The most recent common ancestor shared by all lineages in the cladogram is the number 1. Option 1 is the right choice.
In a cladogram, each branching point or node represents a divergence in evolutionary history, indicating the point where a common ancestral lineage splits into two distinct lineages.
The number assigned to each branching point typically denotes the chronological order of these events. The most recent common ancestor (MRCA) shared by all lineages in the cladogram is represented by the number at the base or origin of the diagram.
This number signifies the earliest point in evolutionary history where all the depicted lineages trace back to a single ancestral population.
Thus, by following the branches backward to their convergence point, one identifies the numerical representation of the MRCA, symbolizing the unity of those particular evolutionary lineages.
Option 1 is the right choice.