What does the slang term "Joe Gland" mean?

In the 1985 novel Footfall by Larry Niven and Jerry Pournelle I came across the following paragraph:

They took out identification cards. Clybourne glanced at them, but Jenny thought he looked at them superficially. He was much more interested in the visitors than in their papers. Doesn’t miss a detail. Joe Gland, thinks he’s irresistible.

Then a bit later:

They both act that way. Of course. Not Joe Gland, just a Secret Service agent doing his job.

From the context I understood this "Joe Gland" to mean something of a self-important, maybe vain man attempting to look good in front of a woman, but I wasn't entirely sure (it doesn't really make sense), so I checked in Google, and found very little: facebook profiles, the book itself, a tweet and a forum post; so I thought I'd ask it here.

What's a Joe Gland? I suppose it's US slang, popular primarily in the 80s or earlier, or maybe never really widespread. What does it mean, when it was first used, what's its etymology?

Reader's digest did an article series back in 1970 called "I am Joe's Body" One of the installments in the series was titled "I am Joe's Man Gland" Only version I can find on line drops the subsection titles, and merely lists Joe's testis:

I am Joe's left testis. Compared to other glands, I am not bad- looking at all: a glistening, pink-white oval. I weigh four grams and am four centimeters long, two centimeters at my greatest diameter. My function is dual: to manufacture those creators of life, the sperm cells; and to produce the hormone of maleness, testosterone. This chemical assists in construction of muscle, bone and other tissues. It helps shape Joe's mental attitudes as well as his body. But for it, Joe would be soft, flabby, beardless, apathetic.

The title, its derivatives, and the attitudes expressed in the piece became a bit of a pre-internet meme.

Though I've never heard this phrase before, I'd interpret it as being a reference to a testosterone-pumped guy, as hormones are produced by glands [an organ that synthesizes hormones for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).]

Joe Gland would be implying he was one giant gland, secreting testosterone; that he had little more going for him except his bulk or drive or success or looks or whatever it is men think testosterone gives them (it certainly doesn't imply intelligence, sensitivity or humility!)

The tweet seems to confirm this.

Sitting in a coffee shop watching Joe Gland try to pick up two girls by lecturing them on Maslow's Hierarchy of Needs.

I've never heard that phrase but "Joe Cool" was a trendy phrase at that time from a Snoopy cartoon on television. Changing it to Joe Gland as a more scornful and less comic reference seems a small step.

And as medica says, a guy who is driven by glands is the meaning.