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In Human Natures, Stanford Professor of Population Studies and Biological Sciences Paul Ehrlich delivers what readers have come to expect from him: solid, well-documented scholarship; clear, detail-filled exposition; a challenging and original point of view; provocative opinions; a warning about the perils humanity may unleash on the world; and suggestions for ways to change course before it is too late. The reading is not easy, but it is never dull, ranging from science lessons to ethical dilemmas to pointed comments about racism, creationism, and politics.
The title is deliberately plural. Though all humans share certain traits that define us as members of our species, we are individuals with widely varying natures. That fact, which makes life more difficult and interesting for everyone, is the expected result of the processes of evolution and natural selection. Our species needed a rich and varied gene pool to spread geographically and to adapt to continuous changes in environment and ecology. Biological inheritance endows each of us with possibilities, but our interactions with our environment determine which of those possibilities emerge. If the traits have survival value, the genes responsible for them are more likely to be passed to future generations.
For approximately two million years, the genus Homo has competed, cooperated, and co-evolved with innumerable species of flora and fauna. In the present epoch, we, H. sapiens, are the only surviving species of that genus, having out-competed or overwhelmed H. neanderthalensis (now believed to have been a separate species) as recently as a few tens of thousands of years ago. Though the biological evolution of our species continues slowly, with undetectable changes from one generation to the next, our remarkable brains have set us on a much more rapid evolutionary course. Each group of humans develops an evolving culture that both reflects and influences the natures of its individuals.
Unlike any other creature, we humans have shaped our environment as much as it has shaped us. First oral, then written, language enabled people to transmit technology, to communicate and store knowledge, to organize and plan, and to accelerate the process of cultural change. Now a technological "generation" may be measured in months. We are, in a sense, evolving into a new, ecology-threatening species, one that transforms the environment at a pace too fast for biological evolution to produce adaptation, yet too slow for an individual to notice without sophisticated instruments and record-keeping.
That is where both the planetary perils and Prof. Ehrlich's proposed course of action lie. We have begun to understand evolutionary theory, not just in the life sciences but also in the social sciences. It is time to apply what we know to both our technologies and our cultures. We must use them both to create a sustainable world. The human prospect depends not only on the genes that shape our bodies, but also on the human natures that shape our cultures.