The Male nipple serves no evolutionary function, yet it remains in the Genomic code. Is there only one Gene for the human nipple?

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    $\begingroup$ Perhaps the answer is that there are not two entirely different genomes, male and female, but a genome which is at least 25/26ths identical. So (simplistically!) the basic "make a breast" machinery (and pretty much everything else) exists in both males and females, but is only switched on in females, at puberty. But hormones can activate breast growth in males, either through disease or deliberately, as part of a sex change. $\endgroup$
    – jamesqf
    Oct 9, 2017 at 5:41
  • $\begingroup$ A small percentage of males today are able to lactate like the female. Maybe at some point in the past, the male species were also capable of feeding offspring in case the female perished. Also, in some males the nipple is an area of sexual stimulation. So, it does serve a purpose. $\endgroup$
    – user37021
    Oct 11, 2017 at 16:04