NETTIE STEVENS: BIOGRAPHY AND CONTRIBUTIONS - CULTURE VOCABULARY - 2025

Nettie Stevens (1861-1912) was a leading scientist and geneticist of the early 20th century, best known for being one of the first scholars to describe and specify the chromosomal bases that determine sex in species.

Stevens, a native of Vermont (United States), also made numerous contributions in the field of embryology, a discipline that studies embryonic development from conception to birth; and in the field of cytogenetics, a discipline that encompasses the function and behavior of chromosomes.

The work that immortalized Nettie Stevens in the history of science was published in 1905 under the title Studies in spermatogenesis with special reference to the "accessory chromosome."

In this work a deep cellular and chromosomal investigation is carried out taking into account a species of beetle named as Tenebrio molitor or mealworm, as it is commonly known.

Biography

Nettie Stevens was born on July 7, 1861 in Cavendish, a small town located in Windsor County, Vermont.

His parents were Ephraim Stevens and Julia Adams, who had four children counting Nattie; however, both boys died at an early age, so only Nattie and her sister Emma survived.

Tragedy seemed to haunt the Stevens family, as Nettie's mother also passed away in 1865. Shortly after her father remarried, so the family had to move to Westford, another town in Vermont located in Chittenden County.

First studies

In the town of Westford, Nettie studied at a school in the public education system, where the young woman soon discovered her academic inclinations and scientific abilities. In fact, both Nettie and her sister Emma stood out for their excellent grades and school skills.

Even at the school, called Westfield Normal School Nettie Stevens, she managed to complete a course in two years, when it usually took four years.

After finishing her school studies, Nettie was the first in her class; Along with her sister, she was one of the first women to complete school in an 11-year period in 1880.

University education

Her economic situation forced her to work at an early age as a school teacher: she taught Latin, English, mathematics, physiology and zoology; in addition, she was a librarian. Thanks to these jobs she managed to save a certain amount of money, which was destined from the beginning to finance her university studies.

At the age of 35, he managed to go back to study after having done hard work. In 1896 he entered Stanford University, currently located in California, near San Francisco. She then completed her master's degree in 1900, whose doctoral thesis was titled Studies on Ciliate Infusoria and was her first published work.

Chromosomes and sex determination

Nettie Stevens had developed since 1903 a notorious interest in knowing the relationship between chromosomes and determining sex; therefore, she decided to apply for a grant in order to carry out her research.

Thanks to his excellent academic record, he was awarded the financial subsidy; This allowed Nettie to publish in 1905 his important work entitled Studies in spermatogenesis with special reference to the accessory chromosome, in which he was able to verify that chromosomes exist as even structures within our cells.

Death

Nettie Stevens passed away on May 4, 1912 at age 51 at Johns Hopkins Hospital, located in Baltimore, from terrible breast cancer.

She was buried along with her father Ephraim and her sister Emma in the Westford, Massachusetts cemetery. Her scientific career only spanned nine years of her life.

Contributions

Investigation method

Stevens's discoveries are admirable for many reasons; One of these is that the researcher carried out a clear and concise methodological study, the observations of which had a detailed and rigorous description.

In addition, connoisseurs say that their interpretations had a remarkable lucidity, at a time when Mendelism was not yet fully handled, a genetic theory based on Mendel's laws corresponding to hereditary transmission in living beings.

Stevens' research allowed a step forward in the development of biological knowledge, since the author managed to attack a key area of ​​what was unknown about chromosomes and how sex was determined.

Approaches prior to Stevens's work

In the 19th century, different theoretical approaches were presented on how sex is determined in living beings. Some of these were as follows:

Externalist approach

This theory explained that the sex of individuals was determined by environmental conditions, which influenced the development of the embryo or the egg, depending on the species.

Internalist approach

In this case, it was argued that sex was determined by factors that occurred within the same egg or embryo.

Hereditary or Mendelian approach

Sex is determined at fertilization and by fertilization; however, its emergence is hereditary in nature.

X and Y chromosomes

Stevens was able to corroborate that there are twenty large chromosomes within the somatic cells of the female; that is, ten older couples. It is important to clarify that somatic cells are those that are responsible for the growth of tissue and organs existing in any living being.

On the other hand, within the somatic cells of the male, there are nineteen large chromosomes and one small, which means that in total it stores nine pairs of large chromosomes, and one formed by a small and a large chromosome.

Man as a determinant of sex

In other words, the scientist Stevens realized that sperm are what determine the gender of the species, since they can store one smaller chromosome or ten pairs of chromosomes of the same size.

Therefore, the author was able to establish that if a sperm cell contains the ten pairs of chromosomes of equal size, the embryo will be female; but if the sperm contains 9 pairs of equal chromosomes and a smaller pair, the embryo will be male.

To differentiate some chromosomes from the others, it was decided to classify sperm into two parts: it can then be said that there are sperm that have the X chromosome (that is, those that will provide a female) and those sperm that have the Y chromosome (that is, that is, those that will fertilize a male).

Today this information can be accessed from any biology book or through the internet; however, at the end of the 19th century this classification was ignored. For this reason, Stevens's discovery made a remarkable difference in the development of science.

Recognition

Notwithstanding the significance of Nettie's discovery, it was not acclaimed as it was at the time of publication. In fact, Stevens' findings did not receive the necessary attention until 1933, when genetic knowledge had advanced a little further.

It is believed that this lack of recognition was due to the fact that the biological significance of the sex chromosomes could not be properly appreciated until many years after their death. In addition, due to the historical context, being a woman placed her below her male colleagues.

Although Stevens had received support from various scientific institutions during her research, the author did not receive any material recognition or reward for the results of her work. In fact, Nettie's work was initially shelved by Bryn Mawr College.

It was only in 1912 when this institute decided to create a research professor position especially for her; however, Nettie did not hold this position as she passed away shortly thereafter that same year.

Controversies

When reading or researching the way in which sex is determined, in most biology manuals or encyclopedias this discovery of the "accessory chromosome" is attributed to important people like McClung.

Similarly, Wilson is also credited with interpreting the sex chromosomes, leaving aside the name Stevens.

In the best of cases, it is often said that this discovery was made by Wilson and Stevens, which makes readers think that both scientists worked together, with Nettie being only an assistant to the other scientist. Sometimes the finding is even attributed to another renowned researcher, such as Morgan.

However, although Wilson did research on sex chromosomes in insects like Steven, publishing both on the same date (1905), Wilson's work deviates from Mendelian theory, while Stevens's work was influenced by this theory..

In other words, the Stevens name was dropped as, at that time, Wilson had a well-deserved reputation as a researcher and a remarkable scientific career.

Despite this, at present attempts are made to vindicate the work and findings of Nettie Stevens, being one of the most acclaimed women in the world of science.

References

1. Echeverría, I. (2000) Nettie Maria Stevens and the function of sex chromosomes. Retrieved on September 15, 2018 from DigitalCSIC: digital.csic.es
2. Santesmases, M. (2008) Women, biology, feminisms: a bibliographic essay. Retrieved on September 15, 2018 from DogtalCSIS: digital.csic.es
3. Bailey, M. (1981) Nettie Maria Stevens (1861-1912): Her Life and Contributions to Cytogenetics. Retrieved on September 15, 2018 from Jstor: jstor.org
4. G, Brush (1977). Nettie M. Stevens and the Discovery of Sex Determination by Chromosomes. Retrieved on September 15, 2018 from The University of Chicago Press: journals.uchicago.edu
5. H. Morgan (1904) Experiments on polarity in Tubularia. Retrieved on September 15, 2018 from Wiley Online Library: onlinelibrary.wiley.com