CARTA: Birth to Grandmotherhood: Childrearing in Human Evolution -- Hillard Kaplan: Human Fathers

Summary

In this enlightening lecture, Hillard Kaplan delves into the role of human fathers within the context of human evolution, examining the 'evolved human economy'. By referencing an ecological model, Kaplan discusses the significant family dynamic of kin-based altruism, particularly the downward intergenerational transfers from grandparents to grandchildren. He explains reciprocity and cooperative foraging within foraging societies showcasing the complementary roles of males and females in production and reproduction. Kaplan highlights the unique aspects of human diet and demography compared to chimpanzees, focusing on the importance of caloric intake and surplus as related to lifespan and productivity. While emphasizing the human evolutionary niche's learning-intensive strategies, Kaplan discusses specialized foraging roles of men and women. He concludes by addressing the typical monogamous nature of foraging societies and the ecological variations affecting family economic patterns.

Highlights

• Human fathers contribute significantly to family economies through downward food and resource flows. 🍽️
• Foraging societies rely heavily on kin-based altruism to facilitate family survival and wellbeing. 🏞️
• Specialization between male and female roles evolves from complementary dietary needs and productive capabilities. ⚖️
• The role of human fathers extends beyond direct reproduction to ensuring grandchild support and intergenerational resource flow. 🙌
• Monogamous tendencies in marriages aid in the structured and sustainable family and community economy. 🤝

Key Takeaways

• Human fathers play a critical role in an evolved human economy involving kin-based altruism, reciprocity, and complementarity between sexes. 👨‍👧‍👦
• The dietary habits and foraging skill development in humans contrast significantly with chimpanzees, indicating an evolution in caloric strategies and cooperation. 🍏🍗
• Human lifespan and productivity are tightly intertwined, showcasing the importance of late caloric surplus and long lifespans. ⏳
• Differences in hunting and gathering roles between men and women highlight evolutionary specialization in human societies. 🏹🥥
• Most marriages in foraging societies tend to be monogamous, reflecting broader ecological and social adaptations. 💍

Overview

In this insightful talk by Hillard Kaplan, we take a fascinating journey through the evolutionary role of human fathers within the framework of what is termed the 'evolved human economy'. Kaplan, alongside co-authors and financial supporters, delves deep into the intricate dynamics of families in foraging societies, emphasizing kin-based altruism. He elaborates on how intergenerational resource transfers, from grandparents down to grandchildren, underpin societal structures within these communities.

Kaplan introduces us to the intriguing contrast between human and chimpanzee diets, where humans exhibit specialized foraging and cooperation. He describes the complex economic relations in foraging communities hinging on reciprocity and highlights significant complementarities in male and female roles in reproduction and resource production. Kaplan's insights challenge us to understand the dietary evolution that demands skill-intensive strategies and the compelling caloric dynamics which leverage long human lifespans.

Wrapping up, Kaplan addresses the ecological and cultural intricacies that underlie marital structures and kin interactions in differing societies. His conclusion paints a picture of mostly monogamous unions among foragers, shaped by deeply-rooted cultural norms and cooperative economic models. The variability in production and kin contributions across cultures reveal the nuanced adaptations and evolutionary paths that human societies have trekked through time.

Chapters

• 00:30 - 01:00: Introduction to Human Fathers In this introductory chapter, the theme of 'Human Fathers' is set with a background score. The chapter likely aims to explore the roles, responsibilities, and impacts of fathers in human society, possibly touching upon historical and cultural perspectives. The chapter might also set the stage for more detailed discussions in subsequent chapters.
• 01:00 - 02:00: Evolved Human Economy and Ecological Model This chapter explores the evolving role of human fathers in society, considering the economic and ecological impacts. It delves into how fatherhood is perceived and enacted in modern times, highlighting shifts from traditional roles. It discusses the balance between participation in the workforce and involvement in family life, and how these dynamics are influenced by ecological considerations and economic pressures.
• 02:00 - 03:00: Kin-Based Altruism and Reciprocity The chapter titled 'Kin-Based Altruism and Reciprocity' discusses the evolved human economy through the lens of an ecological model. The speakers, including the author and their collaborators Paul Hooper, John Stiglet, and Mike Gerin, explore this economic model and acknowledge the sponsorship of the National Institute on Aging. The argument proposed in this chapter emphasizes that foraging societies prominently exhibit three principal economic relations. It is also stated that while these relations are a model pattern evident in most groups, not all groups adhere to this pattern.
• 03:00 - 04:00: Complementarity in Specialization This chapter focuses on the three main principles of kin-based altruism, emphasizing the flow of resources from one generation to the next, such as grandparents helping their children and grandchildren. The concept of reciprocity in economic relations plays a crucial role in reducing risk and ensuring stable food resources, highlighting the importance of cooperative behaviors like joint resource production and foraging. In addition, it explores the idea of complementarity in specialization, suggesting that various roles and expertise contribute to the overall effectiveness and success of the group or society.
• 04:00 - 05:00: Dietary Comparisons: Humans vs. Chimpanzees The chapter discusses the dietary habits and comparisons between humans and chimpanzees. It presents a generational diagram intended to illustrate the flow of resources across three generations within families, comparing the grandparental, first, second, and third generations. The diagram, through arrows, highlights the differences and dynamics in resource production and household contributions across these generations to understand dietary patterns comprehensively.
• 05:00 - 06:00: Human Demography and Lifespan In the chapter titled 'Human Demography and Lifespan,' the dynamics of familial relationships and resource distribution are explored. Key concepts include the joint production efforts between husbands and wives, focusing on offspring and the household economy. The chapter also delves into kin altruism, detailing the directional flows of resources, predominantly food, which are depicted as downward and upward flows across generations. Particularly emphasized are the heavier flows downward, indicating that resource distribution is more significant from older to younger generations.
• 06:00 - 08:00: Age-Specific Caloric Production The chapter titled 'Age-Specific Caloric Production' focuses on the evolution of economic relationships centered around reciprocity. It discusses how these relationships are characterized by mutual exchange, such as 'I give you today, you give me tomorrow,' or through sharing the products of labor. The chapter suggests that these economic and social relations evolved as humans began to exploit specialized foraging niches that provided high-quality, calorically dense plant and animal foods. The learning and adaptation required to exploit these niches effectively shaped the structure of human economic interactions.
• 08:00 - 09:00: Specialization in Skill Trajectories The chapter 'Specialization in Skill Trajectories' examines the high degree of specialization in human skill development and production. It highlights a unique pattern where there is an intensive foraging strategy with a late peak in caloric production, suggesting humans specialize deeply into adulthood. The text suggests that cooperation and risk reduction are critical for efficient production. It also emphasizes the complementary roles between male and female inputs in both production and reproduction, reflecting on how human survival strategies are intertwined with social and family structures. The chapter gives insights into these dynamics and makes comparisons with other species' diets and survival strategies to provide a coherent understanding of human dietary evolution.
• 09:00 - 13:00: Food Contributions and Child Care in Foraging Societies The chapter explores the types of consumable resources in foraging societies, using chimpanzees as a comparative model. It lists three categories of foods: collected foods like leaves and fruits, extracted foods such as nuts and tubers, and hunted foods. Both chimpanzees and humans are omnivores, consuming all three food types. The discussion highlights similarities and evolutionary aspects of diet between chimpanzees and humans, emphasizing the insights into human evolution and child care among foraging societies.
• 15:00 - 16:00: Behavioral Menopause in Men The chapter titled 'Behavioral Menopause in Men' discusses the dietary evolution in humans compared to other species, highlighting how humans consume much fewer leaves and fruits in contrast to our ancestors or other animals. Instead, human diets have shifted towards more extracted foods and predominantly hunted items. This shift not only reflects a change in consumption but also a move towards foods that require more skill to acquire, are richer in nutritional value, and come in larger packages. However, these larger package sizes also introduce more variance in dietary intake.
• 16:00 - 18:00: Food Flows in Aging The chapter 'Food Flows in Aging' discusses the interconnectedness of diet and life history, highlighting how human demography differs from that of chimpanzees. It uses a demographic curve to illustrate the concept of remaining years of life as a function of age, starting from birth expectations for foragers.
• 18:00 - 20:00: Conclusion: Human Economy and Reproduction In the concluding chapter titled 'Human Economy and Reproduction,' the author examines the life expectancy of humans compared to chimpanzees, emphasizing differences at the age when reproduction begins and ends. It is highlighted that while chimpanzees generally have an additional 15 years of life post the commencement of reproduction, humans extend this span significantly with an extra 40 years, culminating around 55 years of age. Furthermore, after reaching the age at which reproduction ceases, humans typically live an additional 22 years, indicating significant longevity in human economic development and reproduction cycles compared to their primate relatives.

CARTA: Birth to Grandmotherhood: Childrearing in Human Evolution -- Hillard Kaplan: Human Fathers Transcription

• 00:00 - 00:30 e [Music]
• 00:30 - 01:00 uh so I'm going to be talking about human fathers but I'm going to be doing it in the context of what we're calling
• 01:00 - 01:30 the evolved human econ economy and an ecological model and I'd like to recognize my co-authors in this talk uh Paul Hooper John stiglet and Mike gerin and our funding sponsors the National Institute of on Aging we'll be arguing that there are three principal economic relations en foraging societies and that this is a model pattern meaning that most groups show it but not all groups
• 01:30 - 02:00 so the three principles are kin-based altruism with downward intergenerational transfers that is from grandparents to parents from parents to children and grandparents to grandchildren that reciprocity is another economic relation based upon reducing risk of variance in day-to-day diet and in joint resource production Cooperative foraging and that there's complimentarity in specialization among
• 02:00 - 02:30 the sexes in reproduction household and resource production here's a figure that's meant to diagram three generations of families so this is the grandparental generation this is family one of the first generation family one of the second generation of the third and the different families and these arrows are meant to characterize resource flows
• 02:30 - 03:00 and we are discussing the three types of relationships so between husbands and wives there's joint production of Offspring and the household economy and then there are downward flows with kin altruism so the thicker arrows there's flows in both directions of food going downward and upward and there's also downward flows and upward flows across two generations but always thicker going downward than upward that is more going
• 03:00 - 03:30 downward than going upward and these relationships are meant to characterize reciprocity I give you today you give me tomorrow or we share in the products of our labor I think that this uh economy evolved in relation these relations evolved in in response to specialized foraging Niche that humans eat highquality calorically dense plant and animal Foods that it's a learning
• 03:30 - 04:00 intensive foraging strategy skill intensive that there a late age peak in caloric production and that there's gains to cooperation in production and risk reduction and that there's High complimentarity between the male and female inputs into production and reproduction and so this gives you a feeling of what I'm talking about in terms of the kind of a diet that humans uh eat so this is comparing hum hum to
• 04:00 - 04:30 chimpanzees our closest living relative of three types of resources that you can eat collected foods like leaves and fruits that are just picked off of the the plant extracted gathered fruits plant foods that are like nuts and tubers that require digging or processing to get to and haunted Foods what we can see is that chimpanzees and humans are omnivores they all eat the three types of foods but chimpanzees are
• 04:30 - 05:00 primarily eating leaves and fruits humans eat very almost no leaves and very little fruit much more extracted foods and a much greater hunted proportion of the diet and what we're arguing is is that as you move across these three categories they're getting more difficult to acquire more skill intensive more nutritional value to the foods and bigger package sizes but the big package sizes also create variance
• 05:00 - 05:30 and create needs for sharing so in looking at how this diet links to the rest of the life history we see some striking features of the human demography compared to chimps so this is a curve that looks at the years of life that remain to you as a given a function of your age so if you look at it at age zero it's life expect at Birth foragers
• 05:30 - 06:00 happen to have a life expectancy on average of about 35 years chimpanzees at Birth have about a 13 to 15 year Well what I want you to see here is is that at at the age at which reproduction begins chimpanzees have about 15 more years of life whereas humans have an extra 40 years of life so that would bring them up to 55 and if they make it to the age at which reproduction ceases I average people have an extra 22 years
• 06:00 - 06:30 or of life or so remaining and what you can see here is how particular the human stamp is all the groups are lying on top of one another compared to the chimpanzees and we've even put in Sweden in the 18th century here and they fall right in the middle of the hunter gatherers and the forge or horticulturalist suggesting that this long lifespan is a characteristic feature of our species
• 06:30 - 07:00 and it turns out that if you take the density of deaths and you say for all adults how many deaths occur at this age at this age at this age and we see a peak density of deaths occurring right at about age 70 in the traditional groups it's moved over to the late 80s in modern society but it's it is interesting when we think about a 35e life expectancy that the highest density
• 07:00 - 07:30 of adult deaths is still at age 70 and that's because most of that early death is infancy and so that lowers life expectancy now this is a uh a graph of age specific caloric production and po caloric production so these these two graphs here there there's on my computer they're dashed are the consumption by age so by age 18 you're in the 2,000
• 07:30 - 08:00 calorie range this is males and this is females and these lines are their production this is for the chiman but we've seen very similar curves for the a the hwi the Kung the hza the machenga and Pio what most variable is the female production curve but what you can see is that there's a big caloric deficit in early ages and a caloric Surplus in older ages and if you net them out this is what it looks like in net so you're
• 08:00 - 08:30 getting more expensive as you're growing and then you cross over at around age 20 and then you're a net producer the rest of your life now in terms of looking at the complimentarity between the male and the female inputs in the human case we have a primate commitment to carrying infant and intensive maternal care we heard a lot about that already and there's an incompatibility of care
• 08:30 - 09:00 and hunting because it's very dangerous to be chasing live animals and the protein and fat in game complement carbohydrate Rich plant foods and so what we end up seeing is specialization in alternative skill trajectories of men and women and that what the females give in the way of child care and gathered products complements what the males are giving in the way of hunted protein and fat products
• 09:00 - 09:30 so what we're talking about in terms of the skill intensiveness of the human foraging nich can be seen in in this graph that was done by Rob Walker Kim Hill and myself in which we looked at physical strength plotted on this graph by age and as you could see men are reaching their Peak strength in their early 20s and then this is their hunting return rate that is the amount of calories of meat that they get for every hour they spend and at age 20 they're
• 09:30 - 10:00 poultry 25% as good as they're going to be when they're in middle age what I did was to try to think about this as a contrary to fact experiment a thought experiment I asked well why don't women hunt and why don't men gather well what would they what would happen if women hunted if we make the assumption
• 10:00 - 10:30 that women can't hunt when they are really pregnant and they're lactating a young baby but when they're not really pregnant and they're not lactating they could hunt how much practice would they get and how would how much would they get if they compare that to to Gathering so this is the this is taking the A and doing the this is the real for women and this is the hypothetical if they h hunted this is the real for men
• 10:30 - 11:00 and this is the hypothetical for Gathering and this is the cumulative calories net after consuming all of their own caloric needs that they would produce over life because the a women are spending so much of their time in child care they're actually not producing enough to feed themselves so they're becoming increasingly costly uh calorically as they age but less so by gathering and ironically for the men it goes the other
• 11:00 - 11:30 direction and this is because when you do learn how to hunt and after a while you can get very good at it so when we sum all of this up and we look at the percent food contributions so this is taking the 10 societies for which we can quantify the daily caloric production of individuals and uh in 2001 we calculated that on average and
• 11:30 - 12:00 there's quite a bit of variability across foraging societies men are acquiring about 2/3 of of the calories and most of the protein but when you sum out what the women are eating for themselves almost all of the food energy extra food energy is being produced by the men now as I pointed out in the bottom of that other figure is that women are
• 12:00 - 12:30 spending a huge amount of time in child care and here is data from the chimane in which we looking at who's who are the different caretakers of the kids and moms are doing the the bulk of the caretaking in the tumman I think this is pretty cross-culturally variable how much other Alo parents help but there's no question that it's Mom who's doing the bulk of it
• 12:30 - 13:00 and then when you add the fact that women are helping with the food processing they're the men and the women are each contributing different NE necessary components of the reproductive and the productive economy and as a result it looks like uh polygyny is relatively uncommon in foraging societies that in almost 50% of the society's less than 5% of marriages are
• 13:00 - 13:30 poist but if you sum this all up most of the marriages in Hunter gather societies are monogamous now this is a figure that we've put together that takes regression models and looks at who who shared with Who as a function of uh their their age and their relationship to one another so this this actually measures in the
• 13:30 - 14:00 tumman the food flows going up and going down as you can see they're going in both directions this side Nets it all out so that you can see it more clearly and what I want you to get out of this figure is is that almost all of the net arrows are going downward across the generations and the one exception is one Arrow going from adult men to to their
• 14:00 - 14:30 uh in-laws but that then is being got brought down to the In-laws kids and so in in on net it's still a downward process and we're seeing the flows going from men to women men to women uh in in the same generation and this is not to say that men are more productive than women it's to say that they are helping women do the other tasks in life by providing the
• 14:30 - 15:00 net calories now another thing that we found is that while it's true that men can continue to reproduce into old age most men don't in fact most men have effective behavioral menopause because they when their wife goes
• 15:00 - 15:30 through menopause they don't have any more kids this is for the tumane so 90% of men did not reproduce again after their wife went through menopause some those who did were polygynously married there were a few who did it for other reasons as well and we found a very similar pattern for a forages where about 80 some on% didn't reproduce again after their wife
• 15:30 - 16:00 went through menopause now this graph looks at for the tumman the flows from Mom to children from dad to children from Grandma to grandchildren from Grandpa to grandchildren and from husband to wife and the biggest flows as we saw from the other figure are from Father which is peeking out at around 3,00 th000 calories to his children per day
• 16:00 - 16:30 and it's dropping as they're getting older and and then he starts to pick up and starts to give to grandchildren the dotted blue line and has a peak in in the 60s and then drops down again here is the women with the same similar age Peak just lower and a similar age Peak for the grandchildren in the food transfers what you can see here is that at about age
• 16:30 - 17:00 70 is when people no longer have net transfers downward this is when they're reaching the age at which they can just basically produce what they can consume through aging and here's a way of looking at how these two things may be linked together so here are the expected number of descendants based upon a normal family growth pattern uh for hunter gatherers
• 17:00 - 17:30 that you'd have a your Peak number of dependent kids in your 30s and then your Peak number of dependent grandchildren are going to be in your 60s and what we're seeing here is is that it's just as this is going down we're really seeing the this is the mortality curve the risk of instantaneous risk of mortality and it's stays really quite low until about age
• 17:30 - 18:00 60 and that's where we see the really big acceleration so to conclude I would say that uh humans have a unique species typical economy that's based on an ecological niche characterized by a learning intensive food acquisition strategy uh a life history strategy of high parental investment High rates of juvenile and adult survival and long lifespan and that the economy is
• 18:00 - 18:30 organized by three principles kin-based altruism in downward intergenerational transfers reciprocity and Cooperative production among unrelated individuals and complimentarity and specialization by sex and Joint production and re reproduction and that men as fathers and grandfathers acquire energy to support wives children and grandchildren while women engage in a mix of energy
• 18:30 - 19:00 production processing and child care and that most marriages are monogamous among foragers and it appears as if most men cease to reproduce when their wives reach menopause and lastly I've been talking in very broad Strokes here generalizing among foraging groups based upon data but there's a great deal of variation especially when look at the full breadth
• 19:00 - 19:30 of the ethnographic literature and I would offer the suggestion that variations away from this modal pattern are going to be due to differences in age profiles of production so when children are more productive there'll be less downward flows there going to be factors that would affect how much men can really make a difference to women uh and their children and that's going to cause ecological variation and again the the gains from cooperation are going to
• 19:30 - 20:00 vary from place to place [Music]