This August, the National Institutes of Health announced that it was considering funding research that involves the creation of human/nonhuman chimeras through the introduction of human pluripotent cells into nonhuman vertebrate embryos. I happened to be teaching about the ethics of human embryonic stem-cell research at the time, and given that the NIH was seeking public comment on this proposed research, I asked my students to write papers commenting on it. Although I provided the class with scientific literature that dispels concerns about this research leading to creatures of the sort found in Greek mythology, my students seemed haunted by what might emerge from the lab of a latter-day Frankenstein. Alas, the cloned monstrosities conjured by my students (and most critics of biotechnology) are matched only by the absurdly utopian visions of transhumanists, who long for a post-human future. Both groups should be required to read Scott Solomon’s Future Humans.
One problem with both utopian and dystopian visions about the future of humanity is that they can lead us to ignore serious scientific questions about whether humans continue to evolve and, if so, toward what. It is thus a tonic to find a book like Future Humans that takes a sober look at the scientific evidence supporting the claim that humans are continuously evolving and might one day evolve into a different species.
Two sentences from the final chapter of Future Humans tell you a lot about this book. “So far,” Solomon writes, “our discussion has mostly looked into our relative short-term future—the next thousand generations or so.” “What,” he continues “are the long-term prospects for our species?” When an author seeks to summarize the likely evolutionary trajectory of humanity and defines the “near-term” of that trajectory as a thousand generations, you know both that the work is ambitious and that you shouldn’t expect much in the way of detail about that near-term future, much less about the long-term one.
Nevertheless, Solomon’s review of the scientific literature he believes to be most relevant to assessing the likely evolutionary future of humanity is lively and thought-provoking. This literature encompasses a wide range of disciplines, including paleoanthropology, molecular genetics, microbiology, evolutionary psychology, demography, and evolutionary biology. No one scientist can be an expert in all these disciplines, but Solomon’s ability to explain complicated science from a variety of fields is impressive.
One technique for engaging a general audience in the details of esoteric science is to describe the scientist behind the science, and Solomon uses this technique to good effect throughout. For example, the book opens with a vivid description of Pardis Sabeti, an academic superstar whose work includes the development of a mathematical model for analyzing gene-sequence data that allows researchers to determine whether natural selection for certain gene variations is recent or ancient. Solomon’s account of Sabeti’s work is clear, and it is hard not to be interested when you hear her credentials. She was a National Merit Scholar at MIT, a Rhodes scholar at Oxford, and only the third woman ever to graduate from Harvard Medical School summa cum laude.
Sabeti’s work on the role of malaria as an agent of natural selection in humans, and her research on Lassa hemorrhagic fever in West Africa led her to a place on the front lines of the Ebola outbreak in May 2014. By August of that year, Sabeti and her colleagues had published the results of their analysis on ninety-nine Ebola genomes her team had collected from seventy-eight different victims. By the time of publication, five of Sabeti’s coauthors had died from the virus. Hearing about Sabeti’s work on the genetic analysis of malaria, hemorrhagic fever, and Ebola, it is hard to dispute Solomon’s claim that infectious diseases have been among the most important influences on our evolutionary history and will likely continue to be so.
Of course, not all the relevant science involves a life-and-death struggle against infectious disease, and Solomon also skillfully walks us through the prosaic work of demographers who have documented natural selection at work in local and isolated communities. For example, Solomon introduces us to the geneticist Emmanuel Milot, who scoured the archives of the Canadian Catholic Church in Quebec City to document natural selection among isolated groups for whom detailed population records were available across several generations. He found the records of one such group in church records for residents of Ile-aux-Coudres, an island off the Saint Lawrence River.
In reviewing these records, Milot noticed that in just a few generations—those living between 1800 and 1939—the average age at which women became mothers dropped from twenty-six to twenty-two. Through a painstaking review of the records and a statistical analysis of these data, Milot was able to determine that this shift was unlikely to have been caused by changes in health, cultural practices, or genetic drift. Instead, the best explanation appears to be natural selection.
If using church records as a tool for documenting natural selection would strike many as surprising, it shouldn’t. Indeed, it was first suggested by an Italian priest, Antonio Moroni, in 1951 to the population geneticist and member of the Pontifical Academy of Sciences, Luigi Luca Cavalli-Sforza, who then used church records to examine how marriages between relatives affected the distribution of particular genes throughout Italy. Using the rich demographic resource of church records, Cavalli-Sforza and Moroni were able to map genetic drift in all of Italy and to provide a model for understanding the genetic effects of drift and inbreeding.
There are numerous stories like those of Sabeti, Milot, and Cavalli-Sforza in Future Humans, and learning the science behind the stories makes the book both enjoyable and worthwhile. It is also generally serious and sober, as a book on this topic ought to be. Still, there are points at which Solomon seems unable to resist the sort of flights of fancy that I complained about at the start. The chapter on genetic selection and “sperm wars” strikes me as wildly speculative, and the book ends with an odd discussion about humans colonizing Mars. Strangely, Solomon wonders whether the Mars colonists might not be the new species toward which we are evolving. These aberrations aside, Future Humans is well worth reading.