Noonan et al. (2006) used DNA sequence data and the method of maximum likelihood to add the extinct Neanderthal species to the tree of humans and other apes (see Figure 20.2- 1). The accompanying graph is a likelihood curve for the time of the split between humans and Neanderthals, which is more recent than that between humans and the other living apes.

Figure 20.2- 1

a. What does the likelihood curve measure in this example?

b. With the aid of a ruler, use the likelihood curve to find the maximum likelihood estimate of divergence time.

c. Using this same curve, approximate the likelihood-based 95% confidence interval for divergence time.

d. What does the interval in part (c) measure? Explain.