As human brains continue to evolve, will humans eventually develop gigantic heads and scrawny bodies, as depicted in some sci-fi films? Historically, the birthing process has limited brain size, because babies’ heads had to fit through the birth canal.

Today, however, Caesarian sections circumvent that process. As many as 46 percent of babies born today in China are delivered via C-section, Pobiner said. With advances in fertility and better postnatal medical care, she asked, “Are we screwing with natural selection?”

The world population is growing, and a bigger population also evolves faster, Pobiner said. But, with rising sea levels and less land available, waterborne and airborne illness could spread more easily, Pobiner said.