That is why a man leaves his father and mother and is united to his wife, and they become one flesh.
Polygamy has been practiced and continues to do so among different religions and societies but it is my understanding that focusing on one person makes the relationship work rather than being married to multiple people and split the same amount of time between different wives and kids.
I would say that we are in fact designed to find one partner and to stay with them for as long as possible. It is something that we have been doing for centuries now, and I fail to see why all of a sudden it is a better idea to not do so.
A monogamous relationship allows for a deeper connection and offers better support and structure for any offspring. Promiscuous behavior not only spreads disease but also results in offspring that generally are not offered the support of a family structure emotionally or financially. We have survived through our social structures and communities which are large groups of long-term relationships. Short term does not allow for the development of the powerful family structure.
For males, it wouldn't make evolutionary sense for them to be designed for long-term monogamous relationships. The more women a man impregnates, the more he propagates his genes. Ergo, promiscuity is selected for. For females, they would probably be less likely to be promiscuous, since they are limited in the number of children they can have. Still, there is no reason why monogamy would be an evolutionary advantage. Also, look at the divorce rate. If we were designed for long-term monogamous relationships, it wouldn't make any sense that half of marriages would end in divorce. Monogamy is the result of cultural conditioning.
Look at all the other animals on the planet. Males seek to seed as many females to promote offspring. Women are drawn to a dominant strong male to breed with then a reliable male to remain with. Makes sense that women are prone to change who they are attracted to depending the time of their breeding cycle. Men on the other hand are just interested in breeding. Just look at the divorce rates. Surely its not a multitude of bad choices. Its just biology. And yes I'm happily married, it's just an observation.
There is an ethnic minority in China where traditionally the mother and her brothers raise the kids. The father is never known. Men and women have sex with each other with no commitment. And this has been the way they've done it for thousands of years. Science also suggests that much earlier in human history we were all polygamists.
The phrasing of this is a bit ambiguous so I'll attempt to make the distinction. I don't believe it is specifically in the DNA of human beings to be monogamous beings. I do, however, believe standards and traditions of society have conditioned us to think we are designed that way.