Final answer:
Phylogenetic trees display evolutionary relationships where closeness on the tree indicates more recent common ancestry. They are constructed using homologous characteristics, but their representation may change with new evidence like genetic data. Cladograms help clarify evolutionary ties, and evolutionary relationships are often more complex than simple physical resemblance.
Step-by-step explanation:
When discussing organisms that are all very closely related with regards to phylogeny, we are primarily concerned with how recent the common ancestry is shared among them. A phylogenetic tree is a diagram that represents the evolutionary relationships between different species - the closer two species are on the tree, the more recent their common ancestor. For example, if Species 1 and Species 2 share a more recent ancestor with each other than either does with Species 3, they would be considered to be more closely related evolutionarily. This is illustrated by their positions on the phylogenetic tree.
Common relatedness can be determined by various factors such as homologous DNA sequences, which provide evidence of a shared evolutionary past. Homologous traits indicate that species have derived from a common ancestor, and such traits are used to construct cladograms as part of the phylogenetic analysis. However, not all organisms that appear similar are closely related - this is often the result of convergent evolution where analogous traits evolve independently in different lineages under similar environmental pressures.
It's important to note that phylogenetic trees are not static; they are hypotheses that are regularly revised with new genetic and morphological data. Consequently, the relationships depicted in phylogenetic trees are subject to change as researchers update the trees in light of new evidence. For instance, despite their physical appearance, recent genetic studies have shown that the closest living relative of the whale is the hippopotamus, not the visually similar pig.