[jennyp]

And the sample is how many?

That information is restricted to the small, privileged subset of people who read the article. :-)

The findings, published today by Dr Caspari and Dr Sang-Hee Lee in the Proceedings of the National Academy of Sciences, were based on a comparison of more than 750 tooth fossils from successive time periods.

[Lester Moore]

My eyes saw but my mind did not perceive. Thanks.

I suspected a rather small sample and 750 tooth fossils from successive time periods is small.