Human Evolution, Life History Theory, and the End of Biological Reproduction

Cadell Last (M.Sc.)

Evolutionary Anthropologist

Global Brain Institute (GBI)

“Weak fertility and rising life expectancy are driving a unique and relentless aging

structure never seen before.”

- George Magnus (economist)

Overview

• Three major primate life history transitions– Prosimian->Monkey / Monkey -> Apes / Apes -> Humans

• Life History Theory

– Energy budget: Growth, maintenance & reproduction

• Fourth transition emerging? (1750-2050)

• A transition towards a new evolution?

– Biological reproduction -> Cultural reproduction

Transitioning from: “Live Fast, Die Young”

• Primate trend over 60 million years: – From prosimians to humans

– Later sexual maturity / Longer life expectancy

• The Hominoids– Chimpanzees/Bonobos

– Gorillas

– Orangutans

• Increased parental care and social learning with increased brain size

Great Ape and Human Life Histories

Species Sexual Maturity Life Expectancy

Orangutans (Pongo) 9-10 50-55

Gorillas (Gorilla) 8-9 45-50

Chimpanzees (Pan) 8-9 45-50

Human (Homo) 18-20 75-85

“It takes a village to raise a child”

• Life history transition in humans required:

– Parental support by post-reproductive individuals

– Extensive male parental support

• Which led to:

– Menopause

– Concealed ovulation

– Continued non-reproductive sexual activity

Brain Explosion

• Human life history co-evolved with brain expansion (specifically neocortex)

– Life expectancy/brain size correlated in mammals

• Fossil data on:

– Cranium size

– Skeletal ontogeny

– Dental maturation

One Transition; Multiple Waves

Species Time (Mya) Cranial Capacity (cc)

Est. sexual maturity

Est. Life Expectancy

Australopithecines 6-4 450 10 50

Homo habilis 2 600 12-13 60

Homo erectus/ergaster

1.7-0.5 800 15-16 70

Archaic humans 0.3-0.1 1,300 18 80

Life History Theory (LHT)

• Life History Theory: explains “trade-offs” between energy (e) expenditure on biological:

– Growth (g), maintenance (m), reproduction (r)

• Finite energy (e) creates evolutionary strategy between current/future reproduction:

– (e) investment (g)/(m) chances of future (r)

– (e) investment (r) chances of future (r)

LHT in Human Evolution

• All unique human LH patterns emerged as by product of growing neocortex

– i.e., menopause, male-female co-parenting, etc.

• Neocortex increase fuelled w/ cooked meat

– Meat acquired via large-scale hunting w/ technology

• Dependence on cultural & technological processes for energy required increased investment in learning: (e = g/m > r)

Trading Current (R) for Cultural Knowledge

“Childhood became an intellectual and social stage of development requiring increasingly large amounts of time

and energy at the expense of current reproduction.”

Modern Times

• Agricultural age: little-to-no life history change– No extra learning required– No extra energy for 99.9% of people

• Industrial age: demographic transition– Pressures for extra cultural learning emerge– Reduction of fertility (2) and mortality (80)

• Demographic transition– Culturally universal w/ industrialization– Transition likely to be completed globally by 2050– Intensifying further in developed countries

Fertility Rate Declining

• # Countries Below Replacement Level Fertility (<2.1):– According to U.N. (72/195) / CIA World Factbook

(115/224) / World Bank (79/197)

• Many countries at or below 1.5– e.g., South Korea, Japan, Italy, Spain, Germany

• Cyprus (1.61 / 1.45 / 1.47)

• Macau, Singapore, Hong Kong below 1.0

A New Life History Theory Explanation

• Biocultural Life History

– (g)/(m)/(r) is cultural as well as biological

• Investment is cultural learning (g/m) as well as cultural (r) delaying current biological (r)

• Culture starting to model and outcompete biology?

Cultural Evolution Rises

• Parallels between biological and cultural evolution

• Cumulative cultural evolution consumes the human life (g)/(m)/(r)

• All individual and collective economic success dependent on culture

• Life long cultural reproduction as vocation (r)

Fourth Primate Life History Transition?

• Emerging *Early* Trends:

– Permanently delayed biological reproduction

– Increasing life expectancy

• Brain extension: Neocortex to the cloud?

– Outsourcing symbol system to computation

• Tipping point: radical life extension (2050?)

– Cultural reproduction > biological reproduction

– Complexity directed by mind

Stated Clearly…

• A future of increasing biology-technology merger in the human – is a future with significantly reduced biological (r) in favour of cultural (r)

• “Idea sex” as new primary mechanism for evolutionary change

• Transitions:– Prosimian -> Monkey

– Monkey -> Apes

– Apes -> Humans

– Humans -> “Transhumans”

The Human System: A Caveat

• Demographic transition started with Industrial Revolution, but…

– Won’t be completed until industrial transition is complete

• LH is always dependent on energy budgets

– Future of LH dependent on abundant energy

– Fusion (solar/nuclear fusion)

• An abundant energy future enables everyone to participate in cultural reproduction as vocation

“Were individuals able to expend unlimited energy at no cost, in principle they could evolve to grow and develop so rapidly they could begin reproducing

immediately after birth, massively producing offspring, and preserve themselves such that they

never age. In biological reality, however, individuals must live within finite energy “budgets”.”

- Kaplan & Gangestad (2004)

But what about “in cultural reality”?

Thank you for your time!

Now for the idea sex… I mean discussion!