But he is MY 3xgreat grandfather

Family historians take a proprietary interest in their ancestors. We tend to cling to them like we do our children. (Perhaps even more than to our children, since ancestors show little inclination to move out!)

While there can be no doubt that it is MY family tree that I am constructing, it is not reasonable to claim "ownership" over every person in it.

The following model shows five generations in which each descendent of the patriarch has between zero and three children. Even with these conservative assumptions, the highlighted family historian has 18 others in her generation with equal claim on the ancestor in question. Allow larger families or extend back more generations and the number of claimants grows rapidly.

Fortunately not all of these people will be interested in genealogy, but it is very likely that there is someone else whose research will overlap yours — with the potential for cooperation or conflict.

In recent years, the philosophy underpinning on-line tree building (such as the Ancestry model) has been to let a thousand flowers bloom. We each constructed our own project and the host provided "hints" where it seemed that the same individual was also in another tree. Each user was free to "borrow" information from others, but the products of their work remained separate.

The Family Search organisation (owned by the Church of the Latter-day Saints) has recognised that there are not multiple instances of Great Uncle George sitting in dozens of different trees — just one person with connections to many others through different parts of a single large tree.

Forest or family tree?

Their new Family Tree facility allows (even requires) all researchers to share their common ancestors and to contribute their individual pieces of information to a shared understanding.

The logic behind this is impeccable. Family history ought to be a collaborative activity. I understand the need for this position and support the principle whole-heartedly. Now let's wait to see how I react the first time that someone changes something with respect to one of MY ancestors.