The Verreaux's sifaka mates for life. The difference genetically between this sifaka and another which is not monogamous must be a small fraction of a percent. This could be studied and you would find the gene for monogamy. Or is it nurture? Or some other form of memory which we have not discovered yet. Today we saw this sifaka dance for about 100 meters. Previously we had only seen a few steps at a time.
The indri can apparently jump 10 meters from one tree to another. We did not see such a leap, but we did see one make a series of 5/6 meter jumps from trunk to trunk through the forest until he disappeared from sight. The speed was amazing. When you see them hanging from a limb you realize how they manage this. They have extremely powerful bodies. The female is the largest and when walking on the forest floor ambles upright like a human.