Were Neanderthals smaller-brained than modern humans? Estimates of cranial capacity from fossils indicate that Neanderthals had large

Question:

Were Neanderthals smaller-brained than modern humans? Estimates of cranial capacity from fossils indicate that Neanderthals had large brains, but also that they had a large body size. The accompanying graph shows the data from Ruff et al. (1997) on estimated log-transformed brain and body sizes of Neanderthal specimens (filled circles) and early modern humans (open circles). The goal of the analysis was to determine whether humans and Neanderthals have different brain sizes once their differences in body size are taken into account.The ANOVA results of the model are listed in the following table.

Source of variation SPECIESSPECIES MASSMASS SPECIES *MASS SPECIES *MASS ResidualResidual TotalTotal Sum of

In(brain size) 7.6- 7.5- 7.4 7.3- 7.2- 7.1+ 3.9 human 4.0 o o O Neanderthal T 4.1 4.2 4.3 4.4 In(body mass)

a. Examine the ANOVA table and the graph and write the statement of the linear model that was fit to these data.

b. What does the SPECIES*MASS term represent?

c. What does the F-ratio corresponding to the SPECIES*MASS term represent?

d. What null and alternative hypotheses are tested with the SPECIES*MASS term?

e. What can you conclude from the F-ratio and P-value listed in the table for the SPECIES*MASS term?

f. In view of the goals of the study, what steps would you recommend next to test whether the brain sizes of Neanderthal and early modern humans differ after adjusting for differences in body size?

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