Archeologists dig all over the earth to find the history of people who existed too early to leave a written history. There is a new sort of archeology, however, that is changing our long-range view of human pre-history. Scientists are digging into cells, into the genes that everyone knows make us what we are. The details from this new research have given revolutionary insight into where humans came from, how they spread, and the origin and superficiality of races. In _The Journey of Man_ (Princeton University Press), Spencer Wells, a population geneticist, has written a wonderfully clear book of origins, drawing upon not just genes but history, geography, archeology, and linguistics.
In part, the book is a summary of refutations against the ideas of anthropologists who maintained that different races were subspecies that arose in different regions at different times. No such hypotheses could be tested in the time they were issued, and now they can. DNA in the cells from mitochondria, and the DNA in the male Y chromosome do not shuffle the way ordinary chromosomes do, and thus are very stable from one generation to the next. Mutations happen, and accumulate, and may be used to see how closely related humans from different regions of the world are. The genetic results of both mitochondrial and Y chromosome research confirm each other, and are unambiguous. We are all out of Africa. We stayed in Africa as humans for generations, and almost all the genetic variation we were going to get was within us at that time. Then around 40,000 years ago, propelled perhaps because of weather changes, we started our travels. _Journey_ has good diagrams, but a map showing the flow of different Y chromosome linkages around the world can be regarded with awe, for the history it shows and for the scientific advances that have made such a diagram possible.
Our current way of living has wrought changes in plenty of the subjects in this book. The trail of languages in many ways parallels the trail of genes around the world, but as we develop a global culture, languages are dying out at a faster rate than ever before. Also, there is greater mixing of genes from different cultures now that easy travel makes possible the meeting of members of tribes that would never have met before. It could be that we have passed the heyday for the sort of research reported here, as populations swap genes in unprecedented ways. Nonetheless, Wells's book is full of enthusiasm for basic research, and the results described here are fascinating. We can look back at our origins with new respect for how long and how strange a journey it has been, and with the increasing realization that that our one species has one shared history.