Reading practice 42
Underground.
The "big secret" and "missing link" are one and the same: a 47-million-year-old, uncannily preserved fossil of an ancient ancestor of the primate family, nicknamed Ida. After two years of secretly performing research on the fossil, experts are ready to present their findings to the world1. They firmly believe that the lemur monkey they have preserved in polyester resin is conclusive evidence of a transitional species, a fork in the road where the genetic tree branches off in the direction that eventually gives rise to such simian species as monkeys, apes, and humans.
Two things make this particular specimen so valuable. It is older than any previously found primate fossil, vastly predating the previous record-holder, Lucy, which is a 3.18-million-year- old fossil2. Furthermore, it is one of the most complete fossils ever found, with 95% of the skeleton preserved. In fact, the fos- silization conditions were so perfect in Ida's case that scientists could actually still analyze the last meal Ida had before apparently falling into a crater and dying of carbon dioxide poisoning. By contrast, Lucy's remains were only 40% complete, lacking a skull among other important features.
For the next two years, a team of top scientists studied Ida's features and attempted to integrate the information into the genetic tree of the primates. All the while, the scientists knew they were on the cusp of providing the most conclusive evidence yet of the accuracy of Darwin's theory of evolution3. However, they had all signed non-disclosure agreements that prevented them from discussing these tentative findings with others in the field or the media.
Charles Darwin's revolutionary book The Origin of Species, published in 1859, first detailed the theory of natural selection. It was extremely controversial in its time, and its contention that humans evolved from a lineage of monkeys remains an uncomfortable idea to many even to this day. Despite the 98.4% genetic similarity that humans have to chimpanzees4, many of Darwin's skeptics have routinely rested their cases on the fact that there was a gigantic hole in the fossil evidence that relates to where the branch of higher primates begins.
Around 50 million years ago, the first primates are thought to have emerged, two different species called tarsidae and adapidae. Scientists have been unsure which species ultimately led to the higher primates (monkeys and humans). The discovery of Ida, an adapid with several human-like features, suggests that adapidae are the ancestors of modern humans5.
With so many anatomical features vividly preserved in Ida's fossilized remains, scientists have been able to identify several telltale similarities Ida has to modern humans. One feature that distinguishes Ida's species from non-anthropoid primates is the talus bone, a bone that turns the corner between the leg and the foot. Her eyes face forward, which makes her visual fields overlap, a requirement for accurate depth perception. Her hands and feet have nails, rather than claws6, and opposable thumbs. Both characteristics allow for the use of appendages in a more refined way, whether it be peeling fruit, climbing, or, in the case of humans and their closer ancestors, using tools.
The debate over evolution is likely to continue for many years. However, the discovery of Ida has given evolutionary scientists a stronger supporting piece of evidence than they ever dreamed was possible. As Harold Zemeckels, a professor of evolutionary biology at Emerson University, puts it, "This fossil is essentially a prayer answered, a perfect time capsule that's been miraculously gift-wrapped for posterity."
