We generally consider inheritance to flow from one generation to the next along independent lines of descent. Thus, the tree of life begins with a single root and spreads out along branches that, once separated, never rejoin. What phenomenon challenges this model of evolution?

Horizontal gene transfer

Explanation

Horizontal gene transfer refers to the movement of genetic material between multi-cellular or unicellular other than from parent to offspring.

It can happen by transduction or transformation.

The model of evolution that is based on vertical gene transfer where genes flow from one generation to the next will be challenged by the occurrence of Horizontal gene transfer,