Love as defined by genetic script

Love as defined by genetic script

Photo by Marisa Barrett on Unsplash

Originally published 13 February 2001

This week, Sci­ence Mus­ings offers Valen­tine’s Day advice to the lovelorn:

Dear Dr. Chet,

I’ve been mar­ried to Jack for sev­en years and, all things con­sid­ered, he is a good hus­band. But it seems we are con­stant­ly squab­bling — about mon­ey, house­hold chores, and whom we social­ize with. I think it all comes down to sex. Why can’t we get along?

FED-UP

Dear Fed-Up,

As behav­ioral biol­o­gist, Tim Birk­head points out in his book, Promis­cu­ity: An Evo­lu­tion­ary His­to­ry of Sperm Com­pe­ti­tion, a dis­par­i­ty of inter­ests between male and female is built into the struc­ture of life. Males are dri­ven to insem­i­nate as many females as they can, and to ensure that oth­er males don’t undo their work. Females have evolved an amaz­ing vari­ety of ways to exer­cise choice over whose sperm fer­til­izes their eggs. “Sex­u­al repro­duc­tion,” Birk­head said, “is any­thing but coop­er­a­tive.” Humans, of course, are not slaves to our genes. Treat him to a roman­tic can­dlelit din­ner on Valen­tine’s Day. Maybe he’ll bring flow­ers and chocolates.


Dear Dr. Chet,

I’m a good-look­ing 29-year-old gal with a string of boyfriends as long as your arm. Each of them wants to be my one-and-only, but I just can’t make up my mind. What’s wrong with me? Why can’t I decide?

MUDDLED

Dear Mud­dled,

Charles Dar­win, the father of evo­lu­tion, was stunned to dis­cov­er female bar­na­cles who kept a tiny male part­ner in each of two lit­tle pock­ets inside their shells. The females of cer­tain oth­er species of bar­na­cles car­ry a dozen or more “lit­tle hus­bands” inside her body, Dar­win observed, each one of which is not much more than a tiny pack­et of sperm. All of which turned the Vic­to­ri­an notion of nat­u­ral­ly monog­a­mous females on its ear. Your boyfriends may pine for exclu­siv­i­ty, but humans are not the only species in which females can pre­fer a bevy of suitors.


Dear Dr. Chet,

I am a 50-year-old man in love with a woman half my age. Am I rob­bing the cra­dle? Can it pos­si­bly work?

TROUBLED

Dear Trou­bled,

Only time will tell if it works, but a han­ker­ing for a youth­ful part­ner may be in your genes. The urge to “be first” is appar­ent­ly wide­spread in nature, anoth­er aspect of sperm com­pe­ti­tion. Some male but­ter­flies insem­i­nate females while they are still wrapped in their hard pupal cas­ing. Male thrips (a tiny prim­i­tive insect) look for females even before they have start­ed to pupate; the females then car­ry the sperm through lat­er stages of devel­op­ment, ready to lay fer­tile eggs as soon as they reach adult­hood. As species go, you’re a long way from “rob­bing the cradle.”


Dear Dr. Chet,

My hus­band and I just can’t seem to agree on the fre­quen­cy of love­mak­ing. He seems to always have sex on the mind. Most times, I’d just pre­fer a snug­gle. What’s nor­mal? Am I out of line?

HESITANT

Dear Hes­i­tant,

Your sit­u­a­tion is not all that unusu­al, but it’s hard to say how much is genes and how much is cul­ture. Con­sid­er­ing the sex lives of oth­er species does­n’t help much to answer the ques­tion. A female screw­worm fly mates only once in her life. On the oth­er hand, the giant water bug of the South­ern Unit­ed States might cop­u­late more than 100 times in a 36-hour peri­od. Males and females of some worm species lit­er­al­ly fuse their gen­i­talia togeth­er before sex­u­al matu­ri­ty and remain bond­ed for life. If you fall some­where between the screw­worm fly and the giant water bug, you are prob­a­bly normal.


Dear Dr. Chet,

My boyfriend is exceed­ing­ly gen­er­ous with gifts, espe­cial­ly on Valen­tine’s Day. The prob­lem is, he expects “some­thing in return,” and I am deter­mined to wait for a ring. How can I put him off with­out seem­ing ungrateful?

WAITING

Dear Wait­ing,

As Tim Birk­head makes clear, offer­ing gifts for sex is com­mon­place in nature. Usu­al­ly, it is food the male offers. For many grasshop­pers and crick­ets, the male pack­ages his sperm in a nutri­tious wrap­per that he attach­es to the female’s body; as she eats his Valen­tine offer­ing, his sperm leaks into her body. Although your boyfriend may be act­ing on a genet­ic script, you have no oblig­a­tion to oblige him. Take the choco­lates, but insist on the ring. That’s what being human is all about.

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