The brother of the murdered man must engage the murderer; but any one on either side who might care to join in the fray was at liberty to do so.

Hence it is but a step to the formal duel, as found, for instance, amongst the Apaches of North America.
Now the legal duel is an advance on the collective bear-fight, if only because it brings home to the individual perpetrator of the crime that he will have to answer for it.

Cranz, the great authority on the Eskimo of Greenland, naively remarks that a Greenlander dare not murder or otherwise wrong another, since it might possibly cost him the life of his best friend.

Did the Greenlander know that it would probably cost him his own life, his sense of responsibility, we may surmise, might be somewhat quickened.

On the other hand, duelling is not a satisfactory way of redressing the balance, since it merely gives the powerful bully an opportunity of adding a second murder to the first.
Hence the ordeal marks an advance in legal evolution.