tense problem

[Swordfish117]

Although all dogs are descended from the wolf and the jackel, the various breeds of dog are so different from one another that it hardly seems possible that they had a common ancestry.

Is this sentence correct ?
Dont you think that the usage of 'had' has a wrong tense.
Instead it should be 'have'.

Also what is the difference between
'one another' and 'each other'
In my opinion...
One another is used when there are more than two people/animals etc.
Each other is used when he comparision is between 2.

[Pamela]