Final answer:
Size and shape are not reliable indicators of relatedness due to phenomena such as convergent and divergent evolution, as well as cases where minor genetic differences can cause major morphological changes, which can misrepresent phylogenetic relationships.
Step-by-step explanation:
The statement 'size and shape are not reliable indicators of how closely different organisms are related' is supported by information that shows correlation between different characteristics is not necessarily indicative of the phylogenetic relationships among organisms. Instances of both convergent evolution and divergent evolution illustrate that organisms that appear similar (such as having the same body shape or size) may not be closely related, while organisms that are closely related may look quite different due to minor genetic changes resulting in major morphological differences.
Examples include the fact that organisms that are not separated geographically do not necessarily evolve into different species, even if they look quite different. Similarly, the case of chimpanzees and humans shows that despite sharing 99 percent of genes and originating from a common ancestor, they have considerable anatomical differences. Therefore, classification solely based on size or shape can be misleading and may not reflect the true evolutionary history of organisms.