This is by no means a scientifically accurate article. These are my thoughts, and I'd be happy to discuss this topic. Take it with a grain of salt.
Evolution builds upon natural selection. With every generation of a species, there is a slight chance of mutation, possibly giving an individual advantages or disadvantages in the ability to survive and give offspring. Somewhere way up in our evolutionary tree, a microbe might have mutated a gene that allowed it expand and retract a part of its body. As it turns out, this proves useful in fleeing from predators, while other individuals of this species might fall prey on their first day. The microbe has a slightly larger chance to survive and give offspring. On the other hand, mutations might also result in a fatal illness (cancer, in other words). Oftentimes, this individual does not survive long enough to give offspring.
150 years ago, giving birth was literally an act of life and death. Many children died at a young age. They were not tough enough from an evolutionary standpoint, and were therefore "filtered" out by natural selection. Only the strongest survived and gave offspring.
Todays medicine is (fortunately!) very powerful. Very few children die at birth and a lot less people are dying from an illness like the flu. This is an evolutionary anomaly. Natural selection has been defeated to a certain degree. We don't need to run from predators anymore and are less prone to desease. Every one of us is more or less equally able to give offspring. We can't really gain an advantage over others anymore. We are not evolving.
This is post 002 of #100DaysToOffload.