Sunday, November 1, 2009
The Missing Link by Colin Tudge
At its core, the story of human evolution is itself an evolving narrative, leading- in fits, starts and many blind alleys- from how we came into existence to who we are today. The details that we do have reveal that all humans are interconnected and related at some root level. But the story is a frustrating work in progress, told in long chapters filled with many blank pages.
Much of the evidence comes from fossils, at best an imperfect means of speaking to us. From a fossil to form, the creature must die in specific conditions. It must be covered soon after death in order to prevent it from being eaten by other creatures or decomposing due to the presence of bacteria. The creature's resting place must remain geologically stable for millions of years. And then it has to be found, properly extracted, and compared to the rest of the record. Only at that point can a new piece be added to the puzzle of our past and, possibly, contribute to what we understand about ourselves.
Sometime in 1982, on a routine day for most of the world, a man living on the outskirts of Frankfurt went on a day expedition to the coal- shale quarry in Messel, hoping to ad to his private fossil collection. While splitting the layers of shale, the fossil hunter stumbled upon a specimen which looked like an exotic monkey crushed to the thickness of a silver dollar- frozen in a fetal position, exactly as she had come to rest on the bottom of the ancient lake whose geological development formed the substance and structure of the pit in Messel.
The man realized he was on to something. He carefully extracted the fossil from the ground and diligently wrapped it in wet newspaper. He then returned to his house and probably employed an expert to prepare the fossil- its preparation was so skillful that just a handful of people in the world could have done it. It must have taken months of careful chipping away the shale and stabilizing the bones before the specimen was ready to be placed on a shelf in his basement with the others that he had excavated, away from the eyes of science and the public, for him alone to see.
In 2006 the anonymous man who discovered the fossil which has since been dubbed 'Ida" put it up for sale at the Hamburg fossil fair (the second largest such fair in the world) where it came to he attention Jorn Hurum, associate professor of paleontology at the Natural History Museum at the University of Oslo, which finally agreed to purchase "Ida" for one million dollars.
Jorn Hurum and his team of scientists concluded from their first comprehensive study of Ida -the most complete fossil primate ever found- that she will have a significant place in the story of human evolution. At her simplest, Ida was a small leaping primate, probably nocturnal and probably vegetarian who lived 47 million years ago in a tropical forest not unlike the ones found in South America today. She died after encountering toxic gas released from the ancient crater lake, a recently broken right wrist and weak left arm had probably brought her to the ground by the shore and prevented her from scurrying to safety. Her remains were fossilized along with the gut contents of her last meal intact.
Remarkably, Ida displays characteristics of wet-nosed and dry-nosed primates, the prosimians and the anthropoids. However, she is a sui generis species. Her eyes are completely stereoscopic. She has a fused cranial plate, indicating increased brain growth. Her lower mandible is fused and her teeth are spatulate. Most important for placing her in the primate evolutionary chain, she doesn't possess a toothcomb or grooming claw, which are innate lemur traits.
Hurum and his team have concluded that Ida documents the moment when early primates were just about to split into two different lineages. Each lineage was successful in its own right, but at the end of the anthropoid lineage is the human, the most successful primate to have walked the earth. In other words, Ida appears to be an in-between species, or one of the long-sought missing links in evolution.; the biggest breakthrough in our understanding of primate evolution in thirty years.