Slow Life History Research Articles

Chameleon biogeographic dispersal is associated with extreme life history strategies

Understanding the role of traits in dispersal is necessary to improve our knowledge of historical biogeography, community assembly processes and predictions of species' future movements. Here we aimed to determine the relationship between three traits (coastal distribution, body size, position on the fast/slow life history continuum) and past dispersal probability on an evolutionary timescale in chameleons (Chamaeleonidae). Using species' distribution data we identified the nine most important biogeographic regions for all included chameleons (181/217 species). We compiled life history trait data and used phylogenetic factor analysis to infer independent body size and fast/slow life history trait axes. Finally, we tested whether traits and trait combinations related to biogeographic dispersal success in the past, using trait‐dependent biogeographic models. All three traits were associated with past biogeographical movements. Lineages having coastal distributions and those with large bodies had higher dispersal probabilities. Interestingly, chameleons with either a very fast or very slow life history were more successful dispersers than species with an intermediate strategy. Together, the three traits – coastal, large‐bodied and extreme life history – form a dispersal syndrome. Traits have played an important role in the biogeographic history of chameleons. While only fast traits have been linked to present‐day invasion success in reptiles, both extremes of the life history spectrum were likely advantageous for dispersal and establishment during past biogeographic movements. Fast‐living species may be less susceptible to stochastic extinction in the first phases of a colonization (due to rapid population growth), and slow‐living species may be less vulnerable to environmental stochasticity (due to low demographic variability). Our results call for broader analyses testing the general influence of life history strategy in biogeographic dispersal success, which would help explain species distribution patterns on Earth.

Global warming leads to larger bats with a faster life history pace in the long-lived Bechstein’s bat (Myotis bechsteinii)

Whether species can cope with environmental change depends considerably on their life history. Bats have long lifespans and low reproductive rates which make them vulnerable to environmental changes. Global warming causes Bechstein’s bats (Myotis bechsteinii) to produce larger females that face a higher mortality risk. Here, we test whether these larger females are able to offset their elevated mortality risk by adopting a faster life history. We analysed an individual-based 25-year dataset from 331 RFID-tagged wild bats and combine genetic pedigrees with data on survival, reproduction and body size. We find that size-dependent fecundity and age at first reproduction drive the observed increase in mortality. Because larger females have an earlier onset of reproduction and shorter generation times, lifetime reproductive success remains remarkably stable across individuals with different body sizes. Our study demonstrates a rapid shift to a faster pace of life in a mammal with a slow life history.

Extinction risk, reconstructed catches and management of chondrichthyan fishes in the Western Central Atlantic Ocean

AbstractChondrichthyan fishes are among the most threatened vertebrates on the planet because many species have slow life histories that are outpaced by intense fishing. The Western Central Atlantic Ocean, which includes the Greater Caribbean, is a hotspot of chondrichthyan biodiversity and abundance, but has been characterized by extensive shark and ray fisheries and a lack of sufficient data for effective management and conservation. To inform future research and management decisions, we analysed patterns in chondrichthyan extinction risk, reconstructed catches and management engagement in this region. We summarized the extinction risk of 180 sharks, rays and chimaeras, including 66 endemic and 14 near‐endemic species, using contemporary IUCN Red List assessments. Over one‐third (35.6%) were assessed as Vulnerable, Endangered or Critically Endangered, primarily due to overfishing. Reconstructed catches from 1950 to 2016 peaked in 1992, then declined by 40.2% thereafter. The United States, Venezuela and Mexico were responsible for most catches in the region and hosted the largest proportions of the regional distributions of threatened species, largely due to having extensive coastal habitats in their Exclusive Economic Zones. The quantity and taxonomic resolution of fisheries landings data were poor in much of the region, and national‐level regulations varied widely across jurisdictions. Deepwater fisheries represent an emerging threat, although many deepwater chondrichthyans currently have refuge beyond the depths of most fisheries. Regional collaboration as well as effective and enforceable management informed by more complete fisheries data, particularly from small‐scale fisheries, are required to protect and recover threatened species and ensure sustainable fisheries.

Too Many Males or Too Many Females? Classroom Sex Ratio, Life History Strategies and Risk-Taking Behaviors

Prior research finds that sex ratio, defined as the proportion of males and females in a given context, is related to engagement in risk-taking behaviors. However, most research operationalizes sex ratio at a local context (e.g., regional or county), which fails to reflect with precision the sex ratios contexts of individuals at a closer level. Furthermore, the relationship between sex ratio and risk-taking behaviors may be affected by individuals’ life history strategy, with previous studies showing fast life history strategies linked to risk-taking behaviors, compared to slow life history strategies. The present study analyzes the relationship between classroom sex ratio and risk-taking behaviors and the interaction between classroom sex ratio and life history strategy in adolescents. The sample comprised 1214 participants nested in 57 classrooms, 49.75% females, 91.5% Spanish and a mean age of 16.15 years (SD = 1.23, range 14–21). Results from multilevel modeling showed a negative relation between classroom sex ratio and risk-taking behaviors in female adolescents with faster life history strategy. By contrast, classroom sex ratio in male adolescents related positively to risk-taking behaviors but did not interact with life history strategy. These findings underscore the importance of studying proximate sex ratio on risk-taking behaviors in adolescents and underline its potential influence in the development and expression of life history strategies.

Effectiveness of long‐distance translocation of eastern diamondback rattlesnakes

AbstractWildlife translocations have the potential to assist conservation efforts by mitigating mortality caused by site‐specific human activities. Despite the potential, the effectiveness of snake translocations for conservation purposes is not yet clear. Eastern diamondback rattlesnakes (Crotalus adamanteus, EDB) have limited ability to adapt to habitat loss and fragmentation due to the species' slow life history, high habitat specificity, and minimal dispersal ability. We translocated a cohort of EDBs to investigate the potential of using translocations as a conservation tool for this species. In July 2018, we translocated 12 adult eastern diamondback rattlesnakes from Parris Island Marine Corps Recruit Depot to an inland wildlife management area. We used radio‐telemetry data to examine the effects of translocation on home‐range size and average daily movement. We used known‐fate survival models to examine adult survival post‐translocation. Post‐translocation home ranges were larger than the pre‐translocation home ranges and EDBs moved more, on average, per day post‐translocation. We failed to detect an effect of translocation on 2‐year survival probability. We suspect that large post‐translocation home ranges and average daily movements reflected the need to find suitable ambush and hibernacula sites and differences between coastal and inland habitats. More research is needed to determine the long‐term viability of translocated rattlesnake populations. Our results suggest that translocations may be a viable conservation and mitigation strategy for eastern diamondback rattlesnakes.

Effects of childhood adversity on smartphone addiction: The multiple mediation of life history strategies and smartphone use motivations

Given its negative consequence, the high prevalence of smartphone addiction has become a matter for public concern in recent years. This study takes an evolutionary approach to understanding individual differences in one's vulnerability to smartphone addiction and investigate the role childhood adversity and life history (LH) strategies may play in smartphone addiction via various smartphone use motivations. We recruited 956 Chinese university students between the ages of 16 and 28 (M = 19.35, SD = 1.07) who voluntarily completed an anonymous online questionnaire. Results of path analysis showed a significant direct effect of childhood adversity on smartphone addiction. Moreover, childhood adversity was negatively associated with slow LH strategy, which was negatively correlated with smartphone addiction in the path model. Both pastime and social conformity were significant motivation factors, but they had opposite mediating effects on the relationship between slow LH strategy and smartphone addiction. Our findings improved the knowledge of the complex motivational processes between childhood adversity and smartphone addiction from LH perspective. The findings suggest that people with childhood adversity are at-risk for smartphone addiction, but the opposite mediating effects of two motivation factors illustrate the complex influence LH strategies have on human behavior. Various internal mechanisms should be considered simultaneously in future research to develop a more comprehensive understanding of and effective interventions for smartphone addiction.

Effects of unregulated international fishing on recovery potential of the sandbar shark within the southeastern United States

Coastal sharks are challenging to manage in the United States due to their slow life history, limited data availability, history of overexploitation, and competing stakeholder interests. Furthermore, species like the sandbar shark ( Carcharhinus plumbeus) are subjected to international exploitation unmanaged by the US. We conducted a management strategy evaluation using Stock Synthesis on the sandbar shark to test the performance of various configurations of a threshold harvest control rule. In addition to uncertainties addressed in the operating model (OM), we built multiple implementation models to address uncertainties related to future levels of a partially unmanaged source of removals, the combined Mexican and US recreational (MexRec) fleet. We found that the presence of unregulated removals had the potential to significantly influence the success of the various management procedures (MPs) tested. Notably, if MexRec catches continue to increase with total stock abundance following historical trends, the rate of MexRec removals will be too large to allow the sandbar shark to recover across OMs. We present trade-offs between performance metrics across a range of 24 MPs and three implementation models.

The Mediating Role of Chinese College Students' Control Strategies: Belief in a Just World and Life History Strategy.

The harshness and unpredictability of early life circumstances shape life history strategies for trade-offs between the resources devoted to somatic and reproductive efforts of individuals in the developmental process. This paper uses belief in a just world as a reflection of early environmental cues to predict an individual’s life history strategies. Research has found that belief in a just world influences life history strategies through a sense of control. However, the relationship between a sense of control and a life history strategy is flawed because influencing life history strategies should be intrinsic to control strategies rather than a sense of control. A total of 408 Chinese undergraduate students completed the Personal Belief in a Just World Scale, Mini-K Scale, and Primary and Secondary Control Scale. Structural equation modeling suggested that belief in a just world can directly or indirectly influence life history strategies through primary and secondary control strategies, respectively; there was no statistical difference in the degree of influence between the two paths. These results deepen our understanding of the underlying mechanisms in the relationship between belief in a just world and life history strategies, which can be utilized to ensure a slow life history strategy among Chinese university students in the future.

Life History Strategies, Prestige, and Dominance: An Evolutionary Developmental View of Social Hierarchy.

Although evidence documents the use of prestige and dominance for navigating group hierarchies, little is known about factors that explain people's orientation toward prestige versus dominance. The current research applied a life history perspective to assess the role life history strategies play in prestige and dominance. Four studies document associations between adopting a slow life history strategy and having an orientation toward prestige. We also saw some (less consistent) evidence that people's orientation toward prestige is rooted in exposure to predictable childhood environments, a known antecedent of slow life history strategies. Although we observed some evidence that exposure to unpredictable childhood environments was associated with dominance, there was little direct evidence that this relationship was explained by a fast life history strategy. Findings suggest that an orientation toward prestige is likely to be observed in people with a slow life history, who adopt a long-term time horizon for planning and decision-making.

Early Development Drives Variation in Amphibian Vulnerability to Global Change

Understanding how natural selection determines species’ life histories can reveal their resilience or sensitivity to anthropogenic changes. For example, the safe harbor hypothesis posits that natural selection will favor life histories that maximize the time spent in the safest life stages; a second theoretical prediction suggests that species with complex life histories will maximize the growth potential of a life stage relative to its safety. Amphibians exhibit complex life histories, with a diversity of developmental strategies occurring across taxa. Many strategies involve the complete elimination of a particular life stage, and thus provide an excellent opportunity to evaluate the main tenets of the safe harbor hypothesis and understand the consequences of this developmental variation for conservation of threatened amphibians. We develop a general framework for understanding developmental life histories of amphibians – including the special cases of paedomorphism, direct development, and viviparity – based on the relative growth potential and safety offered by aquatic and terrestrial habitat, which we tested using a global trait database. We then compare the IUCN Red List status of species differing in developmental mode, revealing that most fully aquatic species and species with an aquatic larval stage are currently of Least Concern, despite the fact that freshwater habitats are being lost at a much faster rate compared with terrestrial ecosystems. The higher proportion of direct developing and viviparous species that are threatened can be attributed to their smaller ranges, the fact that they are more likely to be found in rainforest habitats, and their relatively slow life histories. We conclude that an amphibian’s developmental mode reflects the relative costs and benefits of different habitats, and that this could contribute to the resilience or vulnerability of amphibians to future anthropogenic change.

Short-lived species move uphill faster under climate change

Climate change is pushing species ranges and abundances towards the poles and mountain tops. Although many studies have documented local altitudinal shifts, knowledge of general patterns at a large spatial scale, such as a whole mountain range, is scarce. From a conservation perspective, studying altitudinal shifts in wildlife is relevant because mountain regions often represent biodiversity hotspots and are among the most vulnerable ecosystems. Here, we examine whether altitudinal shifts in birds’ abundances have occurred in the Scandinavian mountains over 13 years, and assess whether such shifts are related to species’ traits. Using abundance data, we show a clear pattern of uphill shift in the mean altitude of bird abundance across the Scandinavian mountains, with an average speed of 0.9 m per year. Out of 76 species, 7 shifted significantly their abundance uphill. Altitudinal shift was strongly related to species’ longevity: short-lived species showed more pronounced uphill shifts in abundance than long-lived species. The observed abundance shifts suggest that uphill shifts are not only driven by a small number of individuals at the range boundaries, but the overall bird abundances are on the move. Overall, the results underscore the wide-ranging impact of climate change and the potential vulnerability of species with slow life histories, as they appear less able to timely respond to rapidly changing climatic conditions.

Towards positive organization. The evolution of gratitude

Purpose: Establishing the way the life history (LH) strategies and gratitude are related to each other. Design/methodology/approach: Life History Theory provides an evolutionary framework for understanding specific developmental paths of species and individuals. There are certain trade- offs during a lifespan of an individual, they must face (for instance, somatic or reproductive effort, quality or quantity of offspring, mating or parenting). Depending on the choices a person makes, they exhibit a slow or a fast life history (LH) strategy. A latent variable underlying a set of solutions (strategy) is called K-Factor and is used to measure individual differences with regard to the pace of one’s LH. People with a slow LH exhibit greater prosociality, tend to form long-term sexual relationships and their sexual maturation is slowed down. On the other hand, gratitude facilitates prosociality and altruism, builds social resources and acts as a moral barometer. In recent years we observe an increasing attention to the issue of gratitude both in academic publications and popular press in various fields including economics, management and organizational sciences. All these disciplines draw from relatively new and contemporarily flourishing field of psychology – positive psychology. We deployed the Gratitude Questionnaire (GQ-6) for the measurement of gratitude and the Mini-K Short Form for the measurement of LH strategies. 197 students took part in the study (138 females, 59 males). Findings: A positive correlation between slow LH strategy and gratitude was found in women. Originality/value: Investigations on the relationship between gratitude and LH strategies show a fragment of the landscape of human personality. Slow LH people seem to be more grateful and thus display more prosocial traits while restraining selfishness which can lead to achieving the delayed social benefits. On the other hand, low-K individuals in organizational context have smaller willingness/ability to reciprocate to their benefactors and to build social bonds. Such individuals presenting exploitative interpersonal style should be detected at the beginning of a selection process by HR specialists. Keywords: life history theory, life history strategies, gratitude, positive psychology, positive psychology interventions in organizations. Category of the paper: research paper.

How do reproduction, parenting, and health cluster together? Exploring diverging destinies, life histories and weathering in two UK cohort studies.

Life history theory researchers often assume reproductive, parenting and health behaviours pattern across a fast-slow continuum, with 'fast' life histories (typified by short lifespans, early maturation and investing in quantity over quality of children) favoured in poor quality environments and/or when resources are scarce. Some researchers further reduce this down to a simplistic 'fast' versus 'slow' dichotomy. Some of these ideas, with different theoretical motivations, are echoed in the 'diverging destinies' and 'weathering' frameworks developed in the social sciences. Whether clustering of reproductive, parenting and health traits exists has rarely been empirically tested, however. Using latent class analysis on data on mothers from the UK's Millennium Cohort (MCS) and Born in Bradford (BiB) studies, we explored whether reproduction and parenting traits clustered into 'diverging destinies', whether 'weathering' effects tied together health and reproduction, and whether all three domains were combined into either 'fast' vs 'slow' life histories, or into three groups more indicative of a fast-slow continuum. We leveraged ethnic diversity in these samples to examine four groups of mothers separately: 1. MCS White British/Irish (n = 15,423); 2. MCS Pakistani-origin (n = 923); 3. BiB White British (n = 3937); 4. BiB Pakistani-origin (n = 4351), and explored whether faster 'weathering' was evident amongst Pakistani-origin mothers. Both two and three class models emerged as potential descriptions of latent subgroups, potentially providing support for fast and slow life histories or a continuum of traits. However, response profiles provided only limited support for theoretical predictions of which traits should cluster together, with inconsistent and restricted clustering of traits both within and between the domains of reproduction, parenting, and health. In addition, trait clustering was more pronounced amongst White mothers and we found no clear evidence supporting faster 'weathering' amongst Pakistani-origin mothers; the observed clustering instead suggested that cultural constraints may influence linkages between traits. Our results therefore provide some limited support for models which suggest certain traits cluster together in predictable ways, but it is also clear that theoretical frameworks should not emphasise very rigid clustering of large numbers of traits and should allow for contextual influences on clustering.

Palaeohistology reveals a slow pace of life for the dwarfed Sicilian elephant

The 1-m-tall dwarf elephant Palaeoloxodon falconeri from the Pleistocene of Sicily (Italy) is an extreme example of insular dwarfism and epitomizes the Island Rule. Based on scaling of life-history (LH) traits with body mass, P. falconeri is widely considered to be ‘r-selected’ by truncation of the growth period, associated with an early onset of reproduction and an abbreviated lifespan. These conjectures are, however, at odds with predictions from LH models for adaptive shifts in body size on islands. To settle the LH strategy of P. falconeri, we used bone, molar, and tusk histology to infer growth rates, age at first reproduction, and longevity. Our results from all approaches are congruent and provide evidence that the insular dwarf elephant grew at very slow rates over an extended period; attained maturity at the age of 15 years; and had a minimum lifespan of 68 years. This surpasses not only the values predicted from body mass but even those of both its giant sister taxon (P. antiquus) and its large mainland cousin (L. africana). The suite of LH traits of P. falconeri is consistent with the LH data hitherto inferred for other dwarfed insular mammals. P. falconeri, thus, not only epitomizes the Island Rule but it can also be viewed as a paradigm of evolutionary change towards a slow LH that accompanies the process of dwarfing in insular mammals.

Do Early Life Experiences Predict Variation in the General Factor of Personality (GFP)?

ObjectiveThe controversial General Factor of Personality (GFP) has been proposed as an indicator of social effectiveness and a slower life history strategy. An alternative hypothesis holds that only meta-trait alpha, comprising agreeableness, conscientiousness, and emotional stability, is a slow life history indicator. This study tested whether the GFP and/or alpha emerges from both self- and stranger-ratings, and whether either is predicted by indicators of harsh childhood ecologies.MethodsU.S. undergraduate participants (N = 366) completed a Big Five instrument, a measure of socially desirable response bias, and brief (thin slice) videotaped interviews. Raters scored the interviews using the same Big Five instrument.ResultsStructural equation modeling of the self-report data yielded a well-fitting GFP, which was positively associated with father closeness. Meta-trait alpha, based on self-report, was associated with both father closeness and neighborhood stress, but showed positive loadings only for agreeableness and emotional stability. Stranger-rating data failed to yield either a well-fitting GFP or metatrait alpha.ConclusionsOur findings are equivocal regarding the usefulness of the GFP specifically, and higher-order personality factors generally, in evolutionary personality science.

TU69. SCHIZOPHRENIA GENETIC LIABILITY AND CLOZAPINE DOSES: A FIRST STEP TOWARDS THE POLYGENIC ANALYSIS OF RESPONSE TO ANTIPSYCHOTIC TREATMENT

SD–IE is a strategic differentiation effect present amongst indices of life history (LH), such that persons and populations of slow LH are more differentiated compared to those of fast LH. We found that this phenomenon is present amongst provinces in Italy and Spain, similarly to demonstrations among US states and Japanese prefectures. The average effect size of SD–IE was found to be bigger in Spain and Italy. We also tested cognitive differentiation as a function of life history speed and IQ (high-K and high-IQ provinces having higher cognitive differentiation), and found that these effects are also present in the Italian and Spanish regions. Most cognitive differentiation effects were statistically significant in spite of the small number of provinces, but all trended in the predicted direction. We discuss the findings from a bio-historical perspective, taking into account the ethnic variability present in Spain and Italy.

Maternal stress effects on infant development in wild Verreaux's sifaka (Propithecus verreauxi)

Maternal effects mediated by nutrients or specific endocrine states of the mother can affect infant development. Specifically, pre- and postnatal maternal stress associated with elevated glucocorticoid (GC) output is known to influence the phenotype of the offspring, including their physical and behavioral development. These developmental processes, however, remain relatively poorly studied in wild vertebrates, including primates with their relatively slow life histories. Here, we investigated the effects of maternal stress, assessed by fecal glucocorticoid output, on infant development in wild Verreaux’s sifakas (Propithecus verreauxi), a group-living Malagasy primate. In a first step, we investigated factors predicting maternal fecal glucocorticoid metabolite (fGCM) concentrations, how they impact infants’ physical and behavioral development during the first 6 months of postnatal life as well as early survival during the first 1.5 years of postnatal life. We collected fecal samples of mothers for hormone assays and behavioral data of 12 infants from two birth cohorts, for which we also assessed growth rates. Maternal fGCM concentrations were higher during the late prenatal but lower during the postnatal period compared to the early/mid prenatal period and were higher during periods of low rainfall. Infants of mothers with higher prenatal fGCM concentrations exhibited faster growth rates and were more explorative in terms of independent foraging and play. Infants of mothers with high pre- and postnatal fGCM concentrations were carried less and spent more time in nipple contact. Time mothers spent carrying infants predicted infant survival: infants that were more carried had lower survival, suggesting that they were likely in poorer condition and had to be cared for longer. Thus, the physical and behavioral development of these young primates were impacted by variation in maternal fGCM concentrations during the first 6 months of their lives, presumably as an adaptive response to living in a highly seasonal, but unpredictable environment.Significance statementThe early development of infants can be impacted by variation in maternal condition. These maternal effects can be mediated by maternal stress (glucocorticoid hormones) and are known to have downstream consequences for behavior, physiology, survival, and reproductive success well into adulthood. However, the direction of the effects of maternal physiological GC output on offspring development is highly variable, even within the same species. We contribute comparative data on maternal stress effects on infant development in a Critically Endangered primate from Madagascar. We describe variation in maternal glucocorticoid output as a function of ecological and reproductive factors and show that patterns of infant growth, behavioral development, and early survival are predicted by maternal glucocorticoids. Our study demonstrates how mothers can influence offspring fitness in response to challenging environmental conditions.

Slow Life History Strategies and Increases in Externalizing and Internalizing Problems During the COVID-19 Pandemic.

The COVID‐19 pandemic is but one of many instances of environmental adversities that have recurred in human history. Biobehavioral resource allocation strategies, known as fast (reproduction‐focused) versus slow (development‐focused) life history (LH) tradeoff strategies, evolved to deal with environmental challenges such as infectious diseases. Based on 141 young people and their mothers observed prior to (ages 9 and 13) and during (age 20) COVID‐19, we investigated longitudinal relations involving slow LH strategies. The results support the adaptive role of slow LH strategies in reducing COVID‐related increases in externalizing problems. In addition, the effect of early adversity on COVID‐related increases in externalizing was mediated, and the effect on COVID‐related increases in internalizing was moderated, by slow LH strategies.

Ethnic Culture as Related to Sexual and Reproductive Behavior in the Republic of Suriname: The Pervasiveness of Culture

We examined the effects of culture and ethnicity on life history strategies in terms of sexual and reproductive behaviors. The sample included 500 adults, aged 25–50 years, from the five major ethnic groups in Suriname, i.e., the Maroons, Creoles, Hindustani, Javanese, and Mixed. First, there were strong gender differences: men reported to have had more sex partners and to have had their first sexual experience earlier than women, whereas women had their first child earlier and had more children than men. Second, in general, ethnicity affected life history substantially. The Maroons stood out by a relatively fast life history: they reported to have had more sexual partners, to have had their first sex and first child at an earlier age, and to have more children than all other groups. The Creoles were in general similar to the Maroons, whereas the Hindustani and the Javanese were characterized by a relatively slow life history: they reported to have had the lowest number of sexual partners, to have had their first sex and first child at the latest age, and to have had the lowest number of children. The differences between the ethnic groups were upheld when controlling for income, educational level, and father absence during childhood. A lower education was associated with reporting to have had one’s first sex as well as one’s first child at a younger age and children who grew up without a father reported to have had their first sex at a younger age.

Macronutrient composition of olive baboon (Papio anubis) milk: A comparison to rhesus macaque (Macaca mulatta) milk.

This study was designed to (1) characterize the macronutrient composition of olive baboon (Papio anubis) milk, (2) compare baboon milk composition to that of rhesus macaques (Macaca mulatta), and (3) evaluate the association between the proportion of milk energy derived from protein and relative growth rate within anthropoid primates. A single milk sample was collected from each of eight lactating olive baboons ranging between 47- and 129-days postparturition and six rhesus macaques from 15- to 92-days living at the same institution under identical management conditions. Macronutrient composition (water, fat, protein sugar, and ash) was determined using standard techniques developed at the Nutrition Laboratory at the Smithsonian National Zoological Park. Baboon milk on average contained 86.0% ± 0.6% water, 4.7% ± 0.5% fat, 1.6% ± 0.04% protein, 7.3% ± 0.07% sugar, and 0.165% ± 0.007% ash. Baboon milk gross energy (GE) averaged 0.81 ± 0.04 kcal/g with 51.9% ± 2.6% from fat, 11.8% ± 0.7% from protein, and 36.2% ± 2.0% from sugar. Baboon milk demonstrated strong similarity to milk composition of the closely phylogenetically related rhesus macaque (86.1% ± 0.3% water, 4.1% ± 0.4% fat, 1.69% ± 0.05% protein, 7.71% ± 0.08% sugar, 0.19% ± 0.01% ash, and 0.78 kcal/g). There was no statistical difference between baboon and macaque milk in the proportions of energy from fat, sugar, and protein. Baboon milk can be described as a high sugar, moderate fat, and low protein milk with moderate energy density, which is consistent with their lactation strategy characterized by frequent, on-demand nursing and relatively slow life history compared to nonprimate mammal taxa. The milk energy from protein of both baboon and macaque (12.8% ± 0.3%) milk was intermediate between the protein milk energy of platyrrhine (19.3%-23.2%) and hominoid (8.9%-12.6%) primates, consistent with their relative growth rates also being intermediate. Compared to these cercopithecid monkeys, platyrrhine primates have both higher relative growth rates and higher milk energy from protein, while apes tend to be lower in both.