More about penis spines

I kept trying to find something acceptable to show regarding the spines found on some other mammals, following the previous post’s topic. Here is a nice drawing that demonstrates the differences:

You can see the raised bumps on the mouse penis.  Think of them as whiskers for the penis. This figure is from a paper entitled A histological study of the development of the penis of wild-type and androgen-insensitive mice. What they did was look at mice that had lost the ability to respond to androgens, the hormones responsible for most male development.

As seen in the paper, the spines on the outside of the penis disappear when androgens don’t work properly, along with lots of other things. The Nature paper describes a small deletion in non-coding DNA, so it does not effect whether a protein is made or not. What the region, called an enhancer, does is affect the expression of the gene.

In this case, it is the androgen receptor, the same sort of gene affected in the mouse figure above. As the authors of the current Nature paper say:

Profound changes have also evolved in the genitalia of humans compared to other animals. Many mammals have keratinized epidermal spines overlying tactile receptors in the glans dermis. Penile spine growth is androgen-dependent, as primates lose spines upon castration, and treatment with exogenous testosterone restores spine formation (Fig. 2k). Mice with AR protein-coding mutations fail to form penile spines, confirming an essential role for AR in penile spine development. Our results show that humans have lost an ancestral penile spine enhancer from the AR locus. Humans also fail to form the penile spines commonly found in other animals, including chimpanzees, macaques and mice (Fig. 2l). Simplified penile morphology tends to be associated with monogamous reproductive strategies in primates. Ablation of spines decreases tactile sensitivity and increases the duration of intromission, indicating their loss in the human lineage may be associated with the longer duration of copulation in our species relative to chimpanzees. This fits with an adaptive suite, including feminization of the male canine dentition, moderate-sized testes with low sperm motility, and concealed ovulation with permanently enlarged mammary glands, that suggests our ancestors evolved numerous morphological characteristics associated with pair-bonding and increased paternal care.

So, we lost our penis spines and whiskers as well as having decreased tactile sensitivity, smaller balls, feminine teeth and slower sperm but gained endurance, larger penises and breasts. I think most men will go along with the consequences.

Interestingly, the paper mentions that all the internal apparatus for producing penis spines might still be present. When they put the enhancer region from chips into human skin cells, they see a large increase in specific gene expression. So all the rest of the genetic apparatus may still be there. I wonder if men with Hirsuties coronae glandis express some barely function form of the enhancer. Maybe they have different facial hair also – perhaps real whiskers.

This suggests that perhaps we could add back the receptor and get penis spines back. Maybe put the genetic sequence in a hand cream that could be used. The skin cells take up the DNA and away we go. Of course, one would want to use gloves when doing this since we would not want to see hairy spines growing on our palms.