A visiting biology professor showed that the majority of threatened species have low genetic diversity, bolstering the scientific view that genetic factors are a threat to species heading toward extinction.

Richard Frankham, who served as Hrdy visiting professor in the Department of Organismic and Evolutionary Biology last spring, said the work completed during his stay at Harvard has potential major implications for how threatened and endangered species are managed.

An ongoing debate among biologists concerns whether the inbreeding that results when a population is reduced to a small number of individuals is immediately harmful or whether species are driven to extinction so fast by other factors that genetic issues don’t really have an effect.

Frankham, who has returned to his post as a visiting professor at Macquarie University in Sydney, Australia, and colleagues reviewed the genetic diversity of 170 threatened species and found that 77 percent of the species had lower genetic diversity than that found in the closest-related nonthreatened species.

Most surprising, Frankham said, was the level of the decline, with an average of 35 percent less diversity in threatened species compared with nonthreatened ones.

This connection, Frankham said, shows that genetic factors do exist in threatened species and have the potential to impact species survival. That is important to understand, he said, as conservation plans are crafted for the species’ recovery. He gave the example of recovery efforts for the Illinois population of the greater prairie chicken, for which recovery efforts failed until the population was outcrossed with individuals from another population to reverse genetic problems.

“If genetic factors are ignored, then the probability of extinction is likely to be underestimated, and recovery programs may not work or be suboptimal,” Frankham said.

The research appeared in a recent issue of the Proceedings of the National Academy of Sciences.

Frankham taught ESPP 90e, “Conservation Genetics,” while at Harvard, wrote several scientific papers, gave several seminars, and delivered the Dick Taylor Memorial Lecture.