A revised version of the documentary that shifts the focus away from the story of the discovery of the family and includes the views of additional scientists was shown on NOVA on 14 November 2006.
[4] Debate exists as to the nature and cause of the family's walking, including controversial speculation in the form of the Uner Tan syndrome that it may be a genetic throwback to pre-bipedal hominid locomotion.
However, Nicholas Humphrey, who accompanied the documentary makers, concluded that it was due to a rare set of genetic and developmental circumstances coming together.
Second, due to an inherited recessive genetic mutation, they have a non-progressive congenital cerebellar ataxia that impairs the balance children normally use to learn to walk bipedally.
In June 2005, Nicholas Humphrey receives a call from John Skoyles who has seen an unpublished paper by Uner Tan that focuses upon hand dominance in the family.