July 7: Nettie Stevens discovers sex chromosomes, plus Robert Heinlein, Sir Arthur Conan Doyle, first thumb reattachment

Nettie Stevens and the discovery of sex chromosomes

Born on this day in 1861 was Nettie Maria Stevens, an American geneticist. Despite the challenges of her time – the Civil War had just started, and it wasn’t exactly an era in which educational options for women were strong – she was one of the first American women to achieve recognition for her contributions to scientific research.

Nettie stevens
Credit: The Incubator (courtesy of Carnegie Institution of Washington)


Her most significant contribution was as one of the first scientists to find that sex is determined by the presence or absence of an X chromosome. This came about when she was studying the mealworm and found that the males made reproductive cells with both X and Y chromosomes whereas the females made only those with X. She deduced that sex is inherited as a chromosomal factor and that males determine the sex of the offspring.


First successful thumb replantation

In 1965, Shigeo Komatsu and Susumi Tamai performed the first successful surgery to reattach a completely amputated thumb.

By 1992 they had reattached 331 digits at the Orthopaedic Clinic of Nara Medical University Hospital, Kashihara, Japan.


Robert Heinlein born; Sir Arthur Conan Doyle dies

On this day we remember two authors who made significant contributions to the public perception of science and reason.

Robert Anson Heinlein was born on this day in 1907. Heinlein is a seminal figure in “hard” science fiction due to his extensive knowledge of engineering and the careful scientific research demonstrated in his stories. His works emphasise the importance of critical thinking, and he is widely regarded as the first author to depict what we would now call a mobile phone, in his 1948 novel Space Cadet – which also gave us the term “space cadet”. Heinlein co-narrated the live CBS coverage of the Apollo 11 moon landing with Walter Cronkite, and the Heinlein crater in Promethei Terra, in the southeast end of the Hellas quadrangle of Mars, is named after him.

Sir Arthur Conan Doyle died on this day in 1930, aged 71. His character Sherlock Holmes showed the power of the scientific mind, searching through data to come up with a hypothesis.

Doyle studied medicine at the University of Edinburgh and served as the doctor on a whaling ship in the Arctic. He struggled to make a living as a physician on his return to dry land, so turned to writing.

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