Simple behaviors include growth movements (tropisms) and
locomotor movements (taxes, kineses). Complex innate behaviors are
called instincts; they tend to be inflexible, and no time is
wasted in learning them. Learned behaviors vary more with circumstance, but
a learning period is a necessary prelude.
SIMPLE BEHAVIOR PATTERNS:
Tropisms are growth or turning movements in
plants or sessile animals. Tropisms and taxes directed toward a
stimulus are called positive; those directed away from the stimulus
are called negative.
- Phototropism: growth or turning toward light (positive phototropism) or
away from light (negative phototropism).
- Geotropism (gravitropism): growth toward or away from the earth's center.
- Chemotropism: growth toward or away from a chemical; special types
include halotropism for salt or hydrotropism for water.
- Anemotropism: growth toward or away from a source of wind.
- Thigmotropism: growth toward or away from something touched.
Taxes: Oriented locomotor behaviors.
- Phototaxis: motion toward or away from light.
- Geotaxis: motion toward or away from the earth's center.
- Chemotaxis: motion toward or away from a chemical; special types include
halotaxis for salt or hydrotaxis for water.
- Anemotaxis: locomotion upwind (positive) or downwind (negative).
- Rheotaxis: swimming upstream (positive) or downstream (negative).
Kineses: Non-oriented locomotion, with no particular direction.
- Photokinesis: locomotion in response to light.
- Chemokinesis: locomotion in response to chemicals.
- Thigmokinesis: locomotion in response to touch.
COMPLEX BEHAVIOR PATTERNS:
Instincts: Complex, innate behavior patterns.
- "Complex" means that several acts need to be done in proper succession.
- "Innate" means inborn or genetically programmed. A standard test is whether animals raised alone
from birth can perform the behavior correctly. Song birds, for example, can be raised from hatching
in a soundproof room with no opportunity to hear the songs of other birds, but, when they become
sexually mature, they will sing the correct mating song of their species and sex!
- Usually stereotyped, meaning that the behavior does not
vary from one occasion to another or one performer to the next (good for
courtship and species-recognition behavior).
- Advantage: No time or effort is wasted in learning or in making mistakes;
behavior is correct the first time.
- Disadvantages: Cannot be modified to suit circumstances.
- Examples: Many aggressive or submissive postures and movements;
courtship and mate-attracting behaviors (bird songs, frog croaks, cricket chirps, etc.), nest-building
behaviors in many species, web-weaving in spiders, territorial defense.
Illustrations
Learned behavior: Behavior that improves with practice. Learned
behavior is more variable, an advantage in interactions with the local environment,
but a disadvantage in mate recognition or courtship.
- Advantages: Can be varied to suit local circumstance; can become
more complex than instincts.
- Disadvantages: Learning (and mistakes) must take place first;
youthful inexperience is a price.
The amount of possible learning is limited by neural complexity.
Imprinted behavior: Behavior learned very early in life.
Conditioned learning: Any behavior with a pleasant result will be
reinforced and repeated; behavior with an unpleasant result is discouraged.
If the outcome depends on pre-existing stimuli, subject will learn to
discriminate on the basis of those stimuli.
"Insight" or "rational" learning (mostly in mammals): Solution occurs
all at once, in a "flash of insight" (or "aha!"). Much learning occurs in
play and exploratory behavior and by imitation.
A classical example was demonstrated among chimpanzees by Wolfgang Kohler. Chimpanzees
were led into a room in which bananas were suspended from the ceiling, high up and
beyond reach. Chimpanzees initially tried jumping up but could not reach them, so they gave up
and began playing with empty boxes that were also in the room. They pushed boxes around, drummed on them
to make noise, climbed on them and jumped off, stuck parts of their bodies into the boxes, picked up the boxes
and threw them, and so on. Suddenly, a chimp would stop all action, glancing here and there (as if figuring
something out). Then, in a "flash of insight" (or an "AHA!" moment), the chimpanzee would carefully place
one box under the bananas, place a second box on top of the first, then climb up and reach the bananas!
Two important characteristics of this behavior are noteworthy:
Importance of exploratory play, in which manipulation of boxes is learned while having fun.
Importance of imitation: a chimpanzee observing this behavior, even through a window, will learn it
and immediately repeat it when given the opportunity.
THUS, raising smart children requires lots of exploratory play, including social play with other children!
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Symbolism and language: Primates can be taught that a stimulus has an arbitrary
meaning (if it stands for something else). The highest form of symbolism
is language.
Learning and intelligence: Intelligence is a capacity for learning
increasingly complex behaviors. It correlates with brain size only if species
of similar size are compared. Mammals are generally the most intelligent
animals. Symbolic behavior and language are keys to human intelligence.
SOCIOBIOLOGY:
- Social behavior is defined as any behavior that influences the future behavior of other individuals
- Advantages of social groups:
- Groups can more easily find food resources (or favorable habitat locations) than isolated individuals.
(This advantage usually increases for larger groups, up to some point.)
NOTE: In most habitats, this advantage is more than enough to compensate for the competition
for food by other group members, but the situation may vary ecologically with the density
and spacial distibution ("patchiness") of the food.
- Groups can more easily detect predators and other risks, and then take evasive or defensive action.
- Finding a mate is easier when you already live in a group.
Altruism: Behavior that risks or diminishes an individual's fitness but increases
the fitness of another individual (usually an offspring or another relative).
- "Inclusive fitness" as an explanation: The evolution of altruism is often explained by the
concept of "inclusive fitness": natural selection favors any behavior that perpetuates your genotype, so a parent who risks
her personal safety to save her offspring is benefitting the genotype that she shares with them. Evidence for this
explanation comes from studies showing that altruistic behavior usually benefits close relatives rather than distant ones,
approximately in proportion to the fraction of the genotype that is shared.
In social species, even altruism to a
genetically unrelated partner ("the father or mother of my children")
can be explained this way because it indirectly increases the long-term fitness of one's offspring.
- "Reciprocal altruism" explanation: altruism between non-relatives is often explained by the hypothesis
that it increases the probability that the individual who benefits will someday return the favor to the benefit of the altruist
("you scratch my back, I'll scratch your back"). Food-sharing behavior is commonly explained this way.
Mating structure:
- monogamy: each adult has one partner of the opposite sex
- polygamy:
- polygyny (common): males have multiple female partners
- polyandry (rare): females have multiple male partners
- promiscuity: each sex has access to multiple sex partners
Parental investment is time and effort devoted to caring for young, feeding them, etc.
- Unequal parental investment (high in females, low in males) tends to favor polygyny and
sexual dimorphism (males and females differ greatly in size and in secondary features like antlers or peacock feathers).
- High parental investment by both sexes favors monogamy and an absence of dimorphism.
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