Except it isn't just for that, as we can infer from its "design." Consider the other possibilities:
Many other mammals have estrus; they go into heat. They're only interested in sex at times when it's likely to be procreative. Humans don't go into heat; they're still interested in sex even at times in the menstrual cycle when the female isn't fertile.
Many other mammals - including some of our closest relatives - have overt ovulation; obvious outward signs for when the female is fertile. Humans, OTOH, have covert ovulation; there's no obvious outward sign when a female human is fertile.
So... considering:
- our "design" has us interested in sex at non-fertile times, despite the fact that we could have been "designed" to only want sex when it's procreative, and
- our "design" deprives us of one of the most common tools an individual uses to only have procreative sex, if so inclined,
... tell us why on Earth you think that our designer intends for sex to be only for procreation.
Well, I'm glad you asked......
In creating humankind in his own image, he gave them qualities that animals do not need since their survival and reproductive cycles are programmed almost entirely by instinct. As a breeder of birds and dogs, and having lived in the 'ruraIs' for many years, am fully aware of how the reproductive cycle works. I am also aware that sex in the animal kingdom has nothing to do with "love"....which is one of the Creator's most dominant qualities....it has more to do with pheromones and instinct, so unless the female is ready to breed, the boys get buzzed off....sometimes violently.
The blokes are basically ready for sex any time the female is ready in nature, but in humans it is much more than an 'itch' that needs 'scratching'....or it should be. Sex produces children, sometimes as an unwanted 'side effect' of their 'scratching'......for humans this is unacceptable because we are governed by a much higher law. (whether we obey it or not) We should be respecting the transmission of life as something sacred......as God does, which is why there were so many laws governing sexual conduct in the Law of Moses. He made no such law for animals.
Since love can be expressed in many ways in the human kingdom, sexual expression is much more than a mechanical act designed to produce offspring. It is a legitimate expression of a deeper kind of love and intimacy between a committed couple. This is why humans have the institution of marriage and animals do not.
Mother animals and birds will raise their young with or without support from the fathers of their babies......some animals will mate for life...others are quite promiscuous...it all operates by programming. Since there is no morality in the animal kingdom, it makes little difference them or to God.....but humans are not like animals.....they have a moral code and the faculty of conscience. They also have a strong inbuilt sense of betrayal when a mate is "unfaithful" (married or not).
We also have a monthly cycle, rather than being fertile only once or twice a year, which means that we can have babies all year round, rather than just in one or two seasons.
We are created to reflect the kind of love that the Creator displays....deep and devotional......not the kind that animals usually display.
How does evolution explain this difference....don't tell me, let me guess....."natural selection"