Walking Upright The cost of human evolution

LENScience Senior Biology Seminar Series 2010 Walking Upright The cost of human evolution Peter Gluckman, Alan Beedle, Tatjana Buklijas, Jacquie Bay 14 th October 2010

Human Evolution

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Walking Upright Natural Selection - pre-existing variation - environmental conditions Speciation Adaptive Radiation

New Zealand Scholarship To use biological knowledge and thinking skills to analyse the biological situation presented and integrate ideas into a coherent response

NCEA Level 3 AS: 3.1 Ecological Niche 3.2 Contemporary Biological Issue 3.3 DNA and Gene Expression 3.4 Animal Behaviour & Plant Responses 3.5 Processes & Patterns of Evolution 3.6 Applications of biotechnological techniques 3.7 Trends in Human Evolution

Human Evolution Bipedalism The Brain Cultural Evolution Life History Evolution and Medicine

Hominin Evolution Homo erectus Sahelanthropus tchadensis? Ardipithecus ramidus A.anamensis A.afarensis? Kenyanthropus platyops Australopithecus africanus? A.garhi H. habilis H.rudolfensis H. ergaster Homo heidelbergensis Homo floresiensis Homo sapiens Homo neanderthalensis? Orrorin tungenensis A. bahrelghazali Paranthropus robustus P.aethiopicus Paranthropus boisei Present 7 6 5 4 3 2 1 0 Time (Millions of Years Ago)

Peter s 1 st section...

An essential feature of humans

The Importance of Bipedalism Essential human feature. Charles Darwin, Descent of Man: Bipedalism freed the hands and arms from the use for locomotion and support, for finer tasks (work with tools, fight with weapons). More efficient locomotion.

Bipedalism: Australopithecus afarensis 4-3 MYA Lucy 3MYA Habitually Bipedal Adapted for bipedal walking Not efficient for running

Homo Species 2MYA Obligatory bipedalism Larger body size Meat becomes key part of diet Cooking and tools Longer prepubertal period Larger brain size, deviates from other hominoids

Anatomy of Bipedalism

Problems with Bipedalism Vulnerability of Neck Hernias Flat Feet Varicose Veins Distorted Foot Bones Back Pain Birthing Difficulties Time Taken Learning to Walk Maternal dependency

Environmental Change and Bipedalism Continuous Forest Change in availability of food Wider range needed to get food Wooded Savannah

Replacing knucklewalking with a more efficient form of locomotion?

Net cost of transport for chimpanzee quadrupedal walking, chimpanzee bipedal walking and human walking Sockol M. D. et.al. PNAS 2007;104:12265-12269 2007 by National Academy of Sciences

Published by AAAS Ardipithecus ramidis

Ardipithecus ramidis A. Gibbons Science 326, 36-40 (2009) Published by AAAS

Alternative Explanations Thermoregulation Predator avoidance Carrying capacity Reproductive strategies

Brain Development followed bipedalism Log Brain Volume (cm 3 ) A.boisei A.afarensis H. sapiens H. erectus H. habilis Gorilla Chimp Orang-utan Hominins Australopithecines Great Apes Log body weight (kg) Redrawn from Bonner J.T., Why Size Matters. Princeton University Press 2006

Advantages Arising from Brain Development Social Structure Communication of Abstract Thought Communication / Language Technology Art / Religion / Music / Science Culture / Learning

Relationship between group size and brain size in primates Mean Group Size 150 Chimp Humans Dunbar RIM, Br Acad Rev 2008;11:15-17. Neocortex Ratio

Examples of human social group size Social grouping Size Neolithic villages 7500 6500 BP 150-200 Roman army (military unit) 2000 BP 120-130 Tribal societies 148 Hunter-gatherer societies 165 Church congregations 200 Social network 134 Christmas card distribution list 154

The social brain in hominid evolution Grooming and its time/energy requirements Vocalization, wordless singing (H. erectus) Early social language (0.5 MYA) Grammatical speech (200 KY) Mind and culture foragers.wikidot.com/sexual-division-of-labor

Theory of Mind - Intentionality 1. I know what I am thinking 2. And I think I know what you are thinking 3. I think I know about what you are thinking about me 4. I think I know about what you are thinking about what I am thinking 5. I think I know what will happen if you don t respond in the way I want you to respond

Intentionality Predictions for Ancestral Hominins Achievable level of intentionality Millions of years BP

The Expensive Brain

Humans have big brains Human adult brain size 1350 cm 3 Human newborn 400 cm 3 Chimpanzee adult 400 cm 3 Chimpanzee newborn 160 cm 3

Humans have big brains Human adult brain size 1350 cm 3 Human newborn 400 cm 3 Chimpanzee adult 400 cm 3 Chimpanzee newborn 160 cm 3 The brains of a human newborn and an adult chimpanzee are about the same size

Proportional Brain Size and Development Brain growth (in terms of weight) finishes by about 7-8 years old Brain maturity isn t complete until about 25 years old!

160 cm3 400 cm3

Human Babies are are Fat Fat

% fat at birth Percentage Birth Fat for Mammals 16 14 12 10 8 6 4 2 0 Percentage Birth Fat for Mammals Kuzawa CW (1998), Yearbook of Phys Anthro, 41: 177-209

Girls Body fat % Boys Age (months)

Is baby fat an adaptation?

Percentage of total metabolic expenditure devoted to the brain in humans RMR allocated to brain (%) Birth 3 months 12 months 15 years Bodyweight (kg)

Diarrhea Body fat 3.1 2.8 2.3 1.5 1.2 0.5 birth 5 yrs birth 5 yrs

The problem Energy requirements after about 6 months of age exceed the capacity of breastfeeding But weaning onto solid foods carries the risk of gastrointestinal infection and interruption of nutrition So the extreme fatness of human babies might be an adaptation to protect energy supplies to the expensive brain

So, early human life is characterised by: Brain size at birth is the largest that can pass through the pelvic canal Rapid brain growth after birth High fatness in infancy to provide a reserve for the energetically expensive brain Fatness decreasing in early childhood as the infectious challenges of weaning are overcome These are early components of the human life history

The various evolved strategies that species use to convert energy from their environment into copies of themselves

Life history it s all about choices Grow fast or grow slow? Grow big or grow small? Eat meat, or go vegetarian? Live in the fast lane, or go with the flow? Lots of kids, or just a few? or

Human Life History

Cultural evolution

Biological versus Cultural Evolution Biological Transmitted as genes Natural or sexual selection Fitness measure is reproductive success Cultural Transmitted by stories, books, films, music.. Societal preference selects Fitness measure is utility or aesthetics

Features of human life history that facilitate cultural evolution Large brains Singleton pregnancies Postnatal dependency Long childhood (learning) Delayed sexual maturity Very few offspring, but most survive High parental investment High intergenerational transfer Longevity

Interplay between cultural evolution Social Group Development and biological evolution Technology Cooking Tools Shelter Ability to Utilise Niche Variation Biological Evolution

Success despite long childhood dependency

Discuss the potential adaptive advantage of bipedalism during the late Miocene period (approx 5-4 MYA) in eastern Africa that may have contributed to the development of bipedalism.

Discuss the relationship between the adaptive cost (metabolic and reproductive) of brain expansion and the adaptive advantage of the large brain.

Discuss the impact of key technologies on human evolution during the past 60,000 years and consider the potential influence of modern technologies on how humans might evolve in the future.

At the heart of selection is the concept of differential fitness, the idea that some individuals in a population have phenotypic characteristics that make survival and successful reproduction more likely than it is for other individuals. Yet we know that traits that might be expected to reduce fitness in human populations, such as the sickle cell anaemia, Huntington s disease or some of the adverse consequences of bipedalism, have not been eliminated by selection. Discuss the possible reasons why selection during human evolution has failed to eliminate traits that might lower fitness.

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Producer / Director Jos Ford Multicast Robert Hamilton Technical Manager Darren Tinkler Production Assistant Jamie McCarthy Camera Paul Richards, Luke Farmer, Mike Matheson Sound Andrew Lovrin, Seminar Chat Helen Mora, Anna Lehmann Writers / Presenters Michal Denny, Peter Gluckman, Alan Beedle, Tatjana Buklijas, Jacquie Bay LENScience Connect is Funded by the National Research Centre for Growth and Development LENScience Connect Liggins Institute University of Auckland 2010