"Sexual dimorphism has been talked about for years," he says. "I fear that what they're basing this on is not an erectus, and the base of the house of cards will collapse. Let's go slowly and not assume erectus or habilis and think about what else it might be."
Whatever the results may be, Manthi, from the National Museums of Kenya, still rates his 33rd birthday as one of the best he's had.
"I've worked in the lake basin for 20 years," the Kenyan native, now 40, says. "This was my first human fossil."
Robin T. Reid is a freelance writer and editor in Baltimore, Maryland.