Visualisation of the birth-death algorithm from treats
Let's assume we already have a tree with three lineages after a period of t0 has elapsed (with trait values x and y at the two nodes).
Step 1: Selecting a lineage among the living lineages. For example t0 is selected. This can be controlled through the modifiers object (with selection).
Lineage selection in modifiers
"selection" part of the modifier: by default, the selection is randomly choosing one lineage among the lineages currently not extinct. In R this is equivalent to:sample(1, n)
or in the treats algorithm:sample(1, lineage$n)