I Am Sure Someone Answered This in a Comment in the Last Few Years

But blogger lets me search posts, not comments.  There is a sci-fi story where a scientist demonstrates to his class that time is actually quite resilient to changes in the past.  He starts a pendulum swinging  through a time portal.  The first swing kills a bug, which causes the ancestor of an early mammal to starve, removing a useful mutation from the gene pool.  It is a short story, but it adequately demonstrates the long-term effects, with each swing slowly altering the classroom and its inhabitants.  At the end, the professor and his students are now reptilian, not primates, and he croaks, "See!  Nothing has changed!"  Author, title?  "Anyone, anyone."