Slips have nothing to do with "knowing how to walk". Slips can and do lead to serious injury. This has been studied empirically and objectively.
For 2006, the National Safety Council reported that unintentional injury led to over 27 million visits to emergency rooms. Typically, falls lead all other causes of ER visits. In 2007, falls led to the death of 21,600 Americans
. In fact, the number of deaths (and the death rate) due to unintentional injury have been increasing for several years. [NSC 2008 "Report..."]
Slips are primarily caused by a slippery surface and compounded by wearing the wrong footwear. In normal walking, two types of slips occur. The first of these occurs as the heel of the forward foot contacts the walking surface. Then, the front foot slips forward, and the person falls backward.
The second type of fall occurs when the rear foot slips backward. The force to move forward is on the sole of the rear foot. As the rear heal is lifted and the force moves forward to the front of the sole, the foot slips back and the person falls.
To prevent slips and falls, a high coefficient of friction (COF) between the shoe and walking surface is needed (Figure 1). On icy, wet, and oily surfaces, the COF can be as low as 0.10 with shoes that are not slip resistant. A COF of 0.40 to 0.50 or more is needed for excellent traction.
To put these figures in perspective, a brushed concrete surface and a rubber heel will often show a COF greater than 1.0. Leather soles on a wet smooth surface, such as ceramic tile or ice, may have a COF as low as 0.10
I'll leave it to those who are interested to do their own research into COF (coefficient of friction).
On the topic of being a "googlewonk" or an armchair physicist, I formally studied general and organic chemistry, then material science. My prior career was as a rare book conservator, and I have extensive study and experience with the chemistry and physical properties of paper and leather. I've worked on leather that is over 1000 years old. Not shoes mind you. I claim no special knowledge of shoes.
I respect the opinions and experience of at least some of the people who post here. Particularly, I respect the experience of DWFII, I find his posts generally informative and interesting. But in some cases he is simply drawing incorrect conclusions.
I entirely agree with apropos' conclusions.