Natural selection is not going to smooth the edges of our anatomical imperfections if those features play little to no role in who lives and who dies and how we choose our mates. In addition, there is no stopping new mutations from cropping up in the human genome. Some mutations do lead to improvements, but most genetic mutations either cause no effect or have a deleterious outcome. Whereas natural selection may have previously filtered out mutations with a negative impact on our anatomical features, in the more modern scenario many of those mutations persist within the genome.
