Monday, June 18, 2012

Gender: Part One

Note: this program first aired on June 16, 2012.

We humans tend to think of gender as a fixed and clear cut matter. Males are males, females are females, and they each have a fixed and distinct biological role in sexual reproduction. Unfortunately, many of our human cultures have not displayed much tolerance for individuals who have blurred the lines of our clear cut ideas about gender.
What I would like you to know today is that in nature, gender is not as fixed or defined as we humans would like to think. Initially gender in the form of separate sexes arose as a result of sexual reproduction, which is simply the recombination of genetic information. In its simplest form, an individual is “encoded” by two sets of genetic information, one from one parent and one from the other. Without going into detail about the steps of meiosis (the process of making sperm and eggs) understand there is nearly infinite variation on the sets of genes that each parent can give, which is why each individual that results from sexual reproduction is completely and utterly unique.
When put this way, the obvious question is: Why do parents have to be two separate genders? Why couldn’t two individuals simply exchange gametes? Why is there gender at all? It turns out, initially, there wasn’t gender. This makes sense, the earliest organisms on earth were bacteria, and bacteria don’t have gender (nor do they generally reproduce sexually, but that is a different matter). Sexual reproduction in higher multicellular organisms was achieved through isogamy (a genderless exchange of gametes—many fungus and algae still reproduce this way).  Due to natural diversity, some individuals had larger gametes and some had smaller gametes. Over time, it seems that the most successful matches were between a larger gamete and a smaller one. This pushed natural selection towards favoring these two sizes of gametes, and separating the world into individuals who make big gametes and those who make small ones. Essentially, it is to your benefit to do either one of two things: invest a lot of time and energy into making a few large gametes (we now these now as eggs), or invest your energy into making lots and lots of small, short lived gametes, that you can continue to make anew your whole life (we call these sperm). The smaller and more mobile and less energy intensive the better, or the larger and more stable the better. In the evolution of sexual reproduction, the middle ground falls away.
This brings us back to the original question: gender. There is then indeed a biological basis for gender. Some individuals make large gametes, the eggs or ovum. We recognize those as female. Other individuals make smaller gametes, called sperm. We recognize those as males. But that is truly a simplification. As we will discover in coming weeks, gender is truly a human construct, and as usual, nature, in its infinite intelligence, elegance and practicality has something more amazing and beautiful to show us.


Personal communication with Dr. Ann Cleveland. May 2012. Working in Academia has it advantages, including having a biologist for a boss. Over lunch, Ann enlightened me as to the origins of gender.
Sperm Biology: An Evolutionary Perspective By T. R. Birkhead, David J. Hosken, Scott Pitnick ( online exerpt, Google Books)
The origin and evolution of gamete dimorphism and the male-female phenomenon: (abstract only):