Altruism in Forest Chimpanzees: The Case of Adoption Boesch , et al.

1. Altruism in Forest Chimpanzees: The Case of Adoption Boesch, et al. Amanda, Caitie, and Alex

2. Introduction • Altruistic interactions: • costly to the actor, beneficial to the recipient • Evolutionary theory predicts limited to kin and reciprocating partners • Altruistic interactions with non-kin had been thought to be uniquely humans • Motivating factors: punishment by one’s peers, improved reputation

3. Introduction (cont’d) • Captive chimp studies • Showed “limits in the way individuals were able to share or cooperate with others, espeically [with] food” • Thought to be an important difference between humans and chimps • However: • Reports of altrusitc behaviors exist in wild chimps • Reported covering various domains: food sharing, regular use of coalitions and cooperative hunting and border patrolling

4. These differences beg the question: • What socio-ecological factors favor the evolution of altruism [within a species]?

5. Methods • Ongoing daily observations at the Taï National Park, Côte D’Ivoire • 3 decades; up to 4 neighboring chimp communities • North community: 1982 • South community: 1993 • Middle group: 1995 (reduced in 2004) • East group: 2000

6. Data Collection • Daily demographic information collected by trained field assistants and students • Standardized check sheets, gathered: • Party composition, party size, any changes to either; basic social interactions • Detailed adoption info gathered ad libitum as event occurred and with mother-infant check sheets • Further evidence gathered with social interaction check sheet: • Food sharing, support in aggression, and co-nesting

7. Hamilton’s rule proposes altruism should be favored under two conditions… When the cost of the altruistic act is compensated by the genetic relatedness between the giver and the receiver. When the cost of the altruistic act will be compensated at a later time through reciprocation. It’s displays of altruism toward unrelated individuals that (supposedly) makes humans unique.

8. Comparison studies of 15 human societies show that levels of altruism vary with group size and the level of market integration. • Following Hamilton’s Rule, we would expect more altruism in populations of individuals, where the benefit becomes larger than the cost. • Given this, the lack of altruism in food sharing displayed in captive chimps may be due to the well-fed state of the subjects. In natural conditions we might expect many situations where altruism would benefit the group.- Food sharing.- Adoption.- Defense against predators.

9. The link between kinship and altruism in chimp social groups is rather weak, which doesn’t support condition one. • The second condition is more difficult to evaluate because the reciprocation can take place over a long time. • (For example: male chimps exchanging food for mating rights.)

10. One example of altruism in chimp social groups is adoption of orphans by group members in forest chimpanzees in the Tai National Park • Some of these adoptions (often by unrelated adult males) lasted for years.

11. Adoption was defined as any relationship between an adult and orphan (infant or juvenile) in which the adult shows species-specific maternal behavior for at least a two month period. • The adult must also be permanently associated with the orphan and display certain altruistic behaviors.- Sharing food.- Waiting for the orphan when traveling.- Protecting them in conflicts. • These are altruistic behaviors because they are costly to the adult but highly beneficial to the orphan. Un-adopted orphans rarely survive, and if they do may display some physical retardation.

12. In 3 communities observed over 27 years, 36 cases of orphans surviving for two months after the loss of their mother were observed. In 18 of those cases an adoption took place. • 8 adoptions were performed by females, including 1 by an older sibling and 3 by possibly unrelated “friends” of the mother. In general, though, the presence of kin did not increase the likelihood of adoption. • In 2 cases, adult females breast fed unrelated young infants. • An equal number of male and female infants were adopted and orphans adopted by males rather than females did not differ in sex or age.

13. Adoptions by Males • 1 of the adoptive males was the actual father • 3 adoptive males were unrelated • 2 were of unknown relation to the orphan • Main roles of male chimps: • Main hunters for the group • Actively defend territory from intruders • Typically do not exhibit paternal behaviors!

14. Altruistic Behaviors • Wait for during travel, provide protection, and share food with the orphans • Carried unweaned chimps dorsally during travel for many months • Held them in risky situations • Shared food • One male even share his night nest (very rare!) • Costs of Adopting: • Notable time and energy investments • Harassment • Orphan survivorship does not increase

15. += engaged in behavior - = did not engage in behavior ?=unknown

16. Benefits of Adoption to the Orphans • Risks of orphan chimps: • Typically do not survive to adulthood • Suffer retardation in physical development • Benefits of Adoption: • Receive support, care, food, etc. • In this particular study, chimps adopted by the Alpha male matured and showed no sign of retardation (meaning they benefited dramatically!) Figure 2. Orphans adopted do not present higher likelihood of surviving.

17. Benefits of Adoption to the Adult Chimps • Male orphans could become an ally to the adoptive adult male. • This does not apply to the adoption of female orphans • Improved reputation • However that should make them more reproductively successful, but in this study that wasn’t necessarily the case.

18. Conclusions • “Altruism is not hard wired and will be directed specifically towards individuals that profit significantly from this act”(Boesch et al. 2010) . • “Contrary to earlier sweeping conclusions, chimps are sensitive to the welfare of unrelated group members”(Boesch et al. 2010) .

19. “Altruism in the case of adoption in forest chimps seem to be the outcome of the specific socio-ecological conditions faced by the individuals” (Boesch et al. 2010) • Captive situations may not be the best place to test because it guarantees that all individuals have a safe environment and access to food, which may not mimic situations in which the welfare of others is an issue • Tai population may differ from other well-studied chimp populations because they coexist with a large population of leopards and the resulting high predation.

20. The End