Several tragedies mark the history of overland emigration in the American west. Perhaps the most famous of these are the outcomes of the Donner Party in 1846–1847 and of both the Willie Handcart Company and Martin Handcart Company expeditions 10 years later. In this compelling book, Donald Grayson argues that the determinants of who lived and died on the trail in these three groups can be explained by human biology. Age, sex, and family ties are the dominant biological factors. Accordingly, the highest death rates are predicted to be among the youngest and oldest members of each emigrant group, among males rather than females, and among those who traveled with smaller rather than larger kin groups. The book concludes that the patterns of mortality held in common by these three emigrant groups took place within the context of significant cultural differences and patterns of learned behavior and therefore are best explained by human biology.

The 87 members of the Donner Party experienced severe cold and starvation in the Sierra Nevada Mountains on its trip to California, and 40 people in the party died. As predicted by the biological death model, the highest death rates were among the youngest and oldest members of the party. In the age group younger than five years, 62.5% died, and in the age group of individuals greater than 40 years old, 70.0% died, significantly higher than in any other age group in the party. As predicted by the model, Donner Party males died at a higher rate than females, nearly twice as much, and sooner as well. This was expected because males die at higher rates and have lower life expectancies than females under normal conditions and because experimental studies show that the biological differences of the two sexes would intensify their mortality and longevity rates under severe cold and starvation conditions. Finally, traveling in larger families facilitated the survival of both males and females in the party.

Of an estimated 442 members of the Willie Handcart Company, 71 died from severe cold and starvation during its trip from Florence, Nebraska, to Salt Lake City. Grayson's analysis of mortality in the Willie Company found a close similarity to that of the Donner Party, even with significant differences in what the two parties experienced on the trail. The oldest age group suffered the highest death rate in the company—44% of those 40 or older died. Unlike in the Donner Party, however, the youngest age group, those under five, did not have a mortality rate higher than those under 40. Willie Handcart Company males died at a rate three times that of females in the company, similar to that of the Donner Party, and in the over 40 age group males were 10.3 times as likely to die than females. Differential mortality rates also marked the high variety of traveling kinship groups in the Willie Company, ranging from single males and females to families with single mothers, single fathers, and mother-father pairs. The highest death rates were associated with the groups that had the oldest average age. Single-mother families had the lowest death rates. In general, however, the size of the kinship group in the Willie Company does not appear to significantly increase the accuracy of mortality predictions based on age and sex.

An estimated 618 people traveled in the Martin Handcart Company, and 113 died of severe cold and starvation on its trip from Florence to Salt Lake City. As with both the Donner Party and the Willie Company, the oldest age group had the highest mortality rate—36.6% of those 40 years of age or older died in the Martin Company. As in the Willie Company but in contrast to the Donner Party, the youngest age group, those under five, had a mortality rate no higher than those under 40. The reason lies in the shorter exposure to cold and famine experienced by the Willie and Martin Companies compared with the Donner Party. Mortality rates also differed by sex in the Martin Company. Overall, males died at a rate 2.4 times greater than that of females, and male death rates were higher than female rates across all age classes. In general, sex is the only significant indicator of mortality among those under 40 years of age in the company. Finally, as with the Willie Company, the size of the kinship group in the Martin Company does not appear to significantly increase the accuracy of mortality predictions based on age and sex.

Without question, Grayson's book makes a significant contribution to our understanding of the overland emigrant experience in the American west and the context within which it took place. Historians of the American frontier and historical archaeologists will find it especially appealing. Future research on the history and archaeology of traveling emigrant parties should take this book into consideration.