July 7 - Happy Birthday, Nettie Stevens

  Posted on July 7, 2022     

This is an update of my post published on July 7, 2011:

Most famous for her discovery of the chromosomal difference that (usually) determines whether an animal is male or female, Nettie Stevens is one of the first American women actually recognized for her contribution to science!

Nettie Stevens was born in Vermont on this day in 1861. She studied at Westfield Normal School in Massachusetts, graduating at the top of her class, and she earned B.A. and M.A. Degrees from Stanford University, in California. Finally, at Bryn Mawr (in Pennsylvania), Stevens studied insects and was able to identify the Y chromosome in a species of mealworms. She completed her PhD at Bryn Mawr in 1903.

This is Nettie Stevens pictured with X (above)
and Y (below) chromosomes.

 

You might know that most mammals have two sex chromosomes. Oversimplifying a bit, males have one X and one Y chromosome, and females have two X chromosomes. (That's an oversimplification because, first, there are individuals who have only one sex chromosome and others who have three; second, there are some conditions in which individuals with XY chromosomes develop female reproductive structures and individuals with XX develop male reproductive structures. Add to all of that the fact that, in humans at least, there is a wider range of gender identity than just male/female.)

Getting back to animals' sex chromosomes: although some insects such as fruit flies also have X and Y chromosomes, many animals do not have sex chromosomes. In some cases a creature's sex is determined by the environment. For example, if an egg is kept at one particular temperature, the developing creature becomes male; at another temperature, the creature develops into a female. 

Some animals (about one third of all animal species, other than insects) have both male and female gametes and are either born male, later becoming female if necessary, or vice versa. Clownfish like Nemo fall into this category. Also, most plants are hermaphrodites.

Of course, some organisms are asexual - they don't have sexes at all.

An example of asexual reproduction:
a hydra budding off a "baby" hydra.

Also on this date:

Running of the Bulls in Spain  

Figure skater Michele Kwan's birthday

Musician Ringo Starr's birthday

Independence Day for the Solomon Islands

Saba Saba Day in Tanzania

Anniversary of Olivier Levasseur giving the world a challenge

Unity Day in Yemen

Tell the Truth Day

Tanabata Matsuri (Star Festival) in Japan

Plan ahead:

Check out my Pinterest boards for:

• July holidays
• July birthdays
• Historical anniversaries in July
  
  

And here are my Pinterest boards for:

• August holidays
• August birthdays
• Historical anniversaries in August

October 26 – Intersex Awareness Day

Posted October 26, 2018

There are some people who insist that male is male and female is female - period! End of sentence.

These people often make some sort of reference to "that's just nature!" or "anything else is unnatural!"

These people don't seem to understand that "nature" is complex and varied. Here's some science that is important to understand in order to even discuss the topic:

First, loads of animals don't have "male" and "female" at all. For example, jellyfish have "babies" by asexual reproduction, in which polyps protrude and then break off to grow up to be new jellyfish.

Some animals, such as copperhead snakes, have males and females but still - sometimes - make baby snakes through asexual reproduction.

Some animals that have males and females have some interesting differences from MOST male / female roles - like seahorses, in which males are the ones that get "pregnant" and give birth.

Some animals change sex from female to male or from male to female, depending on their age or the need of their group. Some examples are  clownfish and moray eels.

A few animals are born with both male and female sex organs. One example is banana slugs.

At least one animal - whiptail lizards - has all females! No males.

In a few species, males regularly mimic being females. Examples of this include garter snakes and cuttlefish.

Okay - enough about "nature" and other animals. What about humans? Maybe, when it comes to humans, male is male and female is female?

Nope.

When it comes to male or female, we generally go by body parts, and some people are born with some body parts usual in girls, AND some body parts usual in boys. Some people are born with ambiguous body parts that include parts that are not usual in either boys or girls. All of these people are called "intersex." 

Remember, intersex has to do with bodies. It is not a term that considers what gender people identify as (whether people identify as a girl / woman or a boy / man) or what gender people are attracted to.

There is a television show with a main character who is intersex.

Another way that we can discuss male and female is to look at chromosomes: males generally have XY chromosomes, and females generally have XX chromosomes. But, again, nature is complex. Some people are born with XYY, just X, XXX, XXXX, or (maybe) other variations. 

Also, some people are born with XX chromosomes but male body parts, and some people are born with XY chromosomes but female body parts. There are a variety of reasons for this kind of mismatch between genotype (chromosomes) and phenotype (bodies). One example is androgen insensitivity syndrome - people with this syndrome have cells that do not respond to male hormones, so they develop as females although they have the XY chromosomes that normally go along with males.

Supermodel Hanne Gaby Odiele
chose to share with the world that she is intersex.

She has androgen insensitivity syndrome.

Confusing? Biology is really complicated, but living things are also amazing and fun to learn about. I hope you are more aware of intersex, now - and THAT's what this day is all about!

Also on this date:

Angam Day in Nauru  

Austria's National Day

Cereal manufacturer C. W. Post's birthday

Mule Day

Anniversary of the opening of the Erie Canal

Armed Forces Day in Benin

Frankenstein Friday

St. Demetrius's Day

Plan ahead:

Check out my Pinterest boards for:

• October holidays
• October birthdays
• Historical anniversaries in October

And here are my Pinterest boards for:

• November holidays
• November birthdays
• Historical anniversaries in November
  

July 7, 2011 - Happy Birthday, Nettie Stevens

Most famous for her discovery of the chromosomal difference that determines whether an animal is male or female, Nettie Stevens is one of the first American women actually recognized for her contribution to science!

She was born on this day in 1861. She studied at Westfield Normal School in Massachusetts, graduating at the top of her class, and she earned B.A. And M.A. Degrees from Stanford. Finally, at Bryn Mawr, Stevens studied insects and was able to identify the Y chromosome in a species of mealworms. She completed her PhD at Bryn Mawr in 1903.

You might know that most mammals have two sex chromosomes. Those individuals who are male (men and boys) have one X and one Y chromosome. Females (women and girls) have two X chromosomes. Some insects such as fruit flies also have X and Y chromosomes. Many animals do not have sex chromosomes, and in many of these creatures sex is determined by the environment. For example, if an egg is kept at one particular temperature, the developing creature becomes male; at another temperature, the creature develops into a female. Some animals have both male and female gametes and are either born male, later becoming female if necessary, or vice versa. Clownfish like Nemo fall into this category. Many animals and most plants don't have separate sexes at all.

Older students might like to read a Smithsonian article on sex determination.