reproduction is clearly evident in certain biological traits.  As mentioned, 
human females do not have any outward displays of estrus, nor are they 
aware (in most cases) of their ovulation, so they are required, in their 
natural state, to be receptive to sex at any time.  Humans also have a very 
low fertility compared to other primates.  The sperm of human males are 
low in quantity per ejaculate, compared to non-human mammals, and are 
also about forty percent defective, much higher than any other primate. 
Human males must deposit this low quantity of defective sperm in the 
female's vagina, rather than direct into the uterus, which is behind a wall 
that is only receptive to sperm during ovulation.  These factors combine to 
make fertility in humans very low, as compared to that of other mammals 
and primates in particular.
	The low fertility found in humans is also found in both 
monogamous and polygynous primates, since the sperm need not compete 
with that of other males.  This would indicate that humans are an 
evolutionary product of either monogamy or polygyny.  Humans display 
marked sexual dimorphism, with females being approximately 80 percent 
of the size of males, although this polymorphism seems to have been 
steadily decreasing over the ages.  This sexual dimorphism is similar to 
that observed in non-human primate species that live in a mildly 
polygynous society.  Male and female members of one early human 
ancestor, Australopithecus afarensis, were once thought to be different 
species, because of their dramatic sexual dimorphism - females were a 
mere 64 percent of the size of males. Another difference found between 
the sexes in humans is the rate of maturation and the life cycle.  Males 
tend to mature later than females, die at a younger age, and be more likely 
to die, both before and after maturation, than females.  All of this evidence 
suggests the natural state of humans as a "mildly polygynous species that 
has evolved from a highly polygynous species."
	There is, however, evidence that human nature tends towards 
monogamy, although monogamy in a different sense than that which 
society tends to apply.  There are several reasons why humans might 
tend to be monogamous.  The first and most overriding reason why humans 
might tend to be monogamous involves the rearing of highly dependent 

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