http://www.moggies.co.uk/moggies.html:

"Most authorities believe that the shorthaired breeds of domestic cat
are derived from the Cafra cat, Felis Lybica Cafra, a species of African
wildcat domesticated by the ancient Egyptians perhaps as early as 2500
BC and transported by the Crusaders to Europe, where it interbred with
the indigenous smaller wildcats. The longhaired breeds may have sprung
from the Asian wildcat, Felis manul. Over the centuries, domestic cats
have remained virtually the same size, weighing about 8lb (3.6kg) when
fully grown."

Cheers

katysails wrote:

MC asked: How big should Felix Domesticus be?

You should be able to stuff it in a breadbox.