, or to favor either under different circumstances. We find that when a mating pair's behavior modifies mortality rates in favor of one sex, but does not change the number of offspring produced in the mating, the primary sex ratio will evolve a bias against the favored sex. However, when the total number of offspring of a mating pair is significantly reduced as a consequence of their prejudice, the primary sex ratio will evolve to favor the preferred sex. These results hold irrespective of whether the sex ratio is distorted by the mother's, the father's or the individual's own autosomal genes. The use of dynamic models of gene-culture coevolution allows us to explore the evolution of alleles which distort the sex ratio, as well as the final equilibrium states of the system. Gene-culture interactions can provide equilibria different from those in purely genetic systems, slow the approach to these equilibria by orders of magnitude, and move the primary (PSR) and the adult sex ratio (ASR) away from any stable equilibrium for hundreds of generations.

Abortion, Induced↗

The mechanisms of lift enhancement in insect flight.

Recent studies have revealed a diverse array of fluid dynamic phenomena that enhance lift production during flapping insect flight. Physical and analytical models of oscillating wings have demonstrated that a prominent vortex attached to the wing's leading edge augments lift production throughout the translational parts of the stroke cycle, whereas aerodynamic circulation due to wing rotation, and possibly momentum transfer due to a recovery of wake energy, may increase lift at the end of each half stroke. Compared to the predictions derived from conventional steady-state aerodynamic theory, these unsteady aerodynamic mechanisms may account for the majority of total lift produced by a flying insect. In addition to contributing to the lift required to keep the insect aloft, manipulation of the translational and rotational aerodynamic mechanisms may provide a potent means by which a flying animal can modulate direction and magnitude of flight forces for manoeuvring flight control and steering behaviour. The attainment of flight, including the ability to control aerodynamic forces by the neuromuscular system, is a classic paradigm of the remarkable adaptability that flying insects have for utilising the principles of unsteady fluid dynamics. Applying these principles to biology broadens our understanding of how the diverse patterns of wing motion displayed by the different insect species have been developed throughout their long evolutionary history.

Animals↗

Retroviral invasion of the koala genome.

Endogenous retroviruses are a common ancestral feature of mammalian genomes with most having been inactivated over time through mutation and deletion. A group of more intact endogenous retroviruses are considered to have entered the genomes of some species more recently, through infection by exogenous viruses, but this event has never been directly proved. We have previously reported koala retrovirus (KoRV) to be a functional virus that is associated with neoplasia. Here we show that KoRV also shows features of a recently inserted endogenous retrovirus that is vertically transmitted. The finding that some isolated koala populations have not yet incorporated KoRV into their genomes, combined with its high level of activity and variability in individual koalas, suggests that KoRV is a virus in transition between an exogenous and endogenous element. This ongoing dynamic interaction with a wild species provides an exciting opportunity to study the process and consequences of retroviral endogenization in action, and is an attractive model for studying the evolutionary event in which a retrovirus invades a mammalian genome.

Animals↗