124 Will Robots Inherit the Earth? HEALTH AND LONGEVITY Such a future cannot be realized through biology. In recent times we have learned a lot about health and how to main- tain it. We have devised thousands of specific treatments for particular diseases and disabilities. Scientists are seriously con- sidering  the  possibility  of  extending  the  maximum  human life span, but we have not yet achieved this goal. According to  the  estimates  of  Roy  Walford,  professor  of  pathology  at UCLA Medical School, the average human life span was about 22 years in ancient Rome; about 50 in the developed countries in 1900, and today stands at about 75. Still, each of those curves seems to terminate near 115 years [1]. Centuries of improve- ments in health care have had no effect on that maximum. Why are our life spans so limited? The answer is simple: Natural  selection  favors  the  genes  of  those  with  the  most descendants. Those numbers tend to grow exponentially with the  number  of  generations.  This  favors  the  genes  of  those who  reproduce  at  earlier  ages.  Evolution  does  not  usually favor  genes  that  lengthen  lives  beyond  that  amount  adults need to care for their young. Indeed, it may even favor off- spring who do not have to compete with living parents. Such competition could promote the accumulation of genes that cause death. We humans appear to be the longest-lived warm- blooded animals. What selective pressure might have led to our present longevity, almost twice that of our other primate relatives? This is related to wisdom! Among all mammals, our infants are the most poorly equipped to survive by themselves. Perhaps we needed not only parents, but grandparents too, to care for us and to pass on precious survival tips. Even with such advice, there are many causes of mortality to which we might succumb. Some deaths result from infections. Our immune systems have evolved versatile ways to deal with most diseases. Unhappily though, those very same immune