We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample , constraining the birth properties , beaming and evolution of these spin-powered objects .
Using quantitative tests of agreement with the distributions of observed spin and pulse properties , we find that short birth periods P _ { 0 } \approx 50 ms and \gamma -ray beams arising in the outer magnetosphere , dominated by a single pole , are strongly preferred .
The modeled relative numbers of radio-detected and radio-quiet objects agrees well with the data .
Although the sample is local , extrapolation to the full Galaxy implies a \gamma -ray pulsar birthrate 1/ ( 59 yr ) .
This is shown to be in good agreement with the estimated Galactic core collapse rate and with the local density of OB star progenitors .
We give predictions for the numbers of expected young pulsar detections if Fermi LAT observations continue 10 years .
In contrast to the potentially significant contribution of unresolved millisecond pulsars , we find that young pulsars should contribute little to the Galactic \gamma -ray background .