the last 20 generations, since the start of human habitation there. As expected, the residents of the Island of Santiago, where malaria is most prevalent, show the highest prevalence of resistance. This is one of the most rapid cases of change to the human genome measured. Geneticist Steve Jones told the BBC that during the sixteenth century, only a third of English babies survived until the age of 21, compared to 99% in the twenty-first century. Medical advances, especially those made in the twentieth century, made this change possible. Yet while people from the developed world today are living longer and healthier lives, many are choosing to have just a few or no children at all, meaning evolutionary forces continue to act on the human gene pool, just in a different way. While modern medicine appears to shield humanity from the pressures of natural selection, it does not prevent other evolutionary processes from taking place. According to neutral selection theory, natural selection affects only 8% of the human genome, meaning mutations in the remaining parts of the genome can change their frequency by pure chance. If natural selective pressures are reduced, then traits that are normally purged are not removed as quickly, which could increase their frequency and speed up evolution. There is evidence that the rate of human mutation is rising. For humans, the largest source of heritable mutations is sperm; a man accumulates more and more mutations in his sperm as he ages. Hence, men delaying reproduction can affect human evolution. The accumulation of so many mutations in a short period of time could pose genetic problems for future human generations. A 2012 study led by Augustin Kong suggests that the number of de novo (new) mutations increases by about two per year of delayed reproduction by the father and that the total number of paternal mutations doubles every 16.5 years. Dependence on modern medicine itself is another evolutionary time bomb. For a long time, it has reduced the fatality of genetic defects and contagious diseases, allowing more and more humans to survive and reproduce, but it has also enabled maladaptive traits that would otherwise be culled to accumulate in the gene pool. This is not a problem as long as access to modern healthcare is maintained. But natural selective pressures will mount considerably if that is taken away. Nevertheless, dependence on medicine rather than genetic adaptations will