Why are males of the species always more sexually aggressive than the female?

Not true. In most insect and arachnids, it's the female who is the aggressor. And in birds and other animals, the male has to primp and preen and show off to attract a female, he can't just go after her. In mammals, the female has to cooperate with the male for sex. I don't think there's any generality that applies when it come to sexual reproduction in nature. In humans, men are more aggressive overall, not just in sex, they act more, communicate less. Women are the opposite. And humans are far too new a species on the planet to say whether this arrangement is the best for continuing the line.

Sexual aggression is simply the old way to make sure that the species survives. When men are more aggressive, the females are not as interested. However, as the male slows down the female becomes the aggressor. Males peak at 15, females at 40. Just wait. Ha Ha the joke will be on you. . .

The survival advantage is pretty clear: males can have more than one child at a time whereas women cannot. If females were more aggressive, they'd force coitus and then have to wait however long. Males don't have to wait for the other set of offspring.

In the human species I think that it guarantees that a man can impregnate as many females as possible...the stronger he is the more he can impregnate..it leads to a stronger next generation...the female however saves her energy to protect the fertilized egg...the more she protects it --the stronger she is--the more likely the egg is too survive...SO i guess because the female is busy nurturing and raising the egg to baby..it is an evolutionary advantage to have her not be so aggressive sexually and let the males do it.

The survival of the strongest, but not always is the male, among some kind of insects the aggressive one is the female, for example the tarantula kills the male after the relation and the mantis may eat the male during the copula.

Men are natural projectors and women are natural receivers. Of course this won't apply to EVERY SINGLE man or woman out there, but it's the general idea. The earth is female, and the sun and rain and air are male. When the sun, rain and air project into the female earth, things are born and the earth gives birth to them.

testosterone is the key to aggression. Males have to be able to protect the family when crap happens. If you watch lions and hyenas fighting, females will spur with hyenas -- but when the male shows up, the hyena - which sucks at sprinting - gets Saddam Husseined.

It is to the advantage of males to be relatively indiscriminate when it comes to mating. The minimum a male has to do to procreate is to have sexual intercourse. The minimum for a female is to have sexual intercourse, and carry the offspring in her womb for a significant length of time. The female spends more time and physical resources on any one pregnancy. Thus females must be more discriminating when it comes to who they have sex with.

the only thing I can think of is the women have the babies - so they make the males more aggressive to make sure the species populates.

Because males need to have a drive to spread their seed in as many females as possible to ensure that they will have a large offspring.