Monday, Sept. 9 -- Variability in Social Systems & Behavior:
Problems and Methods
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Tinbergen's 4 Questions-- ways to answer the
- The immediate factors that influence behavior
- Development of individual- maturation or learning
- What the behavior contributes to survival or reproduction
- Evolutionary history
Answers are also described as 'proximate' or 'ultimate':
Proximate- In terms of causation
Ultimate- In terms of function
Example: "Why do some birds sing?"
Causation; Change in daylight hours triggers hormonal changes
Development; A "sensitive period" when young enables them to learn songs
from their elders
Function; To defend territory and attract mates
Evolution; Songbirds have the same evolutionary ancestor- others
We'll focus on functional explanations in here.
The Scientific Method
- Formulate hypothesis
- Generate predictions based on hypothesis
- Test predictions through empirical observations
- Either reject or tentatively accept the hypothesis
- Repeat steps 1-5 indefinitely
Three ways to do step 4
1. Controlled experiments; good, but sometimes not possible.
Best to only vary ONE variable at a time. Example; singing and
territoriality. Theory was that singing defends territory. They went out where
birds' territories were established and put up some speakers with territorial song, some speakers with equally loud but meaningless noise. Birds moved right away into the area with just noise, but not as quickly into the areas
with canned song until later.
2. Comparative Method; use correlations between two variables to infer
Mostly developed by Darwin. No one got serious about using it
for social behavior til the 60's when Crook looked at weaver birds. Some
are solitary, some flock. Some nest apart, some together. Some monogamous,
some polygamous. He noticed that they're mostly split into two categories;
||Habitat||Diet||Social Life||Territorial?||Nests||Sex Life
He decided density of food and predation caused the
birds to split up into these two groups. See ch. 2 of book for
Then they tried to apply the same analysis to primates. See
chart in book. It's a little messy. Not all primates fit neatly into the
Best to just try to control for compounding variables.
Another example: Range size of Macaques (fruit-eaters) and Leaf Monkeys
(leaf-eaters). Leaf-eaters have smaller ranges. You might think
fruiteaters have larger ranges since it's harder to find fruit, but this
ignores the fact that bigger animals need more
food so more range. When compared to body-weight, actually leaf-eaters
have larger ranges than fruit-eaters. Doing this type of comparison will
body weight and keep just comparisons between diet.
remember, correlation doesn't mean causation
Another problem you might encounter:
Comparing among species might be misleading since some families have more
branches therefore more data points. So do comparisons among best group;
family, order, genus, etc. Also, figure out what evolutionary ancestry
the animals you are comparing have, and then do the comparisons on the
entire family, ancestors and all. See pg. 36 on how to do this
3. Cost-Benefit Analysis; to study behavioral
that animals make.
Every behavior has costs and
benefits. Uses time, energy, at least. Since animals were designed by
natural selection, you'd expect them to do the thing that has the best
ratio. Gibbons defend territory, orangutans do not. Why does it cost more
for orangs? Maybe 'cause they're slower, have bigger territories, are
To do a proper comparison, you must be able to measure the costs
and benefits. They must be
in the same currency, i.e. hours, deaths, calories
Wednesday, September 11 -- Natural Selection
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The problem: How does one explain the great functionality of so many different species?
The answer: Natural Selection
Definition of natural selection:
Differences in reproductive success that result from heritable differences
Particulate heredity/Mendelian genetics:
Genes do not all blend: some behave as we think today, i.e.
dominant/recessive. When people put together the gene discoveries along
with Darwin's ideas they got it.
3 Types of Natural Selection:
Stabilizing Selection-- The extremes are selected against.
Example: height; mostly beings tend to the average height- not too
many really short ones or really tall ones.
One extreme value is selected for. Example: speed; faster is always
better so a population will tend to get faster over time.
Disruptive selection-- The extremes are both selected for. This
type of selection is not as common as the first two. Example: Prey-type
animal with distinctive markings which the predators know will over time
move away from the norm in both directions.
Micro- vs. Macro- Evolution
micro= Short-term, small changes that we can observe
macro= Big changes over long-term that we can't really observe
Taxonomy is a difficult problem. There are millions of different ways to
classify all the living things on earth. But if we classify according to
evolutionary relations, then there is really only one right way. We may
argue about what is more closely related to what since we don't know what
the right answers are, but there is only one ultimate truth.
A little on sexual selection: (more detail will be forthcoming in a
The catch-phrase shouldn't be survival of the
fittest, but reproduction of the fittest. You only need to survive
long enough to breed. Prolificness is better than longevity: Animals who
live a long time but don't rear many young will be overrun by animals who
live short lives but multiply better. This'll show up in female choice
and male-male competition.
How did such a catch-phrase come about? (No, Darwin didn't invent it- one
of his later proponents did.) "Fitness" in the olden days used to mean how
the organism fit into its environment. Now it just means how well it can
The gene as a unit of selection: Dawkins' 'The Selfish Gene'
Think not of individuals as being selected for, but genes as being
selected for. Individuals don't make exact copies of themselves, but genes
do. So, you may ask, where does altruism come from? How come any mutation
which causes altruism doesn't just get selected right the heck out of
there? Think about it this way: If you sacrifice your life for 1 sibling,
then only half your genes get passed on. This doesn't bode well for your
genes. However, if you sacrifice your life for three siblings, then 1.5
copies of your stuff get passed on so this altruistic gene would survive
better than a selfish gene. This leads to:
Hamilton's equation: Which
determines whether an individual will be altruistic.
In English, Cost should be less than the Benefit times
So if you have an opportunity to sacrifice
yourself for a sibling, who is 1/2 related to you, then you'll sacrifice
only if his benefit is more than twice your cost. (Because altruism genes
who didn't follow this equation wouldn't have gotten passed along as much
as genes who did.)
(Hamilton's is not to be
Common misunderstandings of evolutionary
theory: Group selection: Entire groups do *not* limit their
reproduction for the good of the group. A single mutation would quickly
take over the population. A group can't be selected really, unless it's
completely isolated which is really rare.
Evolution should lead to
perfection: You might think to yourself, "Why after all these years
isn't everything perfect? Take primates with a prehensile tail; wouldn't
it be better to just have some more arms? How come evolution hasn't made
arms?" The problem is, that particular variation wasn't present in the
population to work with- only genes which are present can be selected and
Another example: smarter is better, right? So how come all
animals aren't so smart? Well actually brains use a lot of fuel and lots
of animals don't even need 'em.
Evolution is striving for a specific
goal: Good evolutionists don't use the terms 'higher' and 'lower.'
Certain organisms are not inherently better than others. Other organisms
are not sitting around in primordial soups trying to evolve into humans.
|And here, by the
special request of my grandfather, is the paper I wrote on natural
selection for this class. |
Friday, Sept. 13 --
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New Office Hours:
Monday 1-3, not 2-4
Today we're going to be looking specifically
at primates, not at behavioral theories or terminologies.
Describe physical characteristics of
Describe general features of behavior
Question we're going to answer today:
What makes a primate?
|How do we come up
with a definition of the order primates? It is difficult because there's
quite a range of differences in characteristics. For instance, there is a
two-to-three-thousand-fold size difference between largest and smallest
Primate Anatomy A
definition from 1873, written by St. George Mivart:
"Unguiculate, claviculate, placental mammals, with
orbits encircled by bone; three kinds
of teeth, at least at one time of life; brains
always with a posterior lobe and calcarine fissure; the innermost digits
of at least one pair of extremities opposable, hallux with a flat nail or
none; a well-developed caecum; penis pendulous;
testes scrotal; always two pectoral mammae."
A link to
the Oxford English
Dictionary (Available only to UM-affiliated users, sorry)
Seriously though, they're not very physically specialized. Not when
compared to say a giraffe or a platypus! There are some defining
are very visual. Compared to other mammals, the eyes have moved more to
the forepart of the head. This gives good binocular vision.
Teeth: Incisors, canines, and molars. (The
three kinds referred to in the definition.) Diversity of tooth types is
because of diversity in diet. The canine teeth rip food and get it into
mouth, while molars grind the food to prepare it for digestion. Felines,
who have a less-varied diet, have less varied teeth.
Brain: A lot of development in the neo-cortex which
implies heavier reliance on learning and memory. Also, olfactory bulb is
rather reduced, especially in the ones with bigger neo-cortex. Older
primates, like the prosimians, have a larger olfactory bulb but a smaller
neo-cortex. More recent developments have a smaller olfactory bulb and
Fairly generalized so
it can be used for many different modes of locomotion. Skeletal
proportions have great variation among species, mostly related to
Ecology and Behavior
Worldwide geographic distribution: Primates are fairly widely
distributed; on 5 out of the 7 continents (Not Australia or Antarctica.)
They're more restricted now than before, mostly due to climate changes-
they're basically a tropical order. Mostly they're found in the rain
forests of SE Asia, west-central Africa, and South America. Exceptions:
Barberry Macaque in N Africa, Japanese Macaque in Japan, and some
Habitat types: These differences in
habitat are caused by differences in rainfall, going from highest to
Primary forest: Tall trees with a dense, multi-level
Secondary forest: Spots where primary forest has been
disturbed so it doesn't have tallest trees- more dense understory due to
more light getting in.
Gallery forest: Develops along
waterways in drier areas.
Woodland: Trees are sparser and
shorter, with more shrubbery.
Savannah: Made up of grass and
scattered trees (pretty dry here).
Within any given habitat, there are
Microhabitats: These are smaller divisions
within the same habitat: You might have altitudinal gradience where two
species live in the same habitat but at different altitudes. Also, within
a forest, they might use different levels of the canopy: Highest is the
emergent trees (up to 300ft tall) that poke out above canopy. Next comes
the main canopy, which has a lot more horizontal branches and vines and
things. The main story comes next, with more trunks and vines, and finally
we find the ground. Certain species may specialize in one particular
height level, rarely venturing out of it. (This type of microhabitat is
also known as vertical distribution)
Patterns Most mammals are nocturnal: they sleep during the day.
Primates on the other hand are mostly diurnal. The holdouts are the
prosimians (the less-developed primates who also have smaller
neo-cortexes.) All apes are diurnal. All monkeys except the 'night monkey'
are diurnal. Some monkeys could be called crepuscular maybe, but not
Primates, being 'unguiculate,' not only have nails or claws, but usually
flat nails instead of claws. This is because hands and feet have become
modified for grasping.The exception is the prosimians; they still have
The Classifications a.k.a Different ways to
Quadrapedalism; May be arboreal(african
monkeys) or terrestrial (macaques and baboons). A specialized
form called knucklewalking is seen in african apes, gorillas, chimps, and
Leaping; Seen in squirrel monkeys. Vertical
leaping from a clinging position on a trunk is seen in the prosimians such
as the tarsiers and indries (who still have claws).
Suspensory climbing; Hanging down from hands from branches.
Orangutans do this. Gibbons do a special type of suspensory travel; they
Bipedalism: Examples are us; also
chimps and spider monkeys do it. Mostly they bipdedal (if that's a word)
for shorter distances or when carrying something, but don't use it as
their primary mode of movement.
'...well-developed caecum...' This is a sac
in the digestive system which comes off at the top of the large intestine
but leads nowhere. Its harbors bacteria used in the digestion of some
nutrients that we can't break down, such as cellulose or complex
carbohydrates. Bacteria in the caecum digests this stuff for us.
Gross dietary categories
frugivore fruit-eater: orangutans
folivore leaf eater: leaf-eating monkeys
insectivore insect eater: tarsiers
gummivore gum eater (saps and gums from injuries to trees): tamarins and marmosets
omnivore animal & plant eater
faunivore animal eater (includes insectivores) but this category also includes invertebrate-eaters
herbivore plant eater (includes leaf and fruit eaters)
*Note if we say an animal is one of these types it doesn't mean that's all they eat! Some animals have stricter diets than others.
Spacing systems-- Nomadic-migratory vs. Philopatry
Many animals move around quite a bit. Primates don't move so much. They
are called philopatric which means they stay in the same place. This is
‘cause they live in such a complex environment; they need to know where to
find food, sleeping areas, and predators. Therefore they stick around
within an area that they know. Maybe an animal will move to another
territory once when it reaches adulthood, but that's usually it.
How far they go in one day; day range (often measured in length)
How far they go in a longer period of time (like a year); home
The area in home range which is used most; core area (area)
If they actively defend their home range, then it's called a
territory and if they don't, then it's just called a home range.
Examples: Gibbons have territory and they defend it. They move pretty
quickly, so their day rage is pretty long, but their territory is
relatively small since they do defend it. The orangutan moves more slowly
so its day range is shorter. Its home range, not being a territory, is
pretty big, however. When undefended, home ranges often overlap quite a bit.
Social Groups: Solitary vs. Gregarious
Mostly, primates are social animals. Most mammals aren't. Holdouts, as
usual, are the prosimians many of whom are solitary. Monkeys and apes are
almost all in groups, the prototypical example being baboons who live in
huge groups. An exception is the orangutan who is a solitary beast.
A Classification of Social Group Types
Note that these often correspond to mating system classifications.
Noyau: Animals have overlapping home ranges, and the sexes don't
live together. There's no territoriality. Each female has a home range
while males have larger home ranges that cover several female ranges. This
is the system seen in orangutans. Usually goes with a promiscuous mating
Monogamy: One territory for each pair and their offspring.
An example is the gibbons. Goes hand-in-hand with the monogamous mating
Polyandry: Each territory has one female and many males.
Guess which mating system they use.
Multi-male group: (Should really be called multi-male,
multi-female group, since each territory has many of both sexes.) Macaques
are an example. Usually a promiscuous mating system.
One-male group: Such as the leaf-monkey. Usually a
polygynous mating system. The leftover males form bachelor herds who raid
periodically to take power and women from aging reigning males.
Fission-fusion society: This type is less common, but can be
seen in chimps, bonobos, and spider monkeys. A group has shared territory.
All the members are friendly to each other and work to keep non-group
members out, but they don't travel toge ther as a group. They have smaller
subgroups that join and split almost constantly.
Hamadryas baboons: This category is used almost just to
describe their systems, so they got the naming of it. It is a complex
hierarchical system, with several levels. The basic unit is a one-male
unit, with accompanying females, but the units co mbine into larger groups
called clans. These are made up of related males' groups who merge for a
while to forage and socialize, but don't share women. Clans will sometimes
merge to form troops who share common sleeping sites, often on cliffsides.
Sometimes a troop will move as unit to a new location, but usually during
the day they split into clans. A similar system is seens in the golden
monkey and proboscis monkey, but it hasn't been so well described.
Monday; film will begin right at 11 since it's exactly 60
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First meeting: We received the section syllabus and introduced ourselves.
Then we discussed four different primates: The orangutan, leaf-eaters,
macaques, and gibbons. We compared their social structure, diet, and
territoriality, discussing which factors influenced the differences.
Let me know your thoughts: firstname.lastname@example.org
Last modified: Saturday, September 14, 1996