The Trenton Line into Center City: A couple of guys tap at their iPads, cruising e-mail, scores, stocks, games. A few women are immersed in their Nooks or Kindles.

If you've ever seen this picture, you've seen support for studies of how we use new media such as tablet computers (iPad, HP Slate, Motorola Xoom) and e-readers (Nook, Kindle, Sony Reader).

In a study released in August, Forrester Research found that 56 percent of computer tablet owners are male, while 55 percent of e-reader owners are female.

That jibes with long-remarked trends. Women buy more books than men do. A Bowker survey published in 2010 had them buying 64 percent of all books. Women read an average of nine books a year, men five. It makes sense women would buy more e-readers. It also makes sense they'd be reading Pride and Prejudice or Water for Elephants: In the United States and Canada, women buy about 80 percent of all fiction sold.

Human beings are not born hooked up to an iPad. What if we are applying the really old ways - evolutionarily developed characteristics and skills - to new media?

What if men are using their tablets as rocks and spears to pry loose the goods, kill the mastodon, and get back in the cave? What if women are e-reading to learn the signals, track the emotional, sexual, and social resources to build community, connection, family?

"My wife wanted a simple, essentially single-purpose reader device," says iPad user John Michael McGinty of Aldan. "Me, I wanted options, settings, and multifunctioning."

Maria Hutchinson of Haddonfield says husband Bobby "loves his iPad, and I am hooked on my Nook Color." (Barnes & Noble's Nook Color is a dark-horse hit with women, who are subscribing in large numbers to full-color magazines and best-sellers, often outselling iPad subscriptions.) "I don't really care about all the applications, music, or games. I just wanted to be able to read. My husband has an app for everything."

And Wayne Leibel of Easton, Pa., shamefacedly admits: "I have an iPad and use it, but never to read books."

"These technologies very much play to our biology and neurology," says Matt Richtel, the Pulitzer Prize-winning New York Times technology reporter. "There's a reason this stuff has been adopted so quickly: It's playing to very essential human needs that go back millennia, eons."

Imagine us back on the primeval veldt, scrambling to survive. We are, biologically, nearly identical to that human being. What has changed, with increasing speed each year, is human culture.

So when we need behaviors, as in What do I use this thing for?, we reach back into a bag of tricks we've had on our hip for 200,000 years.

Clinical psychologist Simon Baron-Cohen of Cambridge University, author of The Essential Difference, says that "males on average have a stronger drive to systemize," consistent with the idea that they may be more technology-focused. In an e-mail, he writes that "females on average have a stronger interest in empathy," compatible with the notion that they are more interested in novels, "especially narratives describing characters' emotional and mental states." Like a good researcher, he wants to see more science on the matter.

Louann Brizendine, neuropsychiatrist at the University of California, San Francisco, and author of The Female Brain and The Male Brain, says studies showing "women use e-readers more and men use iPads more may be related to the brain-scan findings showing the male brain gravitates to the visual circuits for pleasure and excitement more. The female brain, of course, activates the visual circuits, too, but not as exclusively."

Like a rock, a spear, or an agarose monosuspension for single-cell gel electrophoresis, an iPad is a tool. It can be used as an e-reader, but, like Leibel, men tend to use tools for systematic, instrumental purposes. And their brains like it. Most people who play video games - in which you capture territory and kill aliens and gain rewards - are males 18 to 34 years old. And a 2008 Stanford University brain study showed that, while both men's and women's addiction centers light up during play, male brains light up more, especially when they win territory.

Men can be empathetic - but maybe empathy didn't work for hunters on the veldt. If you feel for the rhebok or person you must kill, the less of a hunter you'll be.

Women can be systematic. The right and left hemispheres of the "average" female brain, however, seem more nearly balanced than in the average male brain, with its beetlingly dominant left half. Studies (still controversial) by neurologist Ya-Wei Cheng suggest that the female brain may respond more strongly to the actions of mirror neurons, cells that register the expressions and reactions of other people and prompt efforts to complement them. Reading, and fiction specifically, may engage and reward that aspect of the female mind.

We are fabulous beings, fashioners of modern tools that serve our ancient needs. Richtel quotes a high school principal who once spoke a line of unwitting poetry: "He said something like, 'These tools just let us be extreme versions of ourselves.' "

Contact staff writer John Timpane at 215-854-4406, jt@phillynews.com, or @jtimpane on Twitter.