[supercat]

The birthrate is given as births/animal/decade. The deathrate is deaths/animal/decade. birthrate = deathrate What's contradictory?

Birth rate is stated as 5 per animal per decade. Death rate is one per animal per decade. Birthrate is not equal to death rate, even though a stable population would require it to be so.

[spunkets]

"Death rate is one per animal per decade."

The avg lifespan is 10 years. Since there are 5 born per decade, 5 die per decade. The population just didn't pop up and start all in phase, it contains animals of all ages.