Introductory Biology

36.1 Evolution of Behavior (Part 1)

Why are humans nice?  A behavior is an action performed by an animal in response to a stimulus. (Examples: a frog jumps into a pond to avoid a predator) Stimulus can be something in the environment, like a sound, smell, color, or another individual and can relate to the internal state of the animal, such as being hungry or cold. (Examples of stimulus: lizards flares folds of skin around its head when under threat; gives threatening look that tells potential enemies to back off)  Scientists who study behavior research two kinds of questions- how and why. “How” questions are about how a behavior is triggered , controlled and performed. “Why” questions states the reasons a behavior exists (are about the evolution of behavior). We know that genes and the environment have influences on behaviors –> Genes + Environment = Behavior.

Behavior is altered by natural selection, which favors traits that improve the chance than an individual will survive and reproduce. Traits that give a reproductive advantage over time become more common and increase. EXAMPLE: East African lions. Lions live in groups (prides) containing several adult females, young cubs, and one/more adult males. Adult males father the cubs and defend the territory, but may be defeated by other males from different areas. Males want to take over the pride to mate with all the females. When the invading males takes over a pride, they usually kill all the cubs that ore not theirs, to ensure that his own genes are passed on and can produce their own offspring sooner. Behavior can be understood from costs and benefits. Some males that don’t kill cubs that are not their own, will have to wait until the cubs mature before the females will mate with them so he can produce his own cubs. All males use the strategy of killing other’s cubs will be selected for, and the strategy of being tolerant of other’s cubs will be selected against. Scientists later agreed that natural selection favors traits that contribute to the survival and reproduction of individuals (not species). Some animals, like the Langur, avoid infanticides by tricking the male: the mother hiding her kids with her sister, showing color representing that she can mate, and after she mates with the male she gets back her kids.

Innate behavior (or instinct) is genetically programmed behavior. When mating, ducks that are not able to dance very well were neglected and did not pass on their alleles. Female sickle back fish are more attracted to healthy strong males that are good at getting food (having a red stomach indicates healthy body). Many behaviors are heritable, known to be affected by genes or set of genes (variation, types of dance…). Fixed action pattern behavior  is the innate behavior that always occur the same way. Fischer’s lovebird hybrids experiment demonstrated the genetic basis of next-building. Nest building is an innate behavior for most birds, like the African lovebirds that carry materials back to its site to make a nest. One species of Fischer’s lovebirds carries one long strip of nesting material in its beak. The other peach-faced lovebird carries some short strips of nesting material in their feathers. Evidence of innate behavior is shown in studies that two types of lovebirds were interred. Their hybrid offsprings showed both parents nesting behaviors: carrying medium-length strips of nesting material unsuccessfully  trying to put them in their feathers. Later on, some birds learned to carry the material in their beaks. EXAMPLE: The dihybrid cross between two breeds of dogs, border collies and Newfoundlands, that have different genes but similar enough to have offsprings. Complex behaviors can be genetically controlled. Regardless of the environment, all members of that group show the same behavior. 9 – 3 – 3- 2 are pure bred. 9/16: both dominant alleles, offspring show both behaviors. 3/16: one dominant allele. 3/16: other dominant allele. 1/16: no dominant allele.

Altruistic behavior: sacrificing themselves to save others. Bees, ants, wasps, and termites show this behavior. They are very successful and cooperate with each other. “Blood is thicker than water” applies to them (family is more important than others). EXAMPLES:

  •  Bees sacrifice their lives by stinging intruders to save the beehive and the queen bee. The males are haploid- unfertilized eggs and they only have a half set of genes.  (Male and female humans are both diploids -> equally related) Bee sisters are 75% related to each other while, brothers are only 25% related. Frequency of alleles over time. An allele that helps genes of same kind will increase, that behavior causes more of the genes to be passed on. Reason why they are so nice to each other, especially the sisters because they are very closely related. Some fixed action pattern behavior can be seen in worker bees: workers build hives, raise young, and the adult females collect nectar and pollen. The social organization of honey bees: 30,000 workers which are sterile and one fertile queen, the sisters act as a nurse, house keeper, a guard, and collect food.
  • Vampire bats: act altruistically towards others/friends. They need to eat once every 3 days or else they will die from starvation. In one meal, they can gain 1/3 of their weight. When one comes back from a meal, it goes to a friend and regurgitates for the friend. (Huge advantage to the recipient).

Human Altruism: firefighters put their won life at risks for people they are not related to.

Reciprocal altruism: friendship, only works if they have a long-term friendship. Example: bats – the amount of time bats spend roosting next to each other shows high association value (Most animals do not share food).

Kin selection: it does not matter so much that their own genes survive, as long as others with the same genes survive (the donors behavior that benefits recipients relatives at cost to self). It is one aspect of being nice. The cost of the nice person pays, compared to the recipient = is the function that they are related to.  R > fitness costs to altruists/ fitness benefits to recipient. Altruistic donors: loose genes and gets nothing back, gets smaller. Altruistic recipients: benefits, gets bigger. Example: In prairie dog families, one screams like a warning call when halks or any predators come.  It is likely to act more altruistically towards each other if they are closely related. 


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One thought on “36.1 Evolution of Behavior (Part 1)

  1. Yurika,

    Great job with your entry for 36.1 on the evolution of behavior. You’ve covered all the ideas brilliantly!!

    Mr. F.

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