Others, such as Bishop Adam J. Richardson Jr. of the Washington area district of the African Methodist Episcopal Church, said that it's hard to quantify matters of the spirit and that attributing behavior to one's genetic makeup "can be a frightful thing." By analogy, saying that people are predisposed to be spiritual also means that criminals are genetically wired to be criminals and have no hope of rehabilitation.
"Why not just put them in prison and throw away the key?" he asked.
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Richardson said there's also the danger of people losing hope, of believing their genetic makeup limits their development and personal growth. "In my own system, we do have choice. We always have choice," the bishop said.
Hamer said his own religious development began in a Congregationalist church, which he abandoned when he became a scientist. But he discovered new spiritual meaning when he began researching this book -- through, in part, Zen meditative practices he learned at a Zen center near Kyoto, Japan.
He likens spirituality to the capacity for language: Humans are genetically predisposed to have it, but the language people speak and the religion they practice are learned rather than inherited characteristics.
People are designed to communicate through language, but they speak English, French or Chinese because of the part of the world they grew up in. Similarly, genetic makeup urges people to believe in a Creator or find spiritual fulfillment, but culture, history and environment determine whether one is a Christian, Hindu, Jew, Buddhist or Muslim.
Although people can change or abandon that religious affiliation, they cannot rid themselves of the genetic propensity to be spiritual. But people can build on and develop that innate spirituality through meditation, prayer and creative arts such as music and painting. These practices can be done inside or outside organized religion, he said.
Hamer said he has received numerous comments from people who say that the dichotomy of spirituality and religion makes sense. "I always knew this, that I was inclined to be spiritual, even though I've always had a problem with religion," they tell him.
"I see more and more people doing things like yoga," Hamer said. "They do it initially because they want to get more flexible and look good and feel great. Then they find that once they spend some time sitting on a mat, doing nothing but concentrating on their body and clearing their mind of everything else, they say, 'That feels kind of good.' "
Such feelings can lead to an intuitive sense of God's presence, Hamer said. "We do not know God; we feel Him."
Organized religion can become so codified, so caught up with learned rituals, that the focus on spirituality gets lost, Hamer said. The resurgence of Pentecostalism and other emotion-based religions is one sign of the staying power of inherited spirituality, he said.
Megachurches, too, are part of this phenomenon and have widespread appeal because of the emotional aspects of worship, he said. "They have lots of music, video screens, the whole multimedia thing going on," he said. "They're tapping into that [innate spirituality]. It's fun and allows people to get into that spiritual frame of mind."
Hamer said more research has to be done to determine whether there is a genetic basis for other religion-related phenomena, including the existence of archetypes, the similarity of creation stories in various religions and the common characteristics of fundamentalism in Christianity, Judaism and Islam.
Also left hanging is why women score much higher than men on transcendence tests.
"I'm not completely sure about that," Hamer said. "I just know that it's true. Women are more attuned to their emotional connections, and that's at the heart of spirituality."