8. Human Evolution Flashcards
(40 cards)
How is Earth’s 4.5 billion-year history compressed into a “calendar year,” and where do humans and the Industrial Revolution fall on that scale
Humans appear in the last 24 minutes of December 31
Industrial Revolution occupies the final 2 seconds
What is cumulative culture, and why is it considered key to human success?
Definition: The ability to faithfully transmit knowledge and practices—via precise imitation skills—so that each generation can build improvements on prior innovations
Contrast to other animals: While many species imitate, only humans reliably preserve and refine techniques over generations
How does cooperation—illustrated by 19th-century Arctic expeditions—highlight human cultural success?
Cooperation: Flexible collaboration toward shared goals, even with strangers
Arctic example:
Franklin’s expedition (1845): No Inuit partnership → all perished
Ross expeditions (1818–29): Allied with Inuit → survived two winters
Lesson: Learning survival skills through cross-cultural cooperation can mean the difference between life and death
How did tectonic and climatic changes in East Africa drive early hominin speciation?
East African Rift: Plate movements created new valleys and highlands
Climate shifts: Increased aridity and dramatic wet–dry cycles
Outcome: Forest fragmentation into open savannahs → populations became geographically isolated (allopatric speciation)
What key anatomical and life-history traits distinguish genus Homo from other apes?
Bipedal posture: Major skeletal adaptations for upright walking
Dentition & jaw: Reduced prognathism and smaller molars
Precision grip: Enhanced fine-motor control in the hand
Brain enlargement: Significantly larger cranial capacity
Extended childhood: Longer juvenile period with slow development
Cultural reliance: Dependence on material technology, symbolic behavior, and high cooperation
What advantages did bipedal walking confer on early hominins?
Thermoregulation: Reduced sun exposure; better cooling
Freed hands: Carry food, tools, and offspring
Vantage: Easier to scan tall grasses for predators or prey
Energy efficiency: More economical over long-distance travel
Which innovations and behaviors mark Homo erectus, and when did they spread beyond Africa?
Body & brain: ∼60% of modern human brain size; taller, more robust build
Dietary shift: Greater reliance on meat—scavenging and hunting
Tool use: Stone tools for extracting and processing carcasses; defended kills cooperatively
Life history: Longer juvenile phase to learn complex skills
Sociality: Enhanced cooperation in groups
Geographic range: Dispersed into Eastern Asia by 1.8–1.6 Ma
Where and when do the oldest Homo sapiens fossils appear, and what innovations distinguish them?
Fossil sites: Morocco (~300 ka) and Ethiopia (~200 ka)
Key innovations:
More advanced stone tools and social behaviors than contemporaries in Europe/Asia
Control of fire by ~400 ka (cooking evidence possibly as early as 700 ka)
When did major Out-of-Africa migrations of Homo sapiens occur?
Primary exodus: ~60 ka (thousand years ago)
Possible earlier dispersal: ~120 ka
Drivers: Climatic fluctuations (900–130 ka) creating new migration corridors
How did Homo sapiens interact with resident hominins after leaving Africa?
Overlap period: Neanderthals occupied Europe/Western Asia from ~400 ka to ~40 ka
Replacement with gene flow: Modern humans largely replaced Neanderthals by ~30 ka but interbred, leaving Neanderthal DNA in non-African genomes
Outcome: Anatomical and cultural modernity spread, aided by small genetic exchanges
How did environmental and subsistence challenges in Pleistocene Africa drive the evolution of human cooperation and cumulative culture?
Open, risky foraging niches: Tubers, seeds, scavenged meat required complex extraction skills learned from others
Carcass defense & hunting: Coordinated groups defended kills from predators and cooperated on hunts
Outcome: Enhanced imitation and faithful transmission of knowledge—cumulative culture—allowing incremental improvements in tools and techniques
What is cooperative breeding, and what derived social–cognitive traits did it select for in humans?
Cooperative breeding: Alloparental childcare evolved as infants became more helpless (longer juvenile period, complex diet)
Social consequences: Babies needed to engage with multiple caregivers, fostering:
Joint attention
Enhanced social motivation and temperament changes
Early-developing social skills for interacting with diverse adults
Which capacities underlie shared intentionality and group-mindedness, and how do they shape large-group cooperation?
Shared intentionality & joint planning: Coordination on common goals (Bullinger et al., 2011)
Leader–follower strategies: Flexible roles to organize group action
Group-mindedness: Cultural practices, social norms, and markers of identity (“speak like me,” “eat like me”) to:
- Identify reliable collaborators
- Signal one’s own cooperativeness
- Deter free-riding in larger bands and tribes (Tomasello et al., 2012)
How do humans detect coalitions and develop social preferences, and what does this imply about race versus language cues?
Coalition detection: Cognitive machinery encodes alliances––any salient feature (e.g., uniform color) can cue group membership (Kurzban et al., 2001)
Social preferences:
Language preference emerges by 10 months; race preference by ~2.5 years (Kinzler et al., 2007; 2011)
By age 4–5, shared language overrides racial category in who children prefer
Implication: Language, not race, was the more reliable ancestral cue to coalition
What characterizes in-group favoritism in children, and how does it develop relative to out-group derogation?
In-group love appears early (≈6 years old): children preferentially allocate resources to in-group members (Buttelmann & Böhm, 2014)
Out-group harm emerges later (≈8 years old) and follows in-group favoritism rather than preceding it
Insight: Cooperative interdependence fuels positive biases toward one’s own group before any negative sentiments toward outsiders
women and childcare duties
In April to June 2019, 3 in 4 mothers with dependent children (75.1%) were in work in the UK. This compared with 92.6% of fathers with dependent children.
-Almost 3 in 10 mothers (28.5%) with a child aged 14 years and under said they had reduced their working hours because of childcare reasons. This compared with 1 in 20 fathers (4.8%).
-Many of these effects exacerbated during COVID-19.
Humans as unusual mammals
- A group in which breeding females are solitary in 68% of species, socially monogamous in 9% of species, and live in social groups in 23 % of species
.-Infant care is performed exclusively by the female in more than 90 % of mammal species.
-Humans are rather unusual among the primates and great apes in that fathers provide any care at all.
What do cross-cultural studies reveal about the impact of mothers versus fathers on child survival?
Mother’s presence positively affects child survival in 100% of 45 natural-fertility populations (Sear & Mace, 2008).
Father’s presence has no detectable effect on child survival in 8 of 15 studied populations.
How do paternal caregiving behaviors contrast between the Hadza and Datoga of Tanzania?
Hadza men: Engage extensively in childcare (playing, holding), reflecting a cooperative foraging lifestyle.
Datoga men: Consider childcare “women’s work,” prioritizing livestock herding and polygyny over child-rearing.
What explains variation in paternal care—and its trade-off with mating effort—across human societies?
Mating vs. parenting trade-off: Men allocate effort between seeking mates and investing in offspring.
Testosterone links: Higher basal T correlates with reduced paternal caregiving and greater mating effort across species—including Datoga and Hadza men.
What is paternity uncertainty, and how does it influence paternal investment?
Paternity uncertainty: Fathers can never be 100% sure that offspring carry their genes
Evolutionary implication: Investing heavily in non‐genetic offspring is maladaptive
Result: Men evolved sensitivity to cues of genetic relatedness before allocating high parental investment
How does anisogamy shape male and female reproductive strategies?
Anisogamy: Females produce few, large gametes; males produce many, small gametes
Limits:
Females: Reproduction constrained by resources and gestation
Males: Constrained by access to fertile mates
Sexual selection pattern: “Ardent males, choosy females”—males compete for mates; females select high‐quality partners
How does the mating–parenting trade-off interact with the adult sex ratio to determine paternal care?
Trade-off: Males allocate energy between seeking additional mates (mating effort) and investing in offspring (parental effort)
Adult sex ratio effect:
Female‐biased ratio (more eggs/mates available): Males favor increased mating effort over care
Male‐biased ratio (more sperm/competition): Males invest more in their existing offspring and partner
According to Schacht et al. (2017), how did adult sex ratios drive the evolution of social monogamy and paternal care?
Female‐scarce environments: Males “stick” with any partner, defend her—selective pressure for social monogamy (co‐habitation, shared resources, joint parenting)
Female‐abundant environments: Males invest in mating effort, little in offspring
Evolutionary sequence: Social monogamy evolves first; paternal care emerges as a by‐product once stable pair bonds exist
