The random ahnentafel numbers make it clear that these "foreign" trees haven't been built the hard way. There is obviously some means of cobbling together different ancestry trees with minimal clicks/keystrokes. I've taken an Ancestry DNA test and it seems thrulines may be how it happens. Click on any ancestor with matches on the thrulines page, if in the Relationships (tree view) tab there are individuals in green with "evaluate" against them, a few more clicks seems to be all it takes to add entire branches.
Jane :-)
The green "potential ancestors" that appear, with Thrulines but also if you have a parentless individual in your tree is definitely how much of this happens. Also Ancestry used to provide in hints to three other trees at a time with trees that have the same person in their tree, and it took a couple of clicks to link everyone. Now it's just one tree. I suspect many do not notice is the green EVALUATE button next to the potential ancestor in Thrulines.
Most of my trees are private including a large (30,000+) quick and dirty tree for when I'm playing around with ideas and still searching. I became very frustrated with incorrect info about one set of ancestors (in the 1970s was printed and distributed at a family reunion) that I have made that tree public with images from parish records, newspapers etc. I regularly make contact with the incorrect info based on the 1970s info and send them a link to the tree (as many do not have a sub). It's slow work.... Five years on from working out who were the correct parents of my Scottish gtgtgtgt-grandmother was there are still numerous trees that show her from Alloa, not Fife, and with the wrong parents. And Ancestry brings up the wrong parents (in green) for her.