The first and most obvious problem has to do with our large brains. Clearly, there is a positive selection to have a large brain because it allows room for intelligence to grow. We are the most intelligent species on the planet and we have an enormous brain for our body size. Our brain begins to grow during our development as an embryo and fetus. By the time a human is born it has an enormous brain inside its enormous head and that causes real problems during childbirth. Giving birth is always a strain on any mammal but for humans it is even more difficult because of the baby's large head. When giving birth, a woman experiences what is probably the most painful, difficult and dangerous time of her life.

A bigger birth canal is in order here but our upright posture makes the engineering impossible. A smaller head on the baby would be an answer but then the baby would have to grow its brain outside the womb in order to have a large brain. Unfortunately, growth outside the womb is not as fast or as efficient as growth in the womb. The trade off for our large brain is a painful and dangerous birth. Natural selection hasn't found a way to get around the problem.

Another, but less obvious, mistake in human evolution worth mentioning concerns our ability to speak. This is also connected to our large brain but here I would like to draw your attention to the human throat because that is how we make speech. To produce this series of complex sounds we have evolved an unusually long "windpipe" that gets in the way of the food we swallow. Sometimes, especially if we talk while eating, the apparatus in the back of our throat designed to keep air and food separate, gets confused and sends food or water into the windpipe. This causes us to cough (sometimes so violently that we propel the material out the nose). A particularly large chunk of food can become lodged in the windpipe and kill the person by suffocation.

Clearly, our large brains and speech are important to our success as a species and natural selection chose those individuals in our ancestry with large brains and long windpipes in spite of the problems. A designer should have come up with a better solution.

Some of natures "mistakes" are not so deadly but they are peculiar.

Take, for example, our sight. Here's an image of a rod - a cell in the eye that senses light.

Rhodopsin is a light sensitive chemical in the cell and it is responsible for our ability to detect light.
The cell also contains mitochondria to produce energy for the cell and a nucleus containing all the genetic materials. At the tip of the cell is a long extension called an axon and it is responsible for carrying the "message" that a photon (packet) of light has been detected by the rhodopsin.

When the message reaches the end of the axon a chemical is released and it crosses the synapse where it stimulates another nerve cell to pass the message along to the brain where it is "sensed" as light.

Millions of these rod cells and their associated nerve cells, along with the connective tissue to hold them in place, are distributed in the back of the eye in a layer called the retina.

Imagine light was coming into the eye from the left.
If you were the designer, which way would you position the cells in the retina?

Would you position them to face this way?

Would you position them to face this way?

Think like an engineer. Which way would give the rhodopsin the best exposure to the incoming light? Click on the image that you think is the best design.