Evolution of Behavior

A. Genes and the inheritance of behavioral characteristics

• Characteristics that are inherited biologically do so through genes

• Genes affect behavior by building and modifying physical structures of an organism. Those structures then interact with the environment, producing behavior.

• Not all genetic changes occurred because they helped the organism to adapt to new environmental circumstances, e.g. genetic drift

Evolution of Behavior

behavior can have a genetic basis

genetically-based differences

affect fitness

evolve by natural selection

Species 1

Species 2

Hybrid

Cricket Song Pattern

B. ETHOLOGY: The study of species-typical behavior patterns

• focus is on behavioral differences among species that could reflect their evolutionary heritage

• Fixed Action Patterns (FAPs) > Motor program that is "hardwired“

> Involves a repertoire of stereotyped movements > behaviors are characteristic of a species and their structural features

> sign stimuli: those stimuli (e.g., red belly) that elicit the FAP (e.g., attack)

(Are red sports cars sign stimuli for road rage??)

Examples of FAPs and sign stimuli:

• Tinbergen's stickleback research: Red underbelly serves as sign for vigorous attacks by other male sticklebacks

• Human yawning (releases yawns in others)

• Human smiling (releases smiles in others)

• Human eyebrow flash

• Baby schemas

Lorenz' research on Baby schemasCertain stimuli indicating "babyness" release an innate tendency by us to feel sympathetic distress and to care for the young.

Some of releasing stimuli discussed are: • Proportionately larger head than body. • Forehead that protrudes relative to rest of face. • Extremities that are short and thick. • Round body shape. • Soft elastic body surface. • Chubby (round) cheeks.

Some ethologists note a connection between baby faces and sexual attractiveness.Why would there be a connection, do you think?

Why Study Fixed Action Patterns?

FAP help us to figure out how behaviors/characteristics evolved, since FAPs are slightly different in species that are related to one another

More importantly, not all behavior should be seen as rigid or inflexible fixed action patterns in response to sign stimuli. The characteristics that we inherit biologically "prepare" us to be able to quickly learn some behaviors and less quickly learn (or never learn) others. • humans seem biologically prepared to learn a language or walk on two legs • bats and sharks to sonar• dogs are sensitive to more smells and sounds

C. Tracing the Evolution of Species Specific Behaviors

• think of evolution in terms of a HUGE tree with multiple branches: > trunk represents the common heritage we share > the tree branches off in different directions and branches off again and then branches off again (...). > any limb connecting two branches means shared common ancestor (e.g., lions and tabby cats have the same great- great- great-...grandparents). > but, at some point on the tree the organisms have split off and gone in different genetic directions

We can graph what the tree of evolution looks like (where it branches; where organisms split from one another) by studying similarities among species.

Gray distinguishes two types of similarities:

1. Analogies2. Homologies

1. Analogies > similar characteristics reflecting convergent evolution > two species share a characteristic, BUT NOT because of a common ancestor passed along the characteristic to the species > two evolved the characteristic because of some similarity in their habitats or lifestyles > an adaptation in that environment > the similarities are often in function and gross form of the characteristic. Closer look, very different Examples: Dolphins, fish, and penguins have fins Bats, birds, and mosquitoes have wings Elephants, boars, and walruses have tusks Snakes and bees produce venom Ostriches, giraffes have long necks Ducks and otters have webbed feet

2. Homologies > Similar characteristics reflecting a common ancestor > two species share a characteristic, BECAUSE of a common ancestor > obviously, which species will show a greater number of homologies?

Examples > Vertebrae > Two eyes > Noses, mouths, teeth, ears, limbs, skin

homologies shared genes similar underlying physiology and construction even though "on the surface," they may appear different and may function differently

D. Sociobiology: The comparative study of animals' social systems

Why do organisms engage in aggressive behavior? What functions does it serve?

Territorial Aggression vs. Dominance-Related Aggression

Infanticide in lions:

aberrant or advantageous?