Because "descendant" means their children, grandchildren, great grandchildren, etc. And not just THEIR kids alone.
1. :kitty: - :kitty:
2. :kitty: - :kitty: - :kitty: - :kitty: <-- Children
3. :kitty: (x4-6 babies) :kitty: (x4-6) :kitty: (x4-6) :kitty: (x4-6) <-- GrandChildren
4. :kitty: (x4-6)(x4-6) :kitty: (x4-6)(x4-6) :kitty: (x4-6)(x4-6) :kitty: (x4-6)(x4-6) <-- Great Grandchildren
1. Mom and Dad
2. Mom and Dad have 4-6 babies. Which are their children.
3. Then each one of their children having 4-6 babies. Which would be their Grandchildren.
4. Then each grandchild having 4-6 babies and then those 4-6 babies having their own 4-6 babies. Which would be their Great Grandchildren.
But I don't know if that would equal 2000 descendants in 18 months. I guess I could try the math but I don't want to unless I know that grandchildren and great grandchildren count?
LOL I don't even know if the shit I just typed makes any sense.

FUCK MATH.