Hi..

The lions were MUCH bigger than the average African lion. The reason for this tying up with the fact that did not have manes..
The mane-less lion is NOT only found in Tsavo, and it is not a genetic problem. Note that during the attacks in Tsavo, there was a great famine, lots of dead animals. That caused the lion population to kull (killing off members of a herd or pride so that here is enough food for the rest).. in a way.. because of these reasons the lions were STERILE!! So the growth hormones took over. Much like a body builder on steroids..

I saw a mane-less lion in South Affrica, next to the Kruger park.. He is HUGE.. has no mane, and is also sterile (made so by a zoo owner at birth)