The Zambian Observor has an article about the Vadoma of Zimbabwe:
The Vadoma people, also known as the Bantwana tribe, which means children/descendants, are a tribe living in the north of Zimbabwe, primarily in the Urungwe and Sipolilo districts on the Zambezi river valley.
They only have two big toes on each foot.
They don’t have middle toes and the two outer ones are turned in. They still can walk but with some difficulty according to the shape, running is also difficult to them. It is said this condition helps them while climbing trees, though. The elders of the Vadoma people claim that their remote ancestors were bird like beings who came from the stars and mixed their DNA with early earth women to produce offspring. The elders state that their ancient ancestors came from the star systems of Sirius and first established colonies on a planet within our solar system that they refer to as Liitolafisi.
A substantial minority of vaDoma has a condition known as ectrodactyly in which the middle three toes are absent and the two outer ones are turned in, resulting in the tribe being known as the “two-toed” or “ostrich-footed” tribe. This is an autosomal dominant condition resulting from a single mutation on chromosome number 7. It is reported that those with the condition are not handicapped and well-integrated into the tribe. While possibly an aid in tree climbing, the condition prevails because of a small genetic pool among the vaDoma and is propagated by the tribal law that forbids members to marry outside the group.
Here, we have a "Just So" story that the Vadoma tell themselves to explain their condition, and some even claim it helps when climbing trees!
If this sounds a bit like the "Just So" story told about the Lundehund, that is exactly the point.
Just So stories refer to the children’s book by Rudyard Kipling. Killing’s stories describe how one animal or another acquires its most distinctive features, such as how the leopard got its spots, or the tiger got its stripes, or why the Cheetah always looks hungry.
In the case of polydactylism (extra toes, as in the Lundehund) or ectrodactylism (fused and distorted toes, as in the Vadoma), the cause is due to genetics. When the condition is common in a population, it is due to inbreeding.
Just So stories are a kind of Post hoc ergo propter hoc in which a reason is reverse-engineered from an observed phenomenon. I.e., if the dogs on a small and isolated island in Norway where puffins are hunted for a few weeks a year have six toes, it must be because those toes are useful to hunting puffins, and if a small and isolated tribe in Zimbabwe have only two giant toes, and occasionally climb trees, it must be because those toes are useful for climbing trees.
No and nope.
It's just bad genetics caused by inbreeding.