Google honors geneticist Nettie Stevens

I first heard of Nettie Stevens (1861-1912) when I was studying Mendelian genetics in college. She is well known to those of us who studied that branch of genetics (what I call “real” genetics!), but has been largely forgotten despite her immense contribution to the field. What was it? Nothing less than discovering that sex, at least in the species she was studying, was determined by chromosome constitution. And that turned out to be the case for many, many animal species (and even some plants!).

After years of of training, Stevens settled at Bryn Mawr College, and it was there that, while studying the mealworm Tenebrio molitor, she realized that while the cells of females had near pairs of regular-sized chromosomes, males had, among the regular pairs, one regular-sized chromosome paired with a tiny one. Those proved to be the X and Y, respectively, just as in humans. (In some species, like birds and butterflies, the females have the big and little chromosome, called Z and W respectively, and it is females that are heterogametic. In mammals and most insects, it’s the males who are heterogametic, which is what Stevens found.)

Stevens published her result in 1905, the same year that geneticist and cytologist E.B. Wilson also described the chromosomal basis of sex determination.  Today Wilson is largely given the credit for this discovery, but that’s solely because he was more famous than Stevens—and because he was a man, possessor of a Y.

It’s also typical of that era, and of the low status of women in science, that Stevens didn’t gain a regular university research position. It’s ironic that this is almost certainly because she was XX rather than XY!  Eventually she was offered such a position, but died of breast cancer before she could accept it.  She was only 50 years old.

You can read more about Stevens’s work on sex determination, detailed in a journal article, here.

Here’s today’s Doodle of Stevens, clearly based on the photo below it:

Screen Shot 2016-07-07 at 9.19.44 AM

There aren’t many pictures of her, but I like this one:



  1. ThyroidPlanet
    Posted July 7, 2016 at 11:38 am | Permalink

    I have criticized the Google Doodle here, but I must say this one is pretty good – never heard of the honoree, a bunch of interesting particulars get churned up, brain things – what would I do if I saw such chromosomes and had no idea of sex determination?

  2. merilee
    Posted July 7, 2016 at 12:09 pm | Permalink


    • jimroberts
      Posted July 7, 2016 at 2:26 pm | Permalink


  3. Willard Bolinger
    Posted July 7, 2016 at 12:53 pm | Permalink

    Jerry Coyne, thank you again for the information about Nettie Stevens. I will do a search about her and look for a book about her!

  4. µ
    Posted July 7, 2016 at 1:25 pm | Permalink

    It says on Steven’s Wikipage that “Stevens brought the fruit fly Drosophila melanogaster into Morgan’s lab as an experimental organism”.

    I try to imagine that had not happened. All those later Drosophila biologists may have worked on sea urchins and frogs (T.H. Morgan’s other research). I wonder how those later Drosophila researchers feel about their fate in that alternate universe. Research bound in shallows and in miseries; or not?

  5. Mark R.
    Posted July 7, 2016 at 3:32 pm | Permalink

    I noticed that the person who created the Google Doodle also referenced the photo you posted. Same exact pose.

  6. Bill Morrison
    Posted July 7, 2016 at 4:33 pm | Permalink

    To answer the question as to how the X chromosome got its name we have to go back to the work of Henking in 1891. He observed an “X element” in meiosis in a wasp. It was called “X” because of its mysterious nature and not because of its shape. The Y was so named by Stevens for alphabetical reasons.

  7. Iamcuriousblue
    Posted July 7, 2016 at 5:34 pm | Permalink

    Unfortunately, this recent publicity is generating gender war propaganda of its own, with the accusation that EB Wilson basically stole the discovery of allosomes from Nettie Stevens, rather than having an independent discovery in his own right:

    Anything to fit a narrative, I guess.

  8. Posted July 11, 2016 at 7:43 am | Permalink

    Reblogged this on The Logical Place.

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