Hi Barry
Thank you for your question. I have not faced this question before but felt like it deserved an answer for sure. There is no particular scripture i can find that makes it clear to me why God designed us this way. I did a little digging on the internet and found an article that addressed your question. I want to clarify that i am not sure why you asked the question but the article addresses the question to refute the evolutionists stand point of God being creator God. I do not know where you stand and do not wish to offend but thought he did a good job explaining from a scientific and creation stand point the answer to your question.
I am pasting the article into this email to share it with you.
I found it on a website called answer in Genesis, hope it helps.
If there were an all-knowing Creator, why would He design men with a structure for which they have no use? Dr. Tommy Mitchell, AiG-U.S., explains why males have nipples.
My son asked me, “Why do men have nipples?” I did not have a good answer, other than they were made in the image of God. I've searched your website because I thought I had read about it before, but cannot find the article. Can you please help me answer this question for my son, who is struggling with the “fiery darts” thrown at him in public school?
Thank you,
Amanda Clark
Dear Amanda,
Evolutionists often raise this issue as an objection to the concept of a creator God. After all, if there were an all-knowing Creator, why would He design men with a structure for which they have no use? In females, the nipple has an obvious function, that is, to breastfeed a baby. So what’s the purpose for nipples on males?
A frequently promoted evolutionary view of male nipples is that they are leftovers from our evolutionary past. They are often considered to be vestigial organs. The vestigial idea suggests they were functional in the past, but as the evolution of man progressed, their function was lost. Upon close examination, this view does not make sense. In fact, this is a very poor evidence for evolution.
If male nipples are, in fact, vestigial, they must have had a more robust function in the past. Does the evolutionist actually suggest that our male evolutionary ancestors breast-fed newborns, and that somehow as evolution progressed, this ability was lost? Alternatively, would the evolutionist argue that our ancestors were all females, that modern males diverged from this all female population, and that in this process they lost the ability to lactate?
Actually, evolution posits that mammals evolved from reptiles and that the divergence of male and female took place first in reptiles. Why then would another divergence occur as humans began to evolve? In reality, if evolution were true, then it could be argued that male nipples are still developing and that men should be able to breast-feed in the future!
The creation model provides a much better explanation for the presence of nipples in males. Male nipples are not a vestige of evolution but are instead a vestige of embryology. They in no way diminish the abilities of the creator God, but are actually another example of His wisdom. Nipples in males are actually an evidence of “design economy.”
Very early in their maturation, male and female human embryos are essentially the same. All these embryos have structures that will ultimately form the defining physical characteristics of male and female. In the early stages of development, all embryos have both the Wolffian duct and the Mullerian ducts, for instance. Under the influence of a Y chromosome, the Wolffian system develops into the internal and external structures of male anatomy, and the Mullerian ducts regress. Conversely, in the absence of a Y chromosome, the Wolffian system regresses considerably, and the Mullerian system develops to its full potentials, forming many of the female anatomical structures.
It should be clarified, however, that embryos do not all “start out female.” The genetic makeup of each individual is in place from the time of fertilization. Thus the “programming” for “male” and “female” is determined from the outset, and the anatomical gender is simply a result of the expression of those genes.
The mammary duct system and the associated nipple is likewise the same in both genders, developing during the sixth week. The rudimentary mammary duct system remains indistinguishable at birth. This tissue is hormonally sensitive, and it can, in either gender, respond to maternal estrogen transferred across the placenta by producing a secretion known as “witch’s milk.” Male and female breast tissue remains poorly developed until influenced by estrogen in the early stages of puberty in the female. If nipples and breasts are “useless” to males, they are equally useless to prepubescent girls, and for that matter are “useless” to any woman who is not breastfeeding a child.
It should be noted that male nipples are not useless, as has been suggested. They are very sensitive and are a source of sexual stimulation. Further, to characterize them as vestigial is problematic, as they are fully vascularized and have more than adequate nerve supply. Why would this be so if they were, in fact, a worthless by-product of our evolutionary ancestry?
Far from being a problem for creationists, the presence of nipples in males is actually another example of the wisdom and creativity of the God we serve. It is, in fact, the evolutionists who have a problem with this issue, as they can provide no reason for the existence and persistence of male nipples in an evolutionary scenario.
Sincerely,
Dr. Tommy Mitchell's
Pastor David Bueckert
God created man in his own image, in the image of God created he him; male and female created he them. And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. And God said, Behold, I have given you every herb bearing seed, which is upon the face of all the earth, and every tree, in the which is the fruit of a tree yielding seed; to you it shall be for meat. And to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is life, I have given every green herb for meat: and it was so. And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day." 
Despite his intelligence, man used a logical fallacy now called God of the gaps to create God. It goes like this. If I can’t think of any other reason for thunder and lightning, a God must be the cause. If I can't think of any other reason for the rain to come after three months of drought, a God must be the cause. Interestingly enough, man created God in his own image. I wonder why that sounds familiar.