By Jennifer de Puzo, Kathryn
Marshall and Maribel Pulido
Females of various species have evolved to fight
each other. However, unlike males, they rarely fight, and when they do, they do
not fight to kill each other. More often, these fights are more verbal than
physical. Females also usually do not fight over males, but over more
significant matters. For example, birds will fight over nests. These fights are
to assure their genes get passed onto the next generation and are more over
resources for their offspring, rather than over males to copulate with.
Females have evolved to resort to various
manipulative strategies. One way females do this is by manipulating other
females. For example, in some species of newts, the females will steal male
sperm packets left for another female. Female African butterflies will often
chase away any other females they see near their mate. Another way females are
manipulative is that they will intervene during another couple while they are
copulating or courting. For example, some toads need males to watch their eggs
for them, so in order to steal another female’s mate; she will intervene in the
mating process. An additional method females will use is to manipulate males to
make him invest more in her and her offspring. One example of this is some male
frogs must hold the eggs in his vocal sacs for a period of about 52 days. He
must do this in order for his offspring to survive. But during this period, he
is unable to sing to attract more females.
Females may also use preventative strategies to keep
her mate with her and her offspring. She wants to get as much of an investment
from him as possible. If her mate copulates with another female, he may leave
her offspring to help raise the offspring of the second female. One way she
tries to prevent her mate from courting another female is to intervene. For
example, male burying beetles will stand on their heads to attract other
females with a scent that comes from their abdomens. If he already has a mate,
and she sees him doing this, she will knock him over so he cannot attract other
females. Another example is female pied flycatchers that will interrupt her
male if she sees him singing to another female. Another
method females may use to prevent her mate from investing time in
another female and her offspring is infanticide. If more than one female mates
with the same male, they will often try to kill each other’s offspring. One
species that is an example of this are house sparrows. If a male has more than
one mate, he will only help the female whose eggs hatch first. So the second
female will try to kill the first female’s eggs.
Females may also use a more passive strategy to keep
her mate. A passive strategy that some females use is when her mate is trying
to court another female, instead of getting angry, she may instead use the
opportunity to copulate with him again. His courting and act will actually
arouse her as if it is meant for her, instead of trying to stop him. One
species that does this are starlings. However, if this doesn’t work, and she sees
that another female is attracted to her mate, she will use more aggressive
actions. For example, northern harriers will intimidate and possibly attack a
rival female. Blue tits will knock their rivals out of the air. Starlings will
sing at another female to scare her off or if she sees her mate looking at
another nest hole, she will fill it up to make it look
occupied.
Females will at times fight with other females over
males. They have evolved to fight for three reasons. First, they will fight out
of desperation if there is a lack of males. Second, they will fight out of
aspiration. This is when females are choosy with who they mate with and they
strive to mate with the superior males. Third, they will fight out of
possessiveness. This is to keep her mate from taking a mistress, and to keep
him from investing in another female’s offspring.
This chapter starts off with a
question: can animals put a “spell” on other animals in order to have them fall
in “love” with another animal. Though there are no real “spells” per se, there
are forms in which animals can stop another animal from copulating with another
animal. Women normally benefit from having one partner because if they have
more that one, problems arise, such as male-male conflict. They can engage in
physical violence, use “chemicals to disable his predecessor’s sperm, or he can
even make is own sperm hard to remove.” These are ways that they try decrease
the male competition for the females.
Male-female conflict also exits.
Males find ways to gain control of the women so that she will not have other
males to copulate with. Males can “deliver drugs that switch off her sex
drive-an invisible, chemical chastity belt. Or daub her with an
“antiaphrodisiac,” a chemical that makes her stink, so that other makes will
find her repulsive.”
Male Australian field crickets, the
common housefly, fruit fly, and garden snails all use sneaky strategies in
making it difficult for other males to copulate with their “female.” Seminal
fluid alters a female’s behavior. It can turn off a women’s sex drive, some
males can make it difficult to remove in females, and in some cases it can
induce aggression in women towards other males. Therefore, males have powerful
effects on females. The
Though there are some cases, like in
the
Finding a “partner” to engage in
copulation and to have offspring becomes a difficult task for certain species
despite the fact that the super male characteristic exists. The most important
thing to do it to find a way to fertilize the egg by having a sperm attach to
it. Reproduction is the most important concept in any species: “a group of
organisms that can interbreed.” It is through interbreeding that new species
can form. A see urchin is an example of how certain species can create new
species. Male see urchins produce different types of proteins that eggs have
similarities for. These proteins are
producing different types at an incredible rapid rate and consequently, new
species are being produced.
The “battle of the sexes” is one
reason why reproduction evolves so fast.
This statement can only be proven if “rapid evolution in a given male
reproduction protein is fueling the rapid evolution of a given female
reproductive protein, and vice versa.” However, it does turn out that male
protein is evolving in response to the egg. This occurs by having the male’s
protein repeat itself twenty-eight times. However, repetitions of a protein can
also lead to genetic problems. Huntington’s disease is an example of how
changes in the number of repeats can cause problems in humans. “ When a repeated unit is large, a mutation that occurs in
one unit may spread gradually through the other units through a passive process
known as concerted evolution.” Though repetition of some protein can cause
problems, in some species the mutation is and advantage to those who can only
recognize its rapid change.
Homosexuality is common among
species like the bonobos, penguins, and dolphins. Many people question their
behaviors and motives. Some people think that it enables them to achieve and
orgasm, as it is found to be true for the Asian monkeys, it serves as a social
function, facilitates teamwork, it is an antisocial function, or it is an act
of desperation. Homosexuality does not coincide with the evolutionary theory of
reproducing to keep the genes going through the generations. However there are
some homosexual species, such as in the gull, where reproduction is possible.
What about the species in which reproduction is possible? What function does it
serve if they cannot produce offspring?
Homosexuality becomes difficult to
explain only if it has a genetic component, is exclusive, or it makes up a
significant proportion of the populations. Though the search for homosexual
genes has not been conclusive it seems likely that sexual orientation among
mammals will turn out to have some genetic basis. It has also been difficult
for researchers to find if homosexuality is exclusive throughout a species
life. They also find it difficult to measure if and how animals have been
exclusively homosexual throughout their lives.
The traditional explanation for
homosexuality explains that genes can be maintained if homosexual individuals
act to increase the reproductive success of their relations. However, “there is
not evidence that homosexuality amounts to an indirect way of spreading genes;
in species of birds and mammals where young animals help their parents raise
the next brood.” Current explanations
for homosexuality believe that it evolved as a reproductive suppression
however, not evidence can explains homosexual behavior. It has also been
discussed that homosexuality could be maintained if the genes were favored by
natural selection. This could happen by heterozygote advantage where an
offspring would have two forms of one gene rather than one form of gene from
each of the parents. Humans who have two copies of the same form are an average
heterosexual, but sterile. If you were a person where you would have one form
of each would mean that that person would be a highly fertile heterosexual.
True monogamy is so rare that it is one of the most deviant behaviors in biology. Before the 1980s, over 90 percent of bird species were believed to be monogamous at least for the duration of the breeding season, and many couples were thought to mate for life. However, better genetic techniques and the spread of paternity testing proved this idea false. If animals live in pairs, they are said to be socially monogamous, which is a term that does not make assumptions regarding their sex lives.
Monogamy will evolve as a strategy
for all members of a population only when it is in the best interest of both
males and females. This means that
monogamy will last when the amount of surviving children of monogamous couples
exceeds those of polygamous couples.
Since fidelity is rarely in the best interest of one of the parties, let
alone both parties, it is a rarity.
There are several theories of
monogamy that are discussed in this chapter.
The first is the Good Wife Theory of Monogamy. This essentially states that males’
opportunities to philander are lessened because females are obsessively
faithful to her mate for fear of losing his help with the kids. According to the Good Wife Theory of
Monogamy, monogamy is a female plot forced on males.
This theory is unlikely to apply because of three
reasons. First, the assumption that
males would wander if they could and that being unfaithful is in his interest
is often wrong because sexual fidelity can be in the male’s interest. Second, monogamy can evolve even if the male
does not help the female raise the children.
The third issue with the Good Wife Theory is that a female’s need for
male help does not necessarily guarantee her fidelity. For example, fat-tailed dwarf lemur male/female
couples live together in pairs and the females cannot raise offspring on their
own. Still, genetic testing shows that
infidelity is widespread and that males oftentimes
help to raise children that are not theirs.
When fidelity and cooperation go together, monogamy is typically not the
consequence as the Good Wife Theory states; rather monogamy is the cause of
fidelity and cooperation.
Other theories of monogamy are the Danger Theory of
Monogamy and the Pop-‘Em-Out Theory of Monogamy. If females are spread out then males might
find that they are better off staying with a single female
and keeping rivals away. It might
be risky to leave because finding another female would involve a dangerous or
long journey. There is a direct
relationship between the risk and the incentive to remain. The greater the risk to leave the female,
then the greater the incentive is for the males to remain with their
females. This is the Danger Theory of
Monogamy. The Pop-‘Em-Out Theory of
Monogamy deals with the time between a female’s breeding. If the female breeds quickly, then there may
be no point for a male to leave on a journey to find another female. The Lysiosquilla sulcata are mantis shrimp
that have strong circumstantial evidence for monogamy.
If a female gains significantly from having a male
around, then she may be less likely to throw him out. For example, a male could help a female
defend her territory or he could help her with childcare.
The male Djungarian hamster is “such attentive as a
father that he plays with midwife for the births of his pups (the only male
mammal so far known to do this as a matter of routine), helping them to emerge
from the birth canal, opening their airways so they can breathe and licking
them clean…Consistent with the Pop-‘Em-Out Theory, female Djungarian hamsters
live apart from one another: their ranges do not overlap. And they are prolific breeders. In a year they can produce eighteen litters
of between one and nine pups each. In
contrast, their close relative the Siberian hamster breeds for only a few
months of the year and exhibits neither paternal care nor monogamy” (156-7).
Monogamous organisms are often aggressive toward any
animal that’s not their
partner. It’s usually thought that they
are aggressive because they are monogamous.
Sometimes they may be monogamous because they are aggressive. If aggressive individuals toward members of
their own sex have more surviving offspring than more amiable creatures, then
monogamy may arise as a side effect of that aggression. This is known as the Sociopath Theory of
Monogamy.
Monogamy
may arise when cheating or desertion by either partner results in total
reproductive failure for both. This is
the Mutually Assured Destruction Theory of Monogamy or
“When a boy prairie vole meets a girl prairie vole and they decide to become an item, they consummate their relationship by copulating anywhere from fifteen to thirty times in a twenty-four hours. From this point on, the lovers grow greatly attached, endlessly cuddling and grooming each other, the picture of mushy affection…. Before losing his virginity, a male is a peaceful sort of chaps…after his first night of passion his personality changes. How if he sees any prairie vole- male or female- who is not his partner, he’ll attack vigorously. For a male prairie vole, the sex act causes the release of vasopressin, a hormone that bins to special receptors (160).”
Since monogamy has evolved independently in different species, the mechanisms may well differ from one monogamous species to the next. If sex also turns out to have potent hormonal effects in other monogamous species, this would explain why many of them regularly engage in sex that, owing to its timing, cannot possibly result in reproduction. It is important to remember that understanding the genetic mechanisms of monogamy is quite separate from understanding why organisms have evolved to be monogamous in the first place.
Humans cannot be described as exclusively monogamous. Some individuals are faithful to one partner for their whole wives; few have or admit to having thousands of sex partners. In monogamous species, males and females tend to be roughly the same size; in species where a few big males hold harems, males tend to be enormously bigger than females. Human males tend to be only slightly larger than females. In the gorilla, adult males are typically twice the weight of adult females.
In respect to physical difference between human males and other male apes, testicle size is usually associated with the risk of sperm competition. “Males that are at low risk of sperm competition generally have testicles that are small in relation to their body size. Males that are at high risk of sperm competition generally have enormous testicles in relation to their body size. Male gorillas are at a low risk of sperm competition and have tiny testicles. Male chimpanzees are at high risk of sperm competition and have gigantic testicles. In comparison, human males have medium-sized testicles, suggesting a low to moderate risk of sperm competition” (163).
The rate of infidelity as measured by genetic paternity testing is rumored to be extremely high among humans-30 percent or more. These results need to be treated with more caution in humans than in other species: contraception and abortion enable humans to avoid having a child during an extramarital affair.
“For most boys and girls, wedding rings are made of fool’s gold- real, true love is precious and rare, the confluence of bizarre biological forces. Several factors may contribute to monogamy, but you’ll find that true love works best when it is absolutely MAD” (165).
I.
Females of various species fight, just like the males do.
A.
Rarely do females fight, and when they do,
they do not fight to kill each other
B.
Mainly will fight when males are in short
supply
C.
Females will often resort to various
manipulative actions
1.
Females may manipulate other
females
2.
Females may, for example,
intervene during copulation
3.
Females may manipulate males
by making them invest more time into her and her offspring
D.
Females may also take
preventative actions to keep her mate
1.
Females may intervene in her
mate courting another female
2.
Females may prevent her mate
from investing time in another female and her offspring
a)
Infanticide
E.
Females may use a more passive strategy to
keep her mate
1.
For example, when her mate
is trying to court another female, instead of getting angry, she may instead
use the opportunity to copulate with him again
II.
Females have evolved to fight over males for these reasons
A.
Desperation -lack of males
B.
Aspiration - she chooses to mate with superior males
C.
Possessiveness - to keep her mate from taking a mistress
I. Monogamy
A.
Monogamy will evolve as a
strategy for all members of a population only when it is in the best interest
of both males and females
B.
Monogamy will last when the
amount of surviving children of monogamous couples exceeds those of polygamous
couples
III.
Theories of Monogamy
A.
Good Wife Theory of Monogamy
1.
Males’ opportunities to philander are lessened
2.
Females obsessively faithful so mate can help
raise offspring
3.
Unlikely to apply for three reasons
a)
The assumption that males
would wander if they could and that being unfaithful is in his interest is
often wrong because sexual fidelity can be in the male’s interest
b)
Monogamy can occur even if
male does not help raise children
c)
Female’s need for male help
does not guarantee her fidelity
B.
Danger Theory of Monogamy
1.
Males might find that they
are better off staying with a single female and keeping rivals away
2.
Might be risky to leave
because finding another female would involve a dangerous or long journey
C.
Pop-‘Em-Out Theory of
Monogamy
1.
Deals with the time between
a female’s breeding
2.
If the female breeds
quickly, then there may be no point for a male to leave on a journey to find
another female
D.
Sociopath Theory of Monogamy
1.
Monogamous organisms often
aggressive toward any animal that is not their partner
2.
Usually thought that they
are aggressive because they are monogamous
3.
If aggressive individuals
have more surviving offspring than more amiable creatures, then monogamy may
arise as a side effect of that aggression
E.
Mutually Assured Destruction Theory of
Monogamy (“MAD”)
1.
Cheating or desertion by
either partner results in total reproductive failure for both
III.
Physical Characteristics Related to
Monogamy
A.
In monogamous species, males and females tend
to be roughly the same size
B.
Human males tend to be only slightly larger
than females
C.
Testicle size usually associated with the risk
of sperm competition
a.
Males at low risk of sperm
competition generally have small testicles
b.
Males at high risk of sperm
competition generally have large testicles
c.
Human males have
medium-sized testicles, suggesting a low to moderate risk of sperm competition
Chapter
8 Critical Review Items:
(a)
The main point in Chapter 8
is that females will often take preventative measures in order to keep her mate
with her to get the most investment out of him that she can. For example, she
may fight off other females to keep the females away from her mate, or she may
prevent him from flirting with other females. An interesting point is that at
times, instead of being angry with her mate for courting other females, she
will take the opportunity to copulate with him again.
(b) One weakness of this chapter
was the organization of it. It did not seem to be organized at all. Instead it
jumped from topic to topic and mixed topics together.
Chapter
9 Critical Review Items:
(a)
There are some homosexual species that can in fact have offspring, usually
females.
(b) The chapter needs more
clarification and explanation on the heterozygote advantage.
Chapter
10 Critical Review Items:
(a) An interesting point in Chapter 10 is the Danger Theory of Monogamy. If females are spread out then males might find that they are better off staying with a single female and keeping rivals away. It might be risky to leave because finding another female would involve a dangerous or long journey. There is a direct relationship between the risk and the incentive to remain.
(b)
This chapter is not direct enough and is extremely confusing and hard to
follow.
I.
Females of various species fight, just like the males do.
A.
Rarely do females fight, and when they do, they do not fight to kill
each other.
B.
Mainly will fight when males are in short supply.
C.
Females will often resort to various manipulative actions.
4.
Females may manipulate other
females.
5.
Females may, for example,
intervene during copulation.
6.
Females may manipulate males
by making them invest more time into her and her offspring.
D.
Females may also take preventative actions to keep her mate.
1.
Females may intervene in her
mate courting another female.
2.
Females may prevent her mate
from investing time in another female and her
offspring. For example, infanticide.
E.
Females may use a more passive strategy to keep her mate.
1.
For example, when her mate
is trying to court another female, instead of getting angry, she may instead
use the opportunity to copulate with him again.
II.
Females have evolved to fight over males for these reasons:
D.
Desperation. When there is a lack of males.
E.
Aspiration. When she chooses to mate with superior males.
F.
Possessiveness. To keep her mate from taking a mistress.
(c)
The main point in Chapter 8
is that females will often take preventative measures in order to keep her mate
with her to get the most investment out of him that she can. For example, she
may fight off other females to keep the females away from her mate, or she may
prevent him from flirting with other females. An interesting point is that at
times, instead of being angry with her mate for courting other females, she
will take the opportunity to copulate with him again.
(d) One weakness of this chapter
was the organization of it. It did not seem to be organized at all. Instead t
jumped from topic to topic and mixed topics together.
Females of various species have evolved to fight
each other. However, unlike males, they rarely fight, and when they do, they do
not fight to kill each other. More often, these fights are more verbal than
physical. Females also usually do not fight over males, but over more
significant matters. For example, birds will fight over nests. These fights are
to assure their genes get passed onto the next generation and are more over
resources for their offspring, rather than over males to copulate with.
Females have evolved to resort to various
manipulative strategies. One way females do this is by manipulating other
females. For example, in some species of newts, the females will steal male
sperm packets left for another female. Female African butterflies will often
chase away any other females they see near their mate. Another way females are
manipulative is that they will intervene during another couple while they are
copulating or courting. For example, some toads need males to watch their eggs
for them, so in order to steal another female’s mate,
she will intervene in the mating process. An additional method females will use
is to manipulate males to make him invest more in her and her offspring. One
example of this is some male frogs must hold the eggs in his vocal sacs for a
period of about 52 days. He must do this in order for his offspring to survive.
But during this period, he is unable to sing to attract more females.
Females may also use preventative strategies to keep
her mate with her and her offspring. She wants to get as much of an investment
from him as possible. If her mate copulates with another female, he may leave
her offspring to help raise the offspring of the second female. One way she
tries to prevent her mate from courting another female is to intervene. For
example, male burying beetles will stand on their heads to attract other
females with a scent that comes from their abdomens. If he already has a mate,
and she sees him doing this, she will knock him over so he cannot attract other
females. Another example is female pied flycatchers who
will interrupt her male if she sees him singing to another female. Another method females may use to prevent her mate from
investing time in another female and her offspring is infanticide. If more than
one female mates with the same male, they will often try to kill each others’
offspring. One species that is an example of this are house sparrows. If a male
has more than one mate, he will only help the female whose eggs hatch first. So
the second female will try to kill the first female’s eggs.
Females may also use a more passive strategy to keep
her mate. A passive strategy some females use is when her mate is trying to
court another female, instead of getting angry, she
may instead use the opportunity to copulate with him again. She will actually
become aroused by his courting and act as if it is meant for her, instead of
trying to stop him. One species that does this are starlings. However, if this
doesn’t work, and she sees that another female is attracted to her mate, she
will use more aggressive actions. For example, northern harriers will
intimidate and possibly attack a rival female. Blue tits will knock their
rivals out of the air. Starlings will sing at another female to scare her off
or if she sees her mate looking at another nest hole,
she will fill it up to make it look occupied.
Females will at times fight with other females over
males. They have evolved to fight for three reasons. First, they will fight out
of desperation if there is a lack of males. Second, they will fight out of
aspiration. This is when females are choosy with who they mate with and they
strive to mate with the superior males. Third, they will fight out of
possessiveness. This is to keep her mate from taking a mistress, and to keep
him from investing in another female’s offspring.