Evolutionary Demography

Life expectancy is increasing in most countries and has exceeded 80 in several, as low-mortality nations continue to make progress in averting deaths. The health and economic implications of mortality reduction have been given substantial attention, but the observed malleability of human mortality has not been placed in a broad evolutionary context. We quantify the rate and amount of mortality reduction by comparing a variety of human populations to the evolved human mortality profile, here estimated as the average mortality pattern for ethnographically observed hunter-gatherers. We show that human mortality has decreased so substantially that the difference between hunter-gatherers and today's lowest mortality populations is greater than the difference between huntergatherers and wild chimpanzees. The bulk of this mortality reduction has occurred since 1900 and has been experienced by only about 4 of the roughly 8,000 human generations that have ever lived. Moreover, mortality improvement in humans is on par with or greater than the reductions in mortality in other species achieved by laboratory selection experiments and endocrine pathway mutations. This observed plasticity in age-specific risk of death is at odds with conventional theories of aging. biodemography | cross-species comparison | life history evolution | phenotypic plasticity | human lifespan

There persist two widely held but mutually inconsistent views on the evolution of post-fertile lifespan of human females. The first, prevalent within anthropology, sees post-fertile lifespan (PFLS) in the light of adaptive processes, focusing on the social and economic habits of humans that selected for a lengthy PFLS. 1-3 This view rests on the assumption that human PFLS is distinct from that of other species, and focuses on quantifying the selective causes and consequences of that difference. The second view, prevalent within gerontology and comparative biology, emphasizes that PFLS is a phylogenetically widespread trait 4-6 or that human PFLS is predictable based on life-history allometries. 7 In this view, human PFLS is part of a broad cross-species pattern and its genesis cannot, therefore, rely on human-specific traits. Those who advocate the second view have questioned the "special pleading" for human specific explanations of PFLS, 4 and have argued that human PFLS is quantitatively greater but not qualitatively different than PFLS in many other animals. 5,8 Papers asking whether human PFLS is explained by the importance of mothers more than grandmothers, whether paternal or maternal grandparents have more of an effect on child survival, or who is providing the excess calories are associated with the first view that assumes the need to explain the existence of human PFLS on the basis of a uniquely human socioecology. Anthropologists largely see human PFLS as derived, while comparative gerontologists point to evidence that it is one instance of a ubiquitous cross-species pattern. The two groups generally occupy non-overlapping research circles, in terms of conferences and journals, and therefore interact little enough to largely avoid the need to reconcile their views, allowing the persistence of misconceptions in each field. Our goal is to identify and address the most important of these misconceptions and thereby make clear that both of these seemingly incongruent views contain valid points. We argue that two distinct but related traits have been lumped together under the same concept of "post-reproductive lifespan," one (post-fertile viability) that is tremendously widespread and another (a post-fertile life stage) that is derived to hominins, and that the differences and connections between these two traits are necessary for understanding human life-history evolution.

• A novel method for building multitrait population projection matrices is proposed. • Asymptotic properties of multitrait matrices are explored. • A new evolutionary demography tool, the trait level analysis, is proposed. • Trait level analysis sheds light on effect of traits on multitrait dynamics. • A parity–fertility–fecundity model reveals the potential of trait level analysis. a b s t r a c t In most matrix population projection models, individuals are characterized according to, usually, one or two traits such as age, stage, size or location. A broad theory of multitrait population projection matrices (MPPMs) incorporating larger number of traits was long held back by time and space computational complexity issues. As a consequence, no study has yet focused on the influence of the structure of traits describing a life-cycle on population dynamics and life-history evolution. We present here a novel vector-based MPPM building methodology that allows to computationally-efficiently model populations characterized by numerous traits with large distributions, and extend sensitivity analyses for these models. We then present a new method, the trait level analysis consisting in folding an MPPM on any of its traits to create a matrix with alternative trait structure (the number of traits and their characteristics) but similar asymptotic properties. Adding or removing one or several traits to/from the MPPM and analyzing the resulting changes in spectral properties, allows investigating the influence of the trait structure on the evolution of traits. We illustrate this by modeling a 3-trait (age, parity and fecundity) population designed to investigate the implications of parity–fertility trade-offs in a context of fecundity heterogeneity in humans. The trait level analysis, comparing models of the same population differing in trait structures, demonstrates that fertility selection gradients differ between cases with or without parity–fertility trade-offs. Moreover it shows that age-specific fertility has seemingly very different evolutionary significance depending on whether heterogeneity is accounted for. This is because trade-offs can vary strongly in strength and even direction depending on the trait structure used to model the population.

Este artigo apresenta os processos que envolvem a migração subsaariana para Espanha e a haitiana para o Brasil, passando pelos fatores que impulsionam os deslocamentos, as rotas migratórias utilizadas, a inserção social e laboral desses migrantes e o momento das políticas migratórias em cada um dos países de destino, ressaltando as semelhanças e algumas diferenças em cada um desses processos. O objetivo é demonstrar que longe de se constituírem numa ameaça invasora, mais bem são vítimas de um sistema que produz exclusão e exploração, que nos casos de subsaarianos e haitianos se amplifica pelos componentes da discriminação e racismo.

The demographic rates of most organisms are supported by the consumption of food energy, which is used to produce new biomass and fuel physiological processes. Unlike other species, modern humans use 'extra-metabolic' energy sources acquired independent of physiology, which also influence demographics. We ask whether the amount of extra-metabolic energy added to the energy budget affects demographic and life history traits in a predictable way. Currently it is not known how human demographics respond to energy use, and we characterize this response using an allometric approach. All of the human life history traits we examine are significant functions of per capita energy use across industrialized populations. We find a continuum of traits from those that respond strongly to the amount of extra-metabolic energy used, to those that respond with shallow slopes. We also show that the differences in plasticity across traits can drive the net reproductive rate to below-replacement levels.

The negative wealth–fertility relationship brought about by market integration remains a puzzle to classic evolutionary models. Evolutionary ecologists have argued that this phenomenon results from both stronger trade-offs between reproductive and socioeconomic success in the highest
social classes and the comparison of groups rather than individuals. Indeed, studies in contemporary low fertility settings have typically used aggregated samples that may mask positive wealth–fertility relationships. Furthermore,
while much evidence attests to trade-offs between reproductive and socioeconomic success, few studies have explicitly tested the idea that such constraints are intensified by market integration. Using data from Mongolia, a post-socialist nation that underwent mass privatization, we examine
wealth–fertility relationships over time and across a rural–urban gradient. Among post-reproductive women, reproductive fitness is the lowest in urban areas, but increases with wealth in all regions. After liberalization, a
demographic–economic paradox emerges in urban areas: while educational attainment negatively impacts female fertility in all regions, education uniquely provides socioeconomic benefits in urban contexts. As market integration progresses, socio-economic returns to education increase and women who limit their reproduction to pursue education get wealthier. The
results support the view that selection favoured mechanisms that respond to opportunities for status enhancement rather than fertility maximization.

Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be similar in value for very different life histories. However, humans have some unique ecological characteristics that may alter LRE, such as the long post-reproductive lifespan, lengthy juvenile period and the cooperative nature of human foraging and reproduction. We calculate LRE for natural fertility human populations, compare the findings to other mammals and discuss the implications for human life-history evolution. We find that human life-history traits combine to yield the theoretically predicted value (approx. 1.4). Thus, even with the subsidized energy budget and uniqueness of the adult lifespan, human reproductive strategies converge on the same optimal value of LRE. This suggests that the fundamental demographic variables contained in LRE trade-off against one another in a predictable and highly constrained manner.

... The corollary of this is that populations are often unpredictable, and that 'the devil is in the detail' (Clutton-Brock & Coulson 2002) when it ... to the results of a density-dependent and stochastic analysis (Caswell 2001), but this is certainly not invariably true (Grant & Benton 2003). ...

The ambivalent attitude of demographers towards the formulating and applying of scientific theories is a long-term issue. So far, the strong point of demography has been in precise empirical research and analysis, not in the formulation of scientific theories. The most widespread theoretical platform in demography is the theory of the Demographic revolution/Demographic transition. Some researchers argue that it is not a scientific theory ad litteram (in the true sense of the word). In the last thirty years, several demographers have turned their attention to the theory of evolution by natural selection. The research
interest of demography and evolutionary sciences intersects in several areas. In addition, in the last two decades, the evolutionary approach has begun to be systematically applied in demography. The aim of the text is to illustrate how the theoretical and analytical concepts of evolutionary sciences (both evolutionary biology and evolutionary anthropology) can be used in demographic research.

‘Demographic transition theory’ assumes that fertility decline is irreversible. This commonly held assumption is based on observations of recent and historical reductions in fertility that accompany modernization and declining mortality. The irreversibility assumption, however, is highly suspect from an evolutionary point of view, because demographic traits are at least partially influenced by genetics and are responsive to social and ecological conditions. Nonetheless, an inevitable shift from high mortality and fertility to low mortality and fertility is used as a guiding framework for projecting human population sizes into the future. This paper reviews some theoretical and empirical evidence suggesting that the assumption of irreversibility is ill-founded, at least without considerable development in theory that incorporates
evolutionary and ecological processes. We offer general propositions
for how fertility could increase in the future, including natural selection on high fertility variants, the difficulty of maintaining universal norms and
preferences in a large, diverse and economically differentiated population, and the escalating resource demands of modernization.