This is a kind of evolution which must be a rare event.

This is a rare event in my line of work.

"But I have to say that it is still a rare event."

The baby was raised by its own mother, which remains a rare event.

It is often used in the study of rare events.

It's just one of those rare events you're really not prepared for.

This rare event will be very difficult to observe from Earth.

I didn't need anyone to tell me that this was a rare event.

It is a rare event in my life, but we are not at a fun fair here.

But rare events in a large group can still mean many people will be affected.