They do. Evolution.<p>They needed to evolve to reach a certain age ( -&gt; once they cant reproduce anymore) without dying to cancer.
<a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=fMMPKJFYzdY" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=fMMPKJFYzdY</a> for a more in depth explaination