Why Humans are Different -- Oy Vey!

11/16/2007 06:14 pm ET | Updated May 25, 2011

How do we talk about human differences in a society that believes that "diversity" should be celebrated, but only if it's skin deep?

That conundrum has been on my mind because of the intense personal reaction that's bubbled to the surface in the weeks since my new book, Abraham's Children: Race, Identity and the DNA of the Chosen People, was released. The narrative arc of the book highlights the remarkable new insights gleaned from DNA research about our shared Israelite ancestry -- genetic markers that help all of us trace our personal stories back in time and illuminating the hidden history of the Bible. DNA sheds light on numerous mysteries, including the story of Moses and Aaron; the fate of the Lost Tribes; the impact of Jesus in establishing a new course in religion by moving away from tribal connections and ancestry to faith; the origins of Ashkenazi (European) Jewry; and the role of DNA in shaping religious and Western identity in Jews and Christians.

But the sub-text of the book is what has caught some people's attention. I explore what we popularly refer to as "race" but what scientists call "populations." In 2001, when the early sketch of the human genome was unveiled, President Clinton declared that we were more than 99 percent genetically similar. It was a kum-ba-ya moment, but it did not reflect a nuanced scientific perspective on human biodiversity.

In the last few years, we've entered a more precarious era of scientific research. We've been able to map the entire human genome and examine chunks of DNA, known as haplotypes, and what they tell us starkly challenges conventional wisdom. These genetic blocks have been linked to a variety of disease and other human characteristics, including behaviors, in specific populations that some scientists had believed were spread evenly across all groups.

One of the world's most interesting subpopulations, at least to geneticists, is the Jews. Over the course of Ashkenazi history, the rate of non-Jewish lineages that have slipped into the Jewish gene pool, per generation, is estimated at 0.5 percent -- the lowest known rate of paternity certainty of any identifiable population -- a remarkable testimony if not necessarily to spousal loyalty than to Jewish fidelity. Jews are not a "race" -- the word carries the historical baggage of pseudo-science, which is why scientists shy away from using it -- but they do share distinct characteristics, such as a susceptibility to certain diseases.

The net is that we are not just one human family with superficial differences. While reflective of a common genetic blueprint, human evolution is remarkably regionalized with meaningful differences showing up from ancestral population to ancestral population. Said another way: humans spread globally and evolved locally. Scientists are gradually identifying population differences -- hard-wired -- in each population's ability to taste, smell, digest, in bone structure, physiological capacities -- and yes, even brain function. Abraham's Children addresses, on its discussion of the history of the "Jewish race" -- that's how Jews were commonly referred to until World War II -- and the debate over Jewish IQ, which has received (to my chagrin) the most attention in the media.

This new focus of human genome research poses a social challenge for all of us, for the overwhelming desire of society today is to assume that equal capacities and abilities are a universal heritage of humanity. It may well be. But simply wanting this to be the case is not enough. That is not science. Our DNA tells contrasting stories: the early, crude map suggested that we are individuals with a shared past, while a magnified look at our genes finds patterns of small but meaningful population differences. The challenge is to harmonize these competing narratives of unity and separation. The great paradox of human biodiversity research is that the only way to understand how similar humans are is to learn how we differ. The thorny reality is that if all of us were alike, the entire Human Genome Project would be fruitless. That's the constructive dialogue I am hoping that Abraham's Children will encourage.