Final answer:
When using relative brain size as an indicator for intelligence, it's important to account for an organism's phylogeny because cognitive abilities might be more closely related to factors like neural density rather than just overall brain size. Researchers have revisited the encephalization quotient to develop better measures that take into account the complexity of intelligence.
Step-by-step explanation:
Accounting for phylogeny when using relative brain size as a surrogate for intelligence is important because it factors in the evolutionary history of an organism and acknowledges that cognitive abilities may not strictly depend on brain size alone. The encephalization quotient (EQ), which considers the ratio between actual brain size and expected brain size based on body size, although historically a significant measure for understanding brain evolution within the genus Homo, has been reconsidered in light of alternative approaches that suggest other aspects like cortical neuron density and neural connections might be better indicators of intelligence.
Researchers like Harry J. Jerison and teams like Schaik et al. have developed and reinvestigated formulas for EQ, proposing new methods for assessing brain size and intelligence. These approaches aim to address the issues that arise from using relative brain size, such as the exceptions in the fossil records, including Homo floresiensis, and the varying relevance of body size in cognitive performance.