Infanticide, Aging, and Death

Understand the 5 explanations for infanticide

Exploitation, infant is used as a resource, Resource Competition, infant death increases resources for another individual. Parental Manipulation, parents abandon or kill offspring. Sexual Selection, Killer is usually an unrelated male. Social pathology, Maladaptive, pathological behavior caused by stress, overcrowding, habitat encroachment.

What are natal coats for?

Natal coats in animals are: ● Brightly colored infant fur that differs from adult coloration ● Most common in highly polygynous colobines (where infanticide risk is high) Functions: 1. Protection from males ○ Attract attention of rest of the troop → others keep the baby safe ○ Creates paternity confusion ■ Males can’t judge resemblance → less likely to kill 2. Social signal ○ Encourages others to handle/help protect infants

What is the evidence for natal coats in humans?

Human babies may have a “natal coat” equivalent: ● Babies have anonymous, hard-to-read features at birth ○ Lighter skin ○ Less distinct face shape ○ Hair differences ● This may help conceal paternity ○ Avoids signaling cheating → adaptive in species with biparental care

What is the most common reason for infanticide in humans?

→ Parental manipulation due to scarce resources. ● Abortion (most common form of infanticide)

● Neglect during resource shortages

● Sex-selective abortion (India, China)

● Cases where the mother cannot afford to support an infant

● Ecology, economics, and culture are major factors Human infanticide is strongly correlated with:

● Poverty ● Harsh environments ● Sex-biased cultural practices (e.g., dowry systems, patrilineal inheritance) Other types also occur: ● Resource competition (e.g., stepparents → “Cinderella effect”) ● Pathology (rare) but parental manipulation is the most common.

1. Cultural variation in treatment of elderly

● Aging is associated with:

○ ↓ physical ability, ↓ attractiveness, ↓ new learning

○ ↑ wisdom, ↑ respect, ↑ knowledge

Negative views for elderly

● Found in societies with higher % of elderly individuals ● Reason: intergenerational resource conflict Treatment varies ● Some societies provide extensive end-of-life care ● Others practice eldercide in harsh climates or nomadic groups ○ Examples: ■ Chukchi of Siberia: elders request death or expose themselves ■ Ache (Paraguay): elders wander off or are killed ■ Nomadic groups: “voluntary death” via risky journeys

How is aging similar and different in humans vs. non-human primates?

Similarities: ● Dental decay ● Tooth loss ● Arthritis ● Injuries ● Behavioral slowing ● Some cognitive change Differences: ● Humans uniquely experience significant age-related brain volume loss ○ Likely due to our unusually long lifespan ● Humans live much longer after reproduction than other primates ● Humans maintain higher cognitive performance relative to physical performance

Evidence for longevity selection in humans

1. Hunter-gatherers live ~65 years once they reach mid-life (45+) → Long life is not a modern phenomenon.

2. No need for age correction in cognitive tests until ~60 → Suggests selection for maintaining cognition late in life.

3. Brain size and longevity are correlated across mammals → Humans follow the ape trend; long life fits our brain size. 4. ApoE gene evolution ○ Humans have ApoE2 and ApoE3—protective variants ○ ApoE4 (ancestral) linked to Alzheimer-like pathology → Selection favored genes that maintain brain health in older age.

5. Grandmother effects ○ For grandmothers to help, older individuals must remain cognitively capable.

6. Social information reserves ○ Brain stores knowledge about resources, ecology, crises ○ Older individuals with experience could help group survival → selective advantage

Knowledge of death in non-human animals

✔ Awareness of another individual’s death as a significant event ✔ Behavioral changes around corpses: ● Elephants: linger, touch bones, show agitation ● Dolphins/orcas: carry dead infants, lift bodies to the surface ● Primates: mothers carrying dead infants, touching bodies ● Crows: gather around dead conspecifics ● Ants: remove dead members (chemical cue) What they likely do not have: ✘ Awareness of their own mortality ✘ Evidence of belief in an afterlife ✘ Symbolic mortuary rituals

Neanderthal burials: evidence of ritual or afterlife?

Neanderthals DID bury their dead intentionally. ● Bodies placed in pits ● Often in flexed “fetal” positions ● Some burials covered with stone slabs. EVIDENCE: ● Teshik Tash: ibex horns placed around child ● Shanidar Cave (“flower burial”): ○ Pollen found → maybe flowers buried intentionally (but possibly rodents) ● Some grave goods (tools, bones) but might have fallen in later

Early evidence of mortuary rituals in Homo sapiens

1- Herto, Ethiopia (~160 KYA) ● Cut marks on skulls ● Skull polishing / handling → Probably ritual defleshing → funerary ritual

2- Qafzeh Cave, Israel (~100 KYA) ● 13 individuals (including children) ● 71 pieces of ochre only with burials → Suggests symbolic meaning (possibly belief in afterlife)

Modern human mortuary rituals

Mortuary rituals are universal among humans. They often involve practices like burial or cremation, symbolic gestures, and the inclusion of grave goods, reflecting cultural beliefs about death and the afterlife.

Endocannibalism

The practice of eating the flesh of a dead person from the same community, often as a form of honoring the deceased. This ritual can reflect beliefs about death and connection to ancestors. Examples: ● Yanomamö: mix ashes with banana soup ● Fore of Papua New Guinea ● Even Christian Eucharist is symbolically similar (consume “body and blood”)

Mummification

The process of preserving a body after death through techniques that can include drying, embalming, and wrapping, often for the purpose of ensuring the deceased's journey in the afterlife. Historically practiced in various cultures, notably ancient Egypt. : ● Ancient Egypt (humans + sacred animals) ● Tana Toraja (Indonesia): keep mummies at home, treat them as “sick” until ceremony ● Inca mummies

Inhumation

The burial of a deceased individual in the ground, often in a grave, as a common mortuary practice across cultures. Inhumation reflects beliefs regarding the body and the afterlife. Burial of body in a grave or tomb ● Most common in modern societies ● Influences the type of archaeological evidence we look for