Final answer:
To prove that two species are closely related, scientists primarily analyze DNA sequences, as this provides the strongest evidence for common ancestry. Homologous structures also contribute to understanding relatedness, but morphologic traits like tail length are less informative. Phylogenetic trees like cladograms illustrate these evolutionary relationships.
Step-by-step explanation:
To demonstrate that two species are closely related, a scientist can use various methods, with analyzing DNA sequences being one of the most definitive. DNA comparisons reveal the extent of shared genetic material, and a higher degree of similarity often indicates a closer evolutionary relationship. This can be done using tools such as BLAST to compare genes and construct a cladogram, which is a diagram showing the phylogenetic relationships amongst species.
In addition to DNA, scientists consider homologous structures, which are physical features that are similar due to evolutionary history rather than convergent evolution. These can include similarities in skeletal structures, like the arrangement of bones in the limbs of different animals. Scientists also study the geographical distribution of species to understand historical habitats and potential for gene flow between populations. However, some attributes like the number of offspring or the length of their tails are less reliable as these can be subject to environmental influences and do not necessarily reflect genetic relatedness.
Therefore, for accurate phylogenetic analysis, morphologic and genetic data are both crucial, though genetic data typically provide more concrete evidence of relatedness. Molecular comparisons and the construction of phylogenetic trees, such as cladograms, are central to understanding evolutionary relationships.