Lecture 14 ASM

Altruism refers to behaviors where one individual (the altruist) incurs a cost to benefit others.
An example of altruistic behavior is alarm calling in primates, where an individual warns others of a predator.
- Calls benefit the listeners who can escape, but the caller risks increased predation due to conspicuousness.
- Conspicuousness: The trait of attracting more attention, potentially making the caller more vulnerable.

An example of a monkey alarm call during a predator threat:
- Observers noted a situation where one monkey kept calling even after others had retreated, culminating in its demise after a strangulated call.
- This highlights the risks involved in altruistic signaling.

The discussion introduces a hypothetical scenario with two alleles at a genetic locus:
- Altruistic allele: Produces alarm calls when predators are spotted.
- Alternative allele: Results in silence, allowing the individual to escape without alerting others.
Alarm calling is altruistic as the callers incur a personal cost, yet the group benefits.

Fitness: The genetic contribution of an individual to the next generation.
- In the case of altruism, we need to assess whether the act of calling ultimately benefits or harms the caller's fitness.
Initial group frequency of altruists (those with the altruistic allele) was 0.25 (2 out of 8 individuals).
The discussion reveals:
- Callers reduce their fitness by making themselves conspicuous to predators.
- Non-callers gain survival benefit from the alarm call without incurring any cost.

The question arises whether selection can favor altruistic behavior considering the fitness costs to the caller.
While the intuition might suggest that altruism must benefit the entire group, this theory struggles to justify its occurrence from a Darwinian perspective.

The paradox states: Altruism exists, but evolutionary theory suggests it cannot.
The need arises for a deeper understanding and a potential resolution to this paradox.

William D. Hamilton’s Contributions: In the 1960s, Hamilton proposed that altruism could evolve under certain conditions when individuals interact preferentially with their genetic relatives (kin).
Kin Selection: The evolutionary strategy that favors reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction.
Animals do not interact randomly; instead, they are often grouped with relatives (e.g., full siblings).
In groups of full sisters, the likelihood of sharing an altruistic allele increases, allowing altruism to be favored.

Groups based on genetic relatedness can lead to higher frequencies of altruistic alleles being passed to future generations.
In a hypothetical case with groups of sisters, they would share more genetic material, enhancing the success of altruistic behaviors.
Mathematical Model: A proposed condition for altruism to evolve is encapsulated in the equation:
- r imes b > c
- Where:
- $r$ = genetic relatedness between the actor and the recipient
- $b$ = fitness benefit to the recipient
- $c$ = fitness cost to the actor
When relatedness increases, altruism becomes more likely to rise in frequency within populations.

As $r$ decreases (becoming less related), it becomes harder for the inequality to be satisfied, thus making altruism less likely to evolve.
Conversely, the closer the kinship, the more the altruistic behaviors can evolve as the fitness costs are offset by the benefits to genetically similar individuals.
Altruistic behavior can be observed more strongly in immediate family (identical twins have $r=1$ , full siblings $r=0.5$ ).

Animals have evolved mechanisms to recognize kin beyond just genetic clues:
- Familiarity: Individuals learn who their relatives are through close association.
- Age Similarity: Animals often spend more time with peers close in age, which might indicate the likelihood of shared parentage.
- Phenotypic Cues: Similarities in physical traits, calls, and even smell can assist in identifying relatives.

Nepotism: Preference for aiding relatives, seen across diverse animal behaviors.
Though typically viewed negatively in human contexts, nepotism underscores natural social structures and cooperative behaviors observed in species, especially primates.

Examples from primate social structures suggest that maternal behaviors influence offspring development significantly.
Maternal rank inheritance and support in primate social groups highlight the importance of kin in cooperative behaviors and making predictions about ranks in social hierarchies.
Patterns of grooming, resource sharing, and protective behaviors contrast with the intuitive notions of altruism in human society.

Animals typically display cooperation that aligns closely with biological kinship.
The evidence strongly supports the idea that genetic relatedness plays a crucial role in structuring cooperation and altruistic behavior in nature.

Understanding the evolutionary basis of altruism through kin selection offers insights into cooperative behavior across species.
Exploring the mechanisms of kin recognition provides a broader perspective on how social structures are established and maintained in various animal societies.