There are several Jacka researchers that surmise that there are different clusters of Jacka’s in England.
And that these clusters can be identified by using naming patterns and geography as defining principles to identify various Jacka family groups.
Below is an outline of naming pattern "theory"

Naming Patterns 1700-1875
The first Son was named after the father’s father
Second son named after mother’s father
Third son named after the father
Fourth son named after father’s eldest brother
First daughter named after mother’s mother
Second daughter named after father’s mother
Third daughter named after mother
Fourth daughter named after mother’s eldest sister
Exceptions to the pattern occur when the naming system produced a duplication of names.
In that case, the name was taken from the next on the list.
Another break in the pattern could be caused by a death.
If a child died in infancy, then the parents would name the subsequent new born the same name.
(Taken from: Tracing your Origins. By Angus Baxter.)

Using the International Genealogical Index (IGI) a fellow researcher has labourously extract hundreds of people with Jacka surnames (although not all) he has managed to link together various Jacka families based on the patterns occurring in their offspring’s names.

On analysis they can be divided up into different groups according to particular naming patterns and occupation types.

The five groups so far identified are:-
Lands End
Land's End (Cornish name: Pedn a Wollaz) is a headland on the Penwith peninsula, located near Penzance, Cornwall, UK.

Common thread names
Abrahams
Joseph
Hugh
Common occupation
Working the land either as labourers or farmers

Mounts Bays
Common thread names
Humphrey
Benjamin
Nicholas
And further down the descendancy the name Peter and is introduced and the name Humphrey is dropped
Common occupation
Fishermen

Redruth (group 1)
Common thread names
Richard
David
Steven
Common occupation
Miners, blacksmiths, whitesmiths, stone masons

Redruth (group 2)
Originally from Perranzubloe before moving to Redruth
Common thread names
Walter
Samuel
Common occupation - not yet identified

Scatter group
Not yet identified as a single or multiple groups with distinguishing features

Of course this is only a theory a lot more work has yet to be done such as consulitng original records etc, but perhaps eventually if we can gather enough infomration and go back far enough they will link together?

From all of this information can you identiy which group your Jacka's might belong to?

Sandra