In this wide-ranging survey of what it is that has made and that continues to make us human, Ehrlich touches on a number of themes--among them, his recurrent observation that science has taught us little about how genes influence human behaviour. (Instead, he notes wryly, "science tells us that we are creatures of accident clinging to a ball of mud hurtling aimlessly through space. This is not a notion to warm hearts or rouse multitudes.") He urges that scientists take a larger, interdisciplinary view that looks beyond mere genetics to the larger forces that shape our lives, a view for which Human Natures makes a handy, and highly accessible, primer. --Gregory McNamee

"Human nature" is often cited as a foundation for many behavioural traits. The fallacy of that moral expression is revealed in the variety of our habits. Ehrlich recognises that variation in his title and goes on to explain it in this book. While the genetic foundation of our behaviour is being solidly established by much field research, he ultimately concludes much of that basis is overriden by our cultural influences. Much of our confusion about "nature versus nurture", he contends, lies in the rapid pace of humanity. Compared to most other species, our mental development raced past the other animals - with language as the accelerator pedal. Since the genetic base for most traits is so slow and nearly muted, our development agriculture, religion and urban society virtually overwhelmed our "animal instincts". The prime example, of course, is the massive impact we have on our environment.

Ehrlich's key in assessing genetic versus cultural input lies [logically!] in the structure of the brain. When he wrote this book, the human genome was thought to be comprised of 100 000 genes. With that figure halved, he concludes the genome hasn't the power to command the billions of neurons with their trillions of connections that comprise the human brain. This "gene" shortage, he avers, suggests the genome hasn't the capacity to drive human behaviour to any significant degree. This rather simplisitic enumeration ignores the fact that the entire genome, whatever the number of genes, must be highly interactive in many areas of the body - the brain is simply another part of the mechanism. He is apparently unaware of the brain research showing how similar interactions have been mapped within the brain. Genes merely kickstart the process, they don't need to "control" our behaviour.

Ehrlich takes the usual swipes at Richard Dawkins as he builds his narrative. Like so many others, Ehrlich's reading of "The Selfish Gene" appears to have ceased at the title. To him, the "Great Leap Forward" of some fifty thousand years ago emancipated us from the shackles of our genetic heritage. With the development of language [which wouldn't have happened without a biologically endowed "voice box"], human cognition, hence behaviour, launched on a new course. Ehrlich asserts we've never looked back, but also warns our capabilities should be adapted to now look forward. Our abilities threaten the biosphere with an intensity and scope no other species possessed.

In his conclusion, the author nearly reverses all his prior narrative. He urges humanity to develop a better understanding of its place within nature. That, of course, means a full programme of understanding animal behaviour and the mechanisms animals and plants use to stay alive and reproduce. Our evolution, particularly the cultural input, has led us to believe we are distinct from Nature. Ehrlich recognises the dangers of such an attitude and urges us to overcome it. Although an excellent synthesis and supremely comprehensive, it's unfortunate that Ehrlich's prejudices blinded him to create a problem that doesn't exist. Nobody argues for "biological determinism" in an absolute sense - certainly not Dawkins. Where Ehrlich is correct is that we must increase our knowledge of how nature works and undertake the tasks needed to stop and reverse the spoilage under way. [stephen a. haines - Ottawa, Canada]