Lesson 2 Flashcards
Defining traits of homosapiens
Bipedalism: Walking on two legs. Efficient for long-distance travel and freeing the hands, but causes challenges like back pain and difficult childbirth.
Large Brains: Allow for abstract thinking, problem-solving, social complexity, and language.
Language: Unique among animals due to grammar and infinite expression. Facilitates cumulative culture— building knowledge across generations.
Extended Life History: Long childhood allows learning complex skills. Long post-reproductive life (e.g.,
grandparenting) is rare among animals.
Evolution of bipedalism
Earliest evidence: Orrorin tugenensis (~6 mya).
Clear evidence: Australopithecus afarensis (“Lucy”, 3.2 mya).
Adaptations:
Shifted foramen magnum (base of skull) for upright posture.
Bowl-shaped pelvis, angled femurs, and arched feet.
Knee lock for stability.
Costs: Increased injury risk, difficulties in childbirth, and joint wear.
Culture is
Cumulaltive: We rely on socially learned behavior for survival (e.g., how to cook, build shelters).
Example: 1860 Burke & Wills expedition in Australia — failed despite supplies because they lacked indigenous knowledge.
Human culture is cumulative: builds complexity over time (e.g., smartphones, medicine).
Evolution of language
Animals like dolphins and monkeys have communication, but lack grammar.
Human language allows us to share imaginary ideas (e.g., “blue giraffe”) and pass down culture.
Language likely co-evolved with social behavior and brain complexity.
The human genome
Humans share 98.77% of DNA with chimpanzees.
Differences are mostly in gene regulation and scale, not entirely new genes.
Most traits are quantitative (vary by degree) rather than binary.
Human evolution timeline
7–4 mya: First bipedal hominins.
2 mya: Homo erectus — tall, tool use, long-distance travel.
300 kya: Homo sapiens — large brain, symbolic thought, modern behavior.
Expensive tissue hypothesis
Expensive Tissue Hypothesis: Our large brains consume a lot of energy, so gut size had to shrink — making us dependent on high-energy foods.
Cooking food increases energy absorption and reduces digestion effort.
Human diet is omnivorous, but varies widely based on environment and culture.
Growth in body size
Over 4 million years:
Brain size: 3× increase.
Body mass: 2× increase.
Height: +40–50%, mostly in legs.
Linked to mobility, endurance, and survival in diverse climates.
Growth implications for health
Bipedalism → joint issues, childbirth risks.
Large Brains → mental health vulnerabilities, stress (Week 11).
Fat Storage → advantageous during food scarcity, but can lead to metabolic diseases today (Week 8).
Cultural Engineering: We alter our environments (houses, roads, farms), but this can outpace our ability to adapt biologically.
Humans depend on _____
Culture!! This is true in the Robert Burke story where he traded with locals for survival while on an expedition across Australia.
What is thermoregulation
Apocrine glands – maintain coat
Eccrine glands – secrete water, salt
Quadrupeds
stand/ / walk on four legs– large supporting rectangle
formed by the outer margins of their feet
– easy to maintain balance
Bipedalism in chimpanzees
Inefficient energy
expenditure due to
muscle activity
(hamstrings) to maintain
mechanical advantage
• to increase efficiency:
A) decrease the angle
between ilium and
ischium
B) increase spinal
curvature
C) knee lock
Gait
The walking cycle
Stride
From heel strike to heel strike
Stance phase
Weight suppported by legs
Swing phase
Leg is bought forward fr next heel stike
Australopithecus afarensis – 1974, Hadar, Ethiopia
Hadar, Awash Valley of Ethiopia’s
Famous ‘Lucy’ fossil - 3.2 MYA
• Femur head and neck like ours
• Short arms, long legs
• Wide and short pelvis
• Anterior shift of foramen magnum
• Valgus angle of knee
• Still small brain (380cc)
Explanations of Bipedalism
Indirect explanations:
- Thermoregulation
-Tool-making, Carrying, Provisioning,
Postural feeding: ‘freeing the hands’
Direct explanations:
- Energetic Advantages
- Highly efficient mode of terrestrial
locomotion
- Greater day ranges, time budgets,
access to resources
Consequences of a bipedal body
Why is it important to health?• Reorientation of joints,
body make:
– pregnancy and childbirth
difficult (week 6)
– us susceptible to new kinds of injuries (week 12)
– different energy acquisition and metabolism (weeks 8,9)
The earliest ‘human’ - Homo erectus
New terrestrial species, 1.8 mya
• Tall (170-180 cm) and relatively short arms
• Less differences in size between males and females
• Developed new tools and hunted large game
• Smaller brains than modern humans, and less flexible behaviour
Stone tools fo homo erectus
The earliest tools are Oldowan, from 2.6 – 1.6 MYA
• Between 1.6 – 1.4 MYA, developed more
sophisticated tools: Acheulean
• Key features include: – Stereotyped tool forms from entire stone
– Cutting surfaces on both sides (Bifacial) Oldowan• Larger size, 15 - 30 cm in length
• Likely used in butchery
Climatic conditions
First species of ‘us’ to migrate out of Africa
• Long glacial periods punctuated by short,
warmer, interglacial periods
• During glacial periods, Africa and Eurasia were
separated by a massive desert
• During warmer periods massive grasslands
between Africa and Eurasia.
• Mobility – Persistence Hunting – adaptations
to heat stress – hair loss, sweating
Dietary comparisons of the
primates:
- Most species are predominantly frugivores (fruit)
- Most variation along axis of folivory (leaves) /
faunivory (animals and insects)
Frugivory
True omnivores rare
Humans fill this role, but only
through cooking of food
Breaks down cellulose, toxins,
and releases more energy
