"it made all women in America grow to twice their original height."
All around Tom, the classroom shifted. His chair, as though under its own volition, began sliding to the left. Around him, women's desks began moving to the right. The female students' desks, chairs, and bodies began to grow as they did. Above him, the ceiling began to raise, accommodating Dr. Larson's body as she grew outwards and upwards. As the room stopped shifting, Tom looked to his right and noticed that all of the far-larger women were sitting on one side of the room, seated in desks that Tom would have had to climb into if he wanted to use them. The men, still their usual size were sitting on the other side of the room. Before him, Dr. Larson was continuing to grow alongside the chalkboard. Her lettering, once small and hard-to-read, became far vaster, though still neat. She towered above Tom. Even were Tom standing up, he was pretty sure that he'd barely come up to her hips.
Dr. Larson looked down at Tom and smiled. She seemed more confident, but he felt as though she was humoring him.
"Well, of course, that was one side effect, yes," she said. Her words echoed throughout the class. He got the feeling that she was trying to not proclaim every sentence in a booming voice. "Nuclear testing in America awakened what scientists jokingly refer to as 'the Godzilla gene,' in women. Estrogen, as it turns out, can actually facilitate greater growth under the right circumstances, such as puberty in a slightly-more radioactive America. This came along, naturally, with changes in construction to better fit the fairer--and larger--sex's new bodies." She reached out and touched the ceiling. "Can you believe that pre-1965, women's basketball games were barely-attended?" She chuckled. "I'll count that, Tom. What about some other effects?"
Tom considered, weighing his options, "Men were less likely to join professions with a lot of physical labor?"
Suddenly, new desks appeared in the room. New male students surrounded Tom, dutifully taking notes.
"Good. After all, why would a man risk themselves climbing up a ladder when a woman can just reach up and do the job without any help? Of course, mining and farming remained the same, since you can't change the size of a tunnel or a cow, but those are the exceptions to the rule. What else?"
Tom didn't like that suddenly he had to compete with more men in the dating pool. "Well, the men who were displaced from blue-collar professions tended to go into less physically-intense jobs. Some of the jobs are still blue-collar, I guess, but they're not as grueling."
The new students vanished. Tom couldn't help but wonder if there were few men in the class than before he had made his changes
"Correct again! Men who no longer were able to keep up with their female coworkers took other jobs. Machine operation is quite popular; excavators and cranes still tend to be built for men, since it requires less material to build for a smaller body. Then outside of those fields there's chefs, stenographers, and of course, the world's oldest profession."
The women on the other side of the room laughed and leered at Tom. A few waggled their eyebrows suggestively.
Dr. Larson shot the women a look. "Ladies, be respectful." She turned back to Tom. "That's good. Less than a century ago, sexual politics were far different. Women didn't feel safe around men! Can you believe that?" Tom noticed that the same lust in the students' expressions was beginning to creep into the professor's gaze. "But now of course, things have changed."
Tom suddenly felt far more vulnerable. The male students around him shifted uneasily in their chairs. It suddenly occurred to him that making sweeping supernatural changes to the past may have unintended consequences. It felt like one of those things he should have predicted.
"Anything else?" asked Dr. Larson. "What did the Growth Spurt of 1969 do?"
"Well, um..." began Tom.