Biology Chapter 9 Notes: Evolution and Biology
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Clear and consistent preference for sweet and fatty foods; animals have taste preferences
because they cannot create their own food
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Will examine cooperation, conflict, communication, mating and parenting; the evolution
Behaviour: encompasses any and all of the actions performed by an organism, often in response to its
environment or to the actions of another organism, warblers singing; feeding is one of many behaviours
influenced by natural selection; mutated genes that reduce child care does not increase in population
Innate Behaviours (instincts): does not require any environmental input to develop; present in all
individuals in a population; do not vary much from one individual to another or over the lifespan of the
individual; fixed action pattern and triggered under certain conditions; requires no learning and runs to
completion; egg-retrieval in geese (egg shaped objects that are bigger), aggressive displays and attacks
by stickleback fish (in response to red colour)
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Some behaviours require a degree of learning; rhesus monkeys are afraid of snakes and even
the site of snakes will engage monkeys in fear related responses; captive monkeys will view
another monkey expressing fear towards snakes in real life or on video and then express fear
towards snakes
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Behaviours learned easily and by nearly all individuals are called prepared learning; language is a
dramatic example; underscores the fact that organisms don't learn everything with equal ease;
well prepared to learn behaviours that have been important to ancestors and reproductive
success; takes time to adjust to modern society
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Natural selection produces organisms that exhibit relatively simple behaviours in response to
certain situations or environmental conditions
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Pleasure from sex has the incentive to seek out additional opportunities to experience that
pleasure; behaviours that lead to a specific outcome that increases the animal's relative
reproductive success will be favoured by natural selection; this can trick animals sometimes (egg
retrieval by geese); avoiding incest among humans like kibbutzim in Israel
Kindness & Altruism
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Altruistic behaviours: behaviour that come at a cost to the individual performing them while
benefiting a recipient; seems that way in the animal world; must define costs and benefits in
terms of their contribution to an individual's fitness
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Puzzled Darwin because natural selection typically supported selfish behaviour instead of
altruistic-appearing behaviours (social spider giving birth to spiderlings)
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Virtually all of apparent acts of altruism in the animal kingdom prove to be not truly altruistic;
have evolved as a consequence of either kin selection or reciprocal altruism
Kin Selection: kindness toward close relatives; lead to the evolution of apparently altruistic behaviour
toward close relatives; with a potential K allele, it can increase the behaviour in a way that increases
fitness of a close relative of yours while decreasing your own fitness; thus, an increase market share of
allele K; increases the fitness of the relatives you help might compensate for own reduced fitness
because allele K will, overall, increase its frequency in the population when helping relatives increase
their reproductive output
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ground squirrels are prey to birds; some squirrels see the predators and make alarm calls while
other squirrels keep their mouth shut
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80% of squirrels making alarm calls are female and usually older females
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increases relative's fitness; likely it was that the alleles being propagated by the recipient of the
altruistic-like behaviour were the same alleles found in the altruistic individual; benefits to
relatives are greater than the personal cost
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the more closely related, the stronger the chance of kin altruism
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in an unrelated colony, the older female would still be as likely to make a call; programmed
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dividing wealth to relatives are another example; 46% to children, 37% to spouses
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individual's fitness is not just measured by his or her total reproductive output (direct fitness);
also includes the reproductive output that individuals bring about through their seemingly
altruistic behaviours towards their close kin (indirect fitness)
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Inclusive fitness: sum of an individual's indirect and direct fitness
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since no two individuals are identical there will be conflict (women and fetuses); at some point,
it is in the mother's best interest to reduce the amount of glucose and other nutrients given to
the fetus; step-parents vs. biological parents abuse to preschool children
Reciprocal & Apparent Altruism: can lead to evolution of apparently altruistic behaviour towards
unrelated individuals; the carrier of a allele R causes you to help unrelated individuals and allele R might
still increase its market share and the individual might be more likely to return the favour
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vampire bats may vomit up a blood meal for an unrelated individual; bats only do this for
individuals that will return the favour or have previously done so; their own survival is improved
in the long run and the behaviour is favoured by natural selection
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the acts that seem altruism may be selfish in actuality
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both individuals in reciprocal altruism give up something of relatively low value in exchange for
getting something of great value at a later time when they need it
Reciprocal altruism can evolve if certain conditions are met:
1. Repeated interactions among individuals, with opportunities to be both the donor and the
recipient of altruistic-appearing acts
2. Benefits to the recipient that are significantly greater than the costs to the donor
3. The ability to recognize and punish cheaters, individuals that are recipients of altruisticappearing acts but do not return the favour
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selfishness is expected to be the norm among unrelated individuals; conditions for evolution of
reciprocal altruism are not satisfied in many species and that may cause it to be rare but with
exceptions; smaller fish may be allowed to swim into the mouth of a larger fish and clean
parasites by eating them; you scratch my back and I'll scratch yours
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reciprocal altruism is very common among humans; interactions and relationships
Behaviours and Natural Selection
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natural selection can lead to fitness-reducing behaviours; fitness not only is an individual's
reproductive success but also depends on the specific environment in which the organism lives;
certain behaviours have been favoured by natural selection over others
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adaptation to a new environment takes time and the more quickly an environment changes, the
more likely it is that the evolved behaviours of a population will no longer be appropriate
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Selfish genes win out over group selection; behaviours that reduce an individual's reproductive
output are not likely to evolve; natural selection favours individuals producing more offspring
relative to those producing fewer offspring
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the selfish offspring will pass on the selfish allele at a higher rate than the alternative allele is
passed and reproduce more
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group selection: describes the evolution of a trait that is beneficial for the species ore
population while decreasing the fitness of the individual exhibiting the trait; almost never seen
in nature
Sexual Conflict
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there are big difference in how much males and females must invest in reproduction; males and
females hinges on a physical difference between the sexes; female is defined as the sex that
produces the larger gamete
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Reproductive investment: material and energetic contribution to the offspring; energy
expended in the growth, feeding and care of the offspring
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the number of offspring a male can produce increases with the more females the males find;
additional mating result to additional offspring; this does not work for females
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internal fertilization in most mammals takes place in females
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lactation occurs in females and not in most males; nuturing during both pregnancy and lactation
can only be accomplished by the female; early investment in reproduction is much greater for
females than males;
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investments may become more equally divided after fertilization; birds after fertilizing the eggs;
males and females can protect and incubate the developing embryo and both parents can feed
the chicks;; kittiwake male gulls usually produce 26 and females product 28
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males cannot be 100% certain that any offspring the female produces are his progeny; paternity
uncertainty
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Males and females are vulnerable at different stages of the reproductive exchange; gender roles
with regard to sexual willingness are greatly influenced by socialization and can vary crossculturally; humans like nearly all mammals are characterized by greater initial reproductive
investment by females; the sex with the greater energetic investment in reproduction will be
more discriminating when it comes to mating; members of the sex with less energetic
investment in reproduction will compete among themselves for access to the higher-investing
sex; bush cricket males lose 25% of body weight when mating and therefore, is highly selective
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greatest vulnerability for males comes when they provide paternal care to offspring; male may
be investing in offspring that are not his own
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there is tremendous variability among different species in male and female behaviours; DNA
fingerprinting to identify the parents of bird offspring has lead to some surprising results; more
cases of offspring having different fathers than observers believed; can supply meaningful
insights into morality or ethical decision making
Mating Tactics
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tremendous variation in the relative investment in reproduction among males versus females;
males generally increase their reproductive success by mating with many females and have
evolved to compete among themselves to get the opportunity to mate; females increase their
reproductive success by caring for their offspring and being choosy about selecting a mate;
choosiness increases the likelihood that a female will select only those males that have plentiful
resources or relatively high-quality genes;
Choosiness is manifested by four general rules:
1. Mate only after subjecting a male to courtship rituals; many bird species require the male to
perform an elaborate and time consuming courtship dance before the female will mate with the
male; can generally be counted on to stick around to see a brood through hatching and early
care if committed to this ritual
2. Mate only with a male who controls valuable resources: territorial defense; reproductive
success increased if the territory is rich in resources
3. Mate only with a male who contributes a large parental investment up front: commit resources
to future offsprings; nuptial gift as a part of a courtship behaviour; male might take back gift
after mating to attract other females
4. Mate only with a male that has a valuable physical attribute: male contests determine the
dominance rankings of males; may be based on some physical attributes or correlated with
health; females generally do not have to advertise their health because of investments or social
complexities
Mate Guarding:
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to minimize paternity uncertainty, males may choose to leave after mating for other females;
may not be the best strategy of non of the potential offsprings survive so there may be an
incentive for males to provide some parental care regardless of uncertainty
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mate guarding: can reduce the males vulnerability (of consequence and attempt to reduce
paternity uncertainty); has a danger zone in the period it takes the female to be fertile; male
would sometimes not separate from female for an hour or a day (until the female is sure to be
fertilized); black widow males breaks off sexual organ so the females cannot mate again and
allows the females to eat the male for resources
Monogamy versus Polygamy
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the biggest male elephant seals that dominates the land fathered 85% of the offspring;
polygamy is exmplified by elephant seals; polygamous mating can be divided into polygyny and
polyandry
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polygyny: invidiaul males mate with multiple females
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polyandry: females mate with multiple males
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monogamy: individuals mate and remain with just one other individual
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monogamy and polygamy are two different types of mating systems
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peacock tails with under 140 eyespots usually gets no mates while 160 eyespots get six or more
mates; all females are able to attract a mate regardless of wheather they are the most fit
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differences between animal mating and their bonding behaviour and difficulties describing
systems; males and females form a pair bond; spend a high proportion of their time together
sharing a nest or home and contributing equally to parental care of offspring which is
monogamy; male and female may be mating with other individuals in the population while in a
pair bond and it is described as polygamy
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another difficulty lies because the mating system may vary within the species; some individuals
may be monogamous while others are polygamous; systems may even change over the course
of an individual's life
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males and females often differ in their mating behaviour; there will be a variety of species with
each type of mating system and difficult to generalize
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among 10,000 species of birds, 90% of them appear to be monogamous
Sexual dimorphism & Behaviours
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when the sexes of a species differ in size or appearance
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smaller males have relatively low reproductive success; no selection for larger body size among
female elephant seals because females of any size can mate; dramatic size differences between
sizes in certain species
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one parent invests more in caring for the offspring; mating system tends toward polygamy; one
sex (usually females) is choosier; one sex (usually males) competes
Behaviours of Sexual Monomorphism
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both sexes usually look similar and have same sizes
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both parents invest (approximately) equally in caring for the offspring; mating system tends
toward monogamy; both sexes are equally choosy when selecting a mate
Animal Communication and Language Abilities Evolve
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not all animals need to talk to communicate; moths can release chemicals as a ready to mate
signal
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Communication: an action or signal on the part of one organism that alters the behaviour of
another; huge range of behaviours require communication; defending territory, alerting
individuals, announcing one's readiness for mating, establishing one's position in a dominance
hierarchy, caring for offspring
1. Chemical communication: molecules released by an individual into the environment that trigger
behavioural responses in other individuals are called pheromones; airborne mate attractant of
silkworm moth, territory markers such as dog urine, chemicals that influence length of
menstrual cycle in women
2. Acoustical: sounds that trigger behavioural responses are abundant in the natural world
3. Visual: displaying visual signals of threat, dominance or health and vigor; dances like the
honeybee waggle dance when a honeybee scout returns to the hive after successfully locating a
source of food; the bees that observe the dance are able to leave the hive and quickly locate the
food source
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language is a very specific type of communication in which arbitrary symbols represent concepts
and a system of rules (grammar) dictates the way the symbols can be manipulated to
communicate and express ideas; can be difficult to identify language and can differ under
certain situations
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evolution of language influences many of the other behaviours as well; reciprocal altruism may
be influenced as language makes it easier for individuals to convey both their needs; courtship
and maintenance of reproductive relationships may bring resource and value in the interaction
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Honest signals reduce deception: a signal that cannot be faked and that is given when both the
individual making the signal and the individual responding to it have the same interests; carries
the most accurate information; certain calls cannot be faked or replicated by others; when an
animal can increase its fitness by deceiving another, the deception can also be expected to
evolve; chicks can exaggerate its need for food leading to faster growth and better health for
that individual
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an organism's phenotype is not limited to its physical traits but includes the organism's
behaviours as well; behaviours respond to selective pressures and evolve