Human uniqueness? Life history diversity among small-scale societies and chimpanzees

Background Humans life histories have been described as “slow”, patterned by slow growth, delayed maturity, and long life span. While it is known that human life history diverged from that of a recent common chimpanzee-human ancestor some ~4–8 mya, it is unclear how selection pressures led to these distinct traits. To provide insight, we compare wild chimpanzees and human subsistence societies in order to identify the age-specific vital rates that best explain fitness variation, selection pressures and species divergence. Methods We employ Life Table Response Experiments to quantify vital rate contributions to population growth rate differences. Although widespread in ecology, these methods have not been applied to human populations or to inform differences between humans and chimpanzees. We also estimate correlations between vital rate elasticities and life history traits to investigate differences in selection pressures and test several predictions based on life history theory. Results Chimpanzees’ earlier maturity and higher adult mortality drive species differences in population growth, whereas infant mortality and fertility variation explain differences between human populations. Human fitness is decoupled from longevity by postreproductive survival, while chimpanzees forfeit higher potential lifetime fertility due to adult mortality attrition. Infant survival is often lower among humans, but lost fitness is recouped via short birth spacing and high peak fertility, thereby reducing selection on infant survival. Lastly, longevity and delayed maturity reduce selection on child survival, but among humans, recruitment selection is unexpectedly highest in longer-lived populations, which are also faster-growing due to high fertility. Conclusion Humans differ from chimpanzees more because of delayed maturity and lower adult mortality than from differences in juvenile mortality or fertility. In both species, high child mortality reflects bet-hedging costs of quality/quantity tradeoffs borne by offspring, with high and variable child mortality likely regulating human population growth over evolutionary history. Positive correlations between survival and fertility among human subsistence populations leads to selection pressures in human subsistence societies that differ from those in modern populations undergoing demographic transition.

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Human uniqueness illustrated by life history diversity among small-scale societies and chimpanzees

10.1101/2020.09.02.280602 ◽

2020 ◽

Author(s):

Raziel J. Davison ◽

Michael D. Gurven

Keyword(s):

Life History ◽

Population Growth ◽

Child Mortality ◽

Species Differences ◽

Adult Mortality ◽

Natural Fertility ◽

Infant Survival ◽

Selection Pressures ◽

Positive Correlations ◽

Human Subsistence

AbstractBackgroundWe compare life histories and selection forces among chimpanzees and human subsistence societies in order to identify the age-specific vital rates that best explain fitness variation, selection pressures and species divergence.MethodsWe employ Life Table Response Experiments that quantify vital rate contributions to population growth rate differences. Although widespread in ecology, these methods have not been applied to human populations or to look at species differences among humans and chimpanzees. We also estimate correlations between vital rate elasticities and life history traits to investigate differences in selection pressures and test predictions of life history theory.ResultsChimpanzees’ earlier maturity and higher adult mortality drive species differences, whereas infant mortality and fertility variation drive differences among humans. Human fitness is decoupled from longevity by postreproductive survival, while chimpanzees forfeit higher potential lifetime fertility due to adult mortality attrition. Infant survival is often lower among humans, but lost fitness is recouped via short birth spacing and high peak fertility, thereby reducing selection on infant survival. Lastly, longevity and delayed maturity reduce selection on child survival, but among humans, recruitment selection is unexpectedly highest in longer-lived populations, which are also faster-growing due to high fertility.ConclusionHumans differ from chimpanzees more because of delayed maturity and adult mortality than child mortality or fertility rates. In both species, high child mortality reflects bet-hedging costs of quality/quantity tradeoffs borne by offspring, with high and variable child mortality likely regulating human population growth over evolutionary history. Among human subsistence societies, positive correlations between survival and natural fertility lead selection pressures in human subsistence societies to differ from modern populations undergoing demographic transition, due in part to positive correlations between longevity and natural fertility and negative correlations between recruitment elasticity and reproductive effort.

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Demography of Xenosaurus platyceps (Squamata: Xenosauridae): a comparison between tropical and temperate populations

Amphibia-Reptilia ◽

10.1163/156853808784124992 ◽

2008 ◽

Vol 29 (2) ◽

pp. 245-256 ◽

Cited By ~ 6

Author(s):

Carissa Jones ◽

Isaac Rojas-González ◽

Julio Lemos-Espinal ◽

Jaime Zúñiga-Vega

Keyword(s):

Life History ◽

Population Growth ◽

Adult Mortality ◽

Life History Strategies ◽

Relative Importance ◽

Theoretical Frameworks ◽

Population Growth Rates ◽

Relative Contribution ◽

Two Populations ◽

Average Fitness

Abstract There appears to be variation in life-history strategies even between populations of the same species. For ectothermic organisms such as lizards, it has been predicted that demographic and life-history traits should differ consistently between temperate and tropical populations. This study compares the demographic strategies of a temperate and a tropical population of the lizard Xenosaurus platyceps. Population growth rates in both types of environments indicated populations in numerical equilibrium. Of the two populations, we found that the temperate population experiences lower adult mortality. The relative importance (estimated as the relative contribution to population growth rate) of permanence and of the adult/reproductive size classes is higher in the temperate population. In contrast, the relative importance for average fitness of fecundity and growth is higher in the tropical population. These results are consistent with the theoretical frameworks about life-historical differences among tropical and temperate lizard populations.

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Periodic catastrophes over human evolutionary history are necessary to explain the forager population paradox

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1902406116 ◽

2019 ◽

Vol 116 (26) ◽

pp. 12758-12766 ◽

Cited By ~ 9

Author(s):

Michael D. Gurven ◽

Raziel J. Davison

Keyword(s):

Evolutionary History ◽

Homo Sapiens ◽

Vital Rate ◽

Small Scale ◽

Human Populations ◽

Wild Chimpanzee ◽

Population Fluctuations ◽

Vital Rates ◽

Zero Population Growth ◽

Major Adjustment

The rapid growth of contemporary human foragers and steady decline of chimpanzees represent puzzling population paradoxes, as any species must exhibit near-stationary growth over much of their evolutionary history. We evaluate the conditions favoring zero population growth (ZPG) among 10 small-scale subsistence human populations and five wild chimpanzee groups according to four demographic scenarios: altered mean vital rates (i.e., fertility and mortality), vital rate stochasticity, vital rate covariance, and periodic catastrophes. Among most human populations, changing mean fertility or survivorship alone requires unprecedented alterations. Stochastic variance and covariance would similarly require major adjustment to achieve ZPG in most populations. Crashes could maintain ZPG in slow-growing populations but must be frequent and severe in fast-growing populations—more extreme than observed in the ethnographic record. A combination of vital rate alteration with catastrophes is the most realistic solution to the forager population paradox. ZPG in declining chimpanzees is more readily obtainable through reducing mortality and altering covariance. While some human populations may have hovered near ZPG under harsher conditions (e.g., violence or food shortage), modernHomo sapienswere equipped with the potential to rapidly colonize new habitats and likely experienced population fluctuations and local extinctions over evolutionary history.

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The Demography of Two West African (Gambian) Villages, 1951–75

Journal of Biosocial Science ◽

10.1017/s0021932000013390 ◽

1981 ◽

Vol 13 (2) ◽

pp. 219-240 ◽

Cited By ~ 52

Author(s):

W. Z. Billewicz ◽

I. A. McGregor

Keyword(s):

Population Growth ◽

Child Mortality ◽

West African ◽

Small Scale ◽

Wet Season ◽

Birth Rates ◽

Death Rates ◽

Live Births ◽

First Child ◽

Specific Mortality

SummaryFrom a longitudinal study over 25 years (1951–75) of two adjacent Gambian villages, the data allow estimates of population growth, birth rates, age-specific mortality, female fertility, and infertility rates in the two sexes. Such intensive but small scale local inquiries provide valuable information on topics not covered in official published statistics, and also data from which the reliability of some census details can be estimated. There are many similarities but also differences between the two villages. Population growth rate was 1·1% per annum for Keneba and 2·2% for Manduar. Crude death rates averaged 36·7 per thousand for Keneba and 24·7 for Manduar and showed little difference between the sexes. For Keneba and Manduar respectively stillbirth rates were 63·9 and 88·6, first week mortality 49·2 and 44·9 and neonatal mortality 85·2 and 49·6 per thousand live births. In Keneba, where survival to age 5 years averaged 50%, young child mortality was significantly higher than in Manduar but mortality at older ages was not. Season profoundly affected child mortality: about 45% of all deaths under 15 years occurred in the late wet season, August–October. Maternal mortality in Keneba was 10·5 and in Manduar 9·5 per thousand. Crude birth rates averaged 58·4 per thousand for Keneba and 49·0 for Manduar, rates per thousand women aged 15·44 years averaging 248·5 and 215·3 respectively.In both villages mean birth interval increased progressively with the survival of the preceding child. In Keneba the interval increased from about 16 months when the first of the two children was stillborn to nearly 37 months when the first child survived to 2 years. In Manduar the corresponding values were 19 and 36 months. Analyses of obstetric histories indicated that total fertility was of the order of 7·5 live births per woman in Keneba and 6·4 in Manduar. Estimates of primary infertility for females were 3·6% in Keneba and 5·6% in Manduar, and for males 3·1% and 1·9%. Estimates of secondary infertility in females were 13% in Keneba and 19% in Manduar.

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Slow Life History Leaves Endangered Snake Vulnerable to Illegal Poaching

10.21203/rs.3.rs-112390/v1 ◽

2020 ◽

Author(s):

Chris Jolly ◽

Brenton von Takach ◽

Jonathan Webb

Keyword(s):

Life History ◽

Population Growth ◽

Life Histories ◽

Extinction Risk ◽

Adult Mortality ◽

Sensitivity Analyses ◽

Wildlife Trade ◽

Pet Trade ◽

The Impact ◽

Negative Population

Abstract Global wildlife trade is a multibillion-dollar industry and a significant driver of vertebrate extinction risk. Yet, few studies have quantified the impact of wild harvesting for the illicit pet trade on populations. Long-lived species, by virtue of their slow life history characteristics, may be unable to sustain even low levels of harvesting. Here, we assessed the impact of illegal poaching on a metapopulation of endangered broad-headed snakes (Hoplocephalus bungaroides) at gated (protected) and ungated (unprotected) populations. Because broad-headed snakes are long-lived, grow slowly and reproduce infrequently, populations are likely vulnerable to increases in adult mortality. Long-term data revealed that annual survival rates of snakes were significantly lower in the ungated population than the gated population, consistent with the hypothesis of human removal of snakes for the pet trade. Population viability analysis showed that the ungated population has a strongly negative population growth rate and is only prevented from ultimate extinction by dispersal of small numbers of individuals from the gated population. Sensitivity analyses showed that the removal of a small number of adult females was sufficient to impose negative population growth and suggests that threatened species with slow life histories are likely to be especially vulnerable to illegal poaching.

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Slow life history leaves endangered snake vulnerable to illegal collecting

Scientific Reports ◽

10.1038/s41598-021-84745-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Chris J. Jolly ◽

Brenton Von Takach ◽

Jonathan K. Webb

Keyword(s):

Life History ◽

Population Growth ◽

Life Histories ◽

Extinction Risk ◽

Adult Mortality ◽

Sensitivity Analyses ◽

Wildlife Trade ◽

Pet Trade ◽

The Impact ◽

Negative Population

AbstractGlobal wildlife trade is a multibillion-dollar industry and a significant driver of vertebrate extinction risk. Yet, few studies have quantified the impact of wild harvesting for the illicit pet trade on populations. Long-lived species, by virtue of their slow life history characteristics, may be unable to sustain even low levels of collecting. Here, we assessed the impact of illegal collecting on populations of endangered broad-headed snakes (Hoplocephalus bungaroides) at gated (protected) and ungated (unprotected) sites. Because broad-headed snakes are long-lived, grow slowly and reproduce infrequently, populations are likely vulnerable to increases in adult mortality. Long-term data revealed that annual survival rates of snakes were significantly lower in the ungated population than the gated population, consistent with the hypothesis of human removal of snakes for the pet trade. Population viability analysis showed that the ungated population has a strongly negative population growth rate and is only prevented from ultimate extinction by dispersal of small numbers of individuals from the gated population. Sensitivity analyses showed that the removal of a small number of adult females was sufficient to impose negative population growth and suggests that threatened species with slow life histories are likely to be especially vulnerable to illegal collecting.

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Opposite selection pressures on stature and intelligence across human populations

Open Behavioral Genetics ◽

10.26775/obg.2014.05.12 ◽

2014 ◽

Cited By ~ 1

Author(s):

Davide Piffer

Keyword(s):

Human Populations ◽

Selection Pressures

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Accurate age estimation in small-scale societies

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1619583114 ◽

2017 ◽

Vol 114 (31) ◽

pp. 8205-8210 ◽

Cited By ~ 8

Author(s):

Yoan Diekmann ◽

Daniel Smith ◽

Pascale Gerbault ◽

Mark Dyble ◽

Abigail E. Page ◽

...

Keyword(s):

Life History ◽

Bayesian Approach ◽

Age Estimation ◽

Human Life ◽

The Philippines ◽

Monte Carlo Algorithm ◽

Small Scale ◽

Hunter Gatherers ◽

Cultural Life ◽

Ranking Order

Precise estimation of age is essential in evolutionary anthropology, especially to infer population age structures and understand the evolution of human life history diversity. However, in small-scale societies, such as hunter-gatherer populations, time is often not referred to in calendar years, and accurate age estimation remains a challenge. We address this issue by proposing a Bayesian approach that accounts for age uncertainty inherent to fieldwork data. We developed a Gibbs sampling Markov chain Monte Carlo algorithm that produces posterior distributions of ages for each individual, based on a ranking order of individuals from youngest to oldest and age ranges for each individual. We first validate our method on 65 Agta foragers from the Philippines with known ages, and show that our method generates age estimations that are superior to previously published regression-based approaches. We then use data on 587 Agta collected during recent fieldwork to demonstrate how multiple partial age ranks coming from multiple camps of hunter-gatherers can be integrated. Finally, we exemplify how the distributions generated by our method can be used to estimate important demographic parameters in small-scale societies: here, age-specific fertility patterns. Our flexible Bayesian approach will be especially useful to improve cross-cultural life history datasets for small-scale societies for which reliable age records are difficult to acquire.

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The effect of life-history and mode of inheritance on neutral genetic variability

Genetics Research ◽

10.1017/s0016672301004979 ◽

2001 ◽

Vol 77 (2) ◽

pp. 153-166 ◽

Cited By ~ 114

Author(s):

BRIAN CHARLESWORTH

Keyword(s):

Sequence Variation ◽

Adult Mortality ◽

Structured Populations ◽

Human Populations ◽

Effective Population ◽

Transmission Modes ◽

Population Sizes ◽

Age Structured ◽

Infinite Sites Model ◽

Site Diversity

Formulae for the effective population sizes of autosomal, X-linked, Y-linked and maternally transmitted loci in age-structured populations are developed. The approximations used here predict both asymptotic rates of increase in probabilities of identity, and equilibrium levels of neutral nucleotide site diversity under the infinite-sites model. The applications of the results to the interpretation of data on DNA sequence variation in Drosophila, plant, and human populations are discussed. It is concluded that sex differences in demographic parameters such as adult mortality rates generally have small effects on the relative effective population sizes of loci with different modes of inheritance, whereas differences between the sexes in variance in reproductive success can have major effects, either increasing or reducing the effective population size for X-linked loci relative to autosomal or Y-linked loci. These effects need to be accounted for when trying to understand data on patterns of sequence variation for genes with different transmission modes.

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