A study reported in Nature claims that women who give birth later in life tend to live longer. Of the 78 women who were at least 100 years old at the time of the study, 19% had given birth after their 40th birthday. Of the 54 women who were 73 years old at the time of the study, only 5.5% had given birth after their 40th birthday. A researcher stated that "if your reproductive system is aging slowly enough that you can have a child in your 40s, it probably bodes well for the fact that the rest of you is aging slowly too." Was this an observational study or an experiment? Does the study suggest that later child bearing causes longer lifetimes or that later child bearing reflects an underlying cause? Comment on how persuasive you find the conclusions of the report.