Pretending to have a baby to score? Fish do it

For our species and many others, fatherhood is sexy. According to one recent study, women are so attuned to fatherhood potential that they can tell whether a man likes kids by just looking at him. In other species, females won't give you a second glance if you're not already a devoted and prolific father.

For many fish, "being fatherly seems to be a strong signal to the female to mate," says Mark Sabaj, an ichthyologist at the Academy of Natural Sciences.

It poses a big catch-22 if you have to be a father to become a father. How can a guy break in?

In some species, such as sticklebacks, males will steal eggs from other males. In one type of minnow, says Sabaj, a male will oust a rival from his nest, treating most of the other guy's eggs as caviar but leaving behind just enough to fool a female into thinking he's a nice single dad.

Another popular tactic is fakery. This, Sabaj suspects, might explain one weird-looking catfish he's seen in various South American waters. Called a bristlenose pleco, the female looks normal enough but the male sprouts dozens of wormlike tentacles from his head.

Could the tentacles have evolved because females started mistaking them for fish larvae? A similar tactic almost worked for Hugh Grant's character when he borrowed a friend's child to help him score in the 2002 film, "About a Boy."

Other fish display fleshy yellow knobs or spots on their fins that look like eggs. So why not larvae? And the male bristlenose catfish is under pressure to look desirable since he has to be chosen by a female. Males stake out cavities in rocks and wait like eager young girls at a middle-school dance as the females swim by and inspect them. The females look for males tending larvae, or so they think.

Once she makes her choice, a female enters his cavity, lays eggs all over the walls, and leaves. This may not sound like hot sex by our standards, but to them, apparently, this is as good as it gets.

For all his trouble, once the male fertilizes the eggs and becomes a real father, he ends up with all the parenting and housework. "He uses his fins and mouth to clean the eggs and clear the cavity of detritus ... and aerates the clutch by fanning it with his pectoral fins," Sabaj wrote in a scientific paper co-authored with Jonathan Armbruster and Lawrence Page.

While a number of fish species put the parenting burden on the fathers, others dump everything on the mothers, Sabaj says, and in still others, nobody does anything but release sperm and eggs.

The advent of larvae-imitating tentacles would seem bad for bristlenose catfish females since it foils their mating strategy. If they're going to cut-and-run, it benefits them to gauge who's a good father. But that's how evolution sometimes works, benefiting one sex at the expense of the other.

In the human world, there's no pressure on men to sprout appendages that look like adorable babies since women don't insist on previous fatherhood experience. But we do care whether men care about children, say researchers from the University of Chicago and the University of California, Santa Barbara.

They took a group of 39 male college students and tested their interest in children by showing them pairs of pictures — one of a baby or child under about 6 and one of an adult. By asking which photos the men preferred to look at, they estimated their subjects' baby interest, said Chicago biology professor Dario Maestripieri. Some chose all babies, he said; others chose all adults.

Then the scientists snapped neutral expression headshots of the men and showed them to undergraduate women, asking them to rate each man's interest in children.

"We were surprised," he said, that the men the women thought liked children were the same ones who tended to prefer the baby pictures. The study was presented at a recent meeting of the Human Behavior and Evolution Society in Philadelphia.

The scientists also measured testosterone levels and found this unrelated to how much the men liked kids. When asked whom they'd like for a short-term hook-up, said Maestripieri, the women chose the men with high testosterone, "but for the long term, they picked the guys who liked babies."

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