The explanation that the kiss is a gene didn’t match with  scientists opinions, because it is not practiced by all human societies. There are several theories that try to get closer to the memory of feeding breastfeed, or how the ancestors  feed their chickens (see how they feed the birds or mammals chickens after no longer breastfeeding). Although their  teeth are grown, mother persist in behavior just to love them. In support of the idea that the kiss is more learned than instinctive is that not all humans kiss. Some tribes do not do that. While 90% of people kissing, 10% have no idea what they lose. Others believe that the kiss is inborn and make statements in favor of this the evidence that animals practice the same motion. Today I found the motivation that the kiss is to help us out if we have chosen the right partner. When the girls are coming, the boys hormones communicate changing information about how strong  will be the children that we do with that partner. According to LiveScience, for example, women prefer the smell out of men whose genes for some specific proteins of  the immune system is different. This match could give birth to children with a stronger immune system, and with greater chances of survival. Last but not least there is the pleasure explanation. The tongues and our lips are invaded by nerve terminations  that help enhance the sensations for those that are in love and their lips touch.