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  • 1.
    Aguilar, Elliot
    et al.
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. City University of New York, United States.
    Ghirlanda, Stefano
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. City University of New York, United States; Brooklyn College, United States.
    Modeling the genealogy of a cultural trait2015Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 101, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mathematical study of genealogies has yielded important insights in population biology, such as the ability to estimate the time to the most recent common ancestor (MRCA) of a sample of genetic sequences or of a group of individuals. Here we introduce a model of cultural genealogies that is a step toward answering similar questions for cultural traits. In our model individuals can inherit from a variable, potentially large number of ancestors, rather than from a fixed, small number of ancestors (one or two) as is typical of genetic evolution. We first show that, given a sample of individuals, a cultural common ancestor does not necessarily exist. We then introduce a related concept: the most recent unique ancestor (MRUA), i.e., the most recent single individual who is the earliest cultural ancestor of the sample. We show that, under neutral evolution, the time to the MRUA can be staggeringly larger than the time to MRCA in a single ancestor model, except when the average number of learning opportunities per individuals is small. Our results point out that the properties of cultural genealogies may be very different from those of genetic genealogies, with potential implications for reconstructing the histories of cultural traits.

  • 2.
    Enquist, Magnus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Ghirlanda, Stefano
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Jarrick, Arne
    Stockholms universitet, Humanistiska fakulteten, Historiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Wachtmeister, C-A
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Why does human culture increase exponentially?2008Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 74, nr 1, s. 46-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Historical records show that culture can increase exponentially in time, e.g., in number of poems, musical works, scientific discoveries. We model how human capacities for creativity and cultural transmission may make such an increase possible, suggesting that: (1) creativity played a major role at the origin of human culture and for its accumulation throughout history, because cultural transmission cannot, on its own, generate exponentially increasing amounts of culture; (2) exponential increase in amount of culture can only occur if creativity is positively influenced by culture. The evolution of cultural transmission is often considered the main genetic bottleneck for the origin of culture, because natural selection cannot favor cultural transmission without any culture to transmit. Our models suggest that an increase in individual creativity may have been the first step toward human culture, because in a population of creative individuals there may be enough non-genetic information to favor the evolution of cultural transmission.

  • 3.
    Ghirlanda, Stefano
    et al.
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. Brooklyn College, USA.
    Enquist, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Lind, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Coevolution of intelligence, behavioral repertoire, and lifespan2014Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 91, s. 44-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Across many taxa, intriguing positive correlations exist between intelligence (measured by proxy as encephalization), behavioral repertoire size, and lifespan. Here we argue, through a simple theoretical model, that such correlations arise from selection pressures for efficient learning of behavior sequences. We define intelligence operationally as the ability to disregard unrewarding behavior sequences, without trying them out, in the search for rewarding sequences. We show that increasing a species' behavioral repertoire increases the number of rewarding behavior sequences that can be performed, but also the time required to learn such sequences. This trade-off results in an optimal repertoire size that decreases rapidly with increasing sequence length. Behavioral repertoire size can be increased by increasing intelligence or lengthening the lifespan, giving rise to the observed correlations between these traits.

  • 4.
    Ghirlanda, Stefano
    et al.
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. Brooklyn College, USA.
    Enquist, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Lind, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Corrigendum to "Coevolution of intelligence, behavioral repertoire, and lifespan" [Theoret. Popul. Biol. 91 (2014) 44–49]2014Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 97, s. 57-57Artikel i tidskrift (Övrigt vetenskapligt)
  • 5.
    Ghirlanda, Stefano
    et al.
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Enquist, Magnus
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Perc, Matjaz
    Physics Department, University of Maribor, Slovenia.
    Sustainability of culture-driven population dynamics2010Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 77, nr 3, s. 181-188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider models of the interactions between human population dynamics and cultural evolution, asking whether they predict sustainable or unsustainable patterns of growth. Phenomenological models predict either unsustainable population growth or stabilization in the near future. The latter prediction, however, is based on extrapolation of current demographic trends and does not take into account causal processes of demographic and cultural dynamics. Most existing causal models assume (or derive from simplified models of the economy) a positive feedback between cultural evolution and demographic growth, and predict unlimited growth in both culture and population. We augment these models taking into account that: (1) cultural transmission is not perfect, i.e., culture can be lost; (2) culture does not always promote population growth. We show that taking these factors into account can cause radically different model behavior, such as population extinction rather than stability, and extinction rather than growth. We conclude that all models agree that a population capable of maintaining a large amount of culture, including a powerful technology, runs a high risk of being unsustainable. We suggest that future work must address more explicitly both the dynamics of resource consumption and the cultural evolution of beliefs implicated in reproductive behavior (e.g., ideas about the preferred family size) and in resource use (e.g., environmentalist stances).

  • 6.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Jorde, Per Erik
    Ryman, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Quasi equilibrium approximations of the fixation index under neutrality: The finite and infinite island models2013Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 84, s. 9-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fixation index FST and the coefficient of gene differentiation GST are analyzed for the finite island model under short time spans, ignoring mutations. Dividing the reproduction cycle into the three steps–gamete formation, fertilization, and migration–we develop a new approach for computing quasi equilibrium formulas for FST (and GST). Our formulas generalize earlier ones and reveal that the equilibrium value of FST is influenced not only by the migration rate and local effective population size, Ne, but also by the local census size N, particularly so when the migration rate is high. The order of migration and fertilization is found to have a smaller effect on FST. A major advantage compared to previous approaches is that stochastic allele frequency of migrants is easily accommodated, thereby avoiding underestimation of FST for large migration rates.

  • 7.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Laikre, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Ryman, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Effective sizes and time to migration-drift equilibrium in geographically subdivided populations2016Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 112, s. 139-156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many versions of the effective population size (N-e) exist, and they are important in population genetics in order to quantify rates of change of various characteristics, such as inbreeding, heterozygosity, or allele frequencies. Traditionally, N-e was defined for single, isolated populations, but we have recently presented a mathematical framework for subdivided populations. In this paper we focus on diploid populations with geographic subdivision, and present new theoretical results. We compare the haploid and diploid versions of the inbreeding effective size (N-ei) with novel expression for the variance effective size (N-ev), and conclude that for local populations N-ev is often much smaller than both versions of Nei, whenever they exist. Global N(ev)of the metapopulation, on the other hand, is close to the haploid Net and much larger than the diploid Nei. We introduce a new effective size, the additive genetic variance effective size Neill', which is of particular interest for long term protection of species. It quantifies the rate at which additive genetic variance is lost and we show that this effective size is closely related to the haploid version of Nei. Finally, we introduce a new measure of a population's deviation from migration-drift equilibrium, and apply it to quantify the time it takes to reach this equilibrium. Our findings are of importance for understanding the concept of effective population size in substructured populations and many of the results have applications in conservation biology.

  • 8.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Olsson, Fredrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Laikre, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Ryman, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Metapopulation inbreeding dynamics, effective size and subpopulation differentiation-A general analytical approach for diploid organisms2015Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 102, s. 40-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Motivated by problems in conservation biology we study genetic dynamics in structured populations of diploid organisms (monoecious or dioecious). Our analysis provides an analytical framework that unifies substantial parts of previous work in terms of exact identity by descent (IBD) and identity by state (IBS) recursions. We provide exact conditions under which two structured haploid and diploid populations are equivalent, and some sufficient conditions under which a dioecious diploid population can be treated as a monoecious diploid one. The IBD recursions are used for computing local and metapopulation inbreeding and coancestry effective population sizes and for predictions of several types of fixation indices over different time horizons.

  • 9.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Tyvand, Peder A.
    Local fluctuations of genetic processes defined on two time scales, with applications to effective size estimation2020Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 131, s. 79-99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we develop a general framework for how the genetic composition of a structured population with strong migration between its subunits, evolves over time. The dynamics is described in terms of a vector-valued Markov process of allele, genotype or haplotype frequencies that varies on two time scales. The more rapid changes are random fluctuations in terms of a multivariate autoregressive process, around a quasi equilibrium fix point, whereas the fix point itself varies more slowly according to a diffusion process, along a lower-dimensional subspace. Under mild regularity conditions, the fluctuations have a magnitude inversely proportional to the square root of the population size N, and hence can be used to estimate a broad class of genetically effective population sizes N-e, with genetic data from one time point only. In this way we are able to unify a number of existing notions of effective size, as well as proposing new ones, for instance one that quantifies the extent to which genotype frequencies fluctuate around Hardy-Weinberg equilibrium. (C) 2019 Elsevier Inc. All rights reserved.

  • 10.
    Olsson, Fredrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Estimation of the variance effective population size in age structured populations2015Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 101, s. 9-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The variance effective population size for age structured populations is generally hard to estimate and the temporal method often gives biased estimates. Here, we give an explicit expression for a correction factor which, combined with estimates from the temporal method, yield approximately unbiased estimates. The calculation of the correction factor requires knowledge of the age specific offspring distribution and survival probabilities as well as possible correlation between survival and reproductive success. In order to relax these requirements, we show that only first order moments of these distributions need to be known if the time between samples is large, or individuals from all age classes which reproduce are sampled. A very explicit approximate expression for the asymptotic coefficient of standard deviation of the estimator is derived, and it can be used to construct confidence intervals and optimal ways of weighting information from different markers. The asymptotic coefficient of standard deviation can also be used to design studies and we show that in order to maximize the precision for a given sample size, individuals from older age classes should be sampled since their expected variance of allele frequency change is higher and easier to estimate. However, for populations with fluctuating age class sizes, the accuracy of the method is reduced when samples are taken from older age classes with high demographic variation. We also present a method for simultaneous estimation of the variance effective and census population size.

  • 11.
    Olsson, Fredrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Laikre, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Ryman, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Characteristics of the variance effective population size over time using an age structured model with variable size2013Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 90, s. 91-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The variance effective population size (N-ev) is a key concept in population biology, because it quantifies the microevolutionary process of random genetic drift, and understanding the characteristics of N-ev is thus of central importance. Current formulas for Nev for populations with overlapping generations weight age classes according to their reproductive values (i.e. reflecting the contribution of genes from separate age classes to the population growth) to obtain a correct measure of genetic drift when computing the variance of the allele frequency change over time. In this paper, we examine the effect of applying different weights to the age classes using a novel analytical approach for exploring N-ev. We consider a haploid organism with overlapping generations and populations of increasing, declining, or constant expected size and stochastic variation with respect to the number of individuals in the separate age classes. We define Nov, as a function of how the age classes are weighted, and of the span between the two points in time, when measuring allele frequency change. With this model, time profiles for N-ev can be calculated for populations with various life histories and with fluctuations in life history composition, using different weighting schemes. We examine analytically and by simulations when Nei, using a weighting scheme with respect to reproductive contribution of separate age classes, accurately reflect the variance of the allele frequency change due to genetic drift over time. We show that the discrepancy of N-ev, calculated with reproductive values as weights, compared to when individuals are weighted equally, tends to a constant when the time span between the two measurements increases. This constant is zero only for a population with a constant expected population size. Our results confirm that the effect of ignoring overlapping generations, when empirically assessing Nell from allele frequency shifts, gets smaller as the time interval between samples increases. Our model has empirical applications including assessment of (i) time intervals necessary to permit ignoring the effect of overlapping generations for N-ev estimation by means of the temporal method, and (ii) effects of life table manipulation on N-ev over varying time periods.

  • 12.
    Strimling, Pontus
    et al.
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Sjöstrand, Jonas
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Enquist, Magnus
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning. Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen.
    Eriksson, Kimmo
    Stockholms universitet, Humanistiska fakulteten, Centrum för evolutionär kulturforskning.
    Accumulation of independent cultural traits2009Ingår i: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 76, nr 2, s. 77-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In a species capable of (imperfect) social learning, how much culture can a population of a given size carry? And what is the relationship between the individual and the population? In the first study of these novel questions, here we develop a mathematical model of the accumulation of independent cultural traits in a finite population with overlapping generations.

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