Book Review: The Invisible History of the Human Race

In The Invisible History of the Human Race (Viking, The Penguin Group), Dr. Christine Kenneally asks, “How does human history jive with genomics?” and “What would explain inconsistencies?”

Within the first 10 pages, Dr. Kenneally points out that even if one could possibly recreate a particular genome, one could not precisely replicate the conditions of its creation and even less so its expression, since over time genes respond differently to their environment. This is true even for identical twins.

Kenneally traces and explains how DNA strongly influences who we are and, to a lesser extent, how we behave. She starts with an explanation of “path dependency,” which shows how events are connected in a timeline. From any particular node, there may be several possible developmental paths. Retrospective viewing of the interconnections shows the trail and timeline measured in generations. Our DNA code is mingled at every generation according to scripts associated with fertilization and cell division. These scripts are subject to variable execution and also to epigenetic factors such as natural selection, which gradually influence differences among individuals across generations.

About half of the book is devoted to a description of the genealogy of humans, in which Kenneally correlates human evolution with historical events. For example, The Y chromosome is passed nearly intact from father to son. About 1000 years ago, the Y chromosomes of many Asian ancestry groups were terminated and replaced by a distinctive Y chromosome that Kenneally traces back to Genghis Khan, apparently as a result of a Mongol invasion.

Other bottlenecks in genomics that are cited include the migration of humanoids out of Africa 60,000 years ago. The migrants broke into groups that became isolated in various locations. Over time, this isolation led to a decrease in genetic diversity and an increase in deleterious mutations.

How genes change—or are changed by—social organization is the primary topic for much of the latter half of the book. Kenneally argues that genetics play a minimal role in the social behavior of groups, contradicting the thought process that leads some people to racist beliefs. Indeed, the correlation of genes of particular groups with social behavior such as criminality is very weak. For example, the author contrasts the low crime rate in Hobart, Tasmania, which was populated by prisoners of Mother England, with criminality in Mother England, where crime rates were higher, to show that the environment had more to do with the group behaving criminally than did any genetic predisposition.

In The Invisible History of the Human Race, Keneally uses the word “race” to denote humans. She strongly objects when people try to differentiate various ancestry groups by this metric, contending that ancestry, which is very much determined by the fact that people mate with others in their proximity, is a much more telling factor for human genomic development.

Current influences on behavior and subsequently on genetics that are not discussed include global mobility of higher business and economic classes and the forced migration with lands and across borders by those seeking to avoid poverty, famine, war and other dislocating events.

As scientists, we are often asked to comment on genetics and its relationship to current public issues. Kenneally’s thoughtful consideration and detailed investigation provide a greater understanding of the positive and negative aspects of evolution as guided by DNA. It becomes clear that it is important to consider path dependency coupled with details of DNA biochemistry to help explain the process of evolving life. Each of us is a unique brick in a very long evolutionary road.

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