BU Professor Digs Up Clues To Human Origins

How did homo sapiens develop into the creatures we are today?

Philosophers and theologians have explored this question in the past but more recently biological anthropologists, like Boston University professor Laura MacLatchy, have taken up the investigation. MacLatchy's research into human origins has added pivotal information to our knowledge of how humans evolved.

MacLatchy's paleontological fieldwork has taken her to Chad, Egypt, Kenya, Malawi, Pakistan and Uganda. For six years, she directed a project in eastern Uganda that uncovered fossil evidence of a newly discovered species called Morotopithecus Bishopi, dating to 21 million years ago. This species may offer insight into adaptations that led to differences between modern day apes.

"This research puts modern humans in a context," she said. "It is useful to understand how long we have had morphological, and behavioral adaptations.

"We can use the fossil and archeological record to tell us how long we have been what we are," she added. "For example, human dimorphism [size and structural differences between the sexes] is moderate; this correlates to our social organization being mildly polygynous."

Most primate fossils that date to more than 20 million years ago show adaptations for movement on four legs, called quadrupedalism. The Morotopithecus discovery, however, shows a completely different locomotor pattern: suspensory locomotion, like swinging from branch to branch in trees.

This suspensory pattern is believed to fill an important transitional role in the development of primates. Many anthropologists believe primates evolved from quadrapedal ancestors into suspensory primates and finally into the bipedal creatures we see today in humans.

Morotopithecus shows a mixture of both primitive and modern features. It had a face and teeth resembling earlier species, while the lower spine, legs, and shoulders show a new design allowing suspension from branches. Being able to support an upright posture more easily than previous species meant Morotopithecus could more easily take advantage of the food and shelter found in trees.

Before the discovery of Morotopithecus, the oldest evidence of species with locomotion and body form like that of any living species was 10 million years old. Morotopithecus pushes that threshold back to at least 20 million years ago.

Although Morotopithecus was not a hominoid (a close human ancestor), the find does give us some information about human evolution.

"They tell us mostly about the origins of apes. Obviously, a lot of the adaptations seen in these and the living apes are precursors for bipedality," MacLatchy says. "For example, before humans could walk upright, the apes needed to develop a stable lower back."

Because Morotopithecus' suspensory adaptations are a precursor to bipedality, experts are debating about why primates later evolved to walk upright. Scientists debate over how exactly the process occurred, when it happened, and what advantage the shift would have offered to allow natural selection to favor an upright stance. There are many ideas of what caused bipedality. Among them are holding tools, carrying food, picking fruit, running when threatened by predators or staying cool since a two-legged stance exposes less body surface to the sun than a four-legged one.

Still other researchers think bipedality evolved so these primates could look tougher. Many apes rise to two feet during displays of aggression, and by adapting to make this position more comfortable for longer periods of time, apes might have gained a reproductive or defensive advantage.

Humans, as well as chimpanzees, orangutans, gorillas and gibbons, are part of a group known as the hominoids. Scientists estimate that these modern apes split from the primitive apes and the Old World monkeys 20-25 million years ago. Because Morotopithecus shares features of both modern and primitive apes and dates to 21 million years ago, researchers are encouraged that their estimation is correct. In other words, Morotopithecus is the oldest known close relative of the living apes, and the oldest primate that shows such clear-cut resemblance to modern species.

MacLatchy separates her scientific research from social prescription.

"A trait does not necessarily have a positive value simply for having a biological cause," she says. "Most people today recognize that there is both a huge biological and a cultural component to human behavior. If we understand that our behavior has a biological component, we can better understand or even modify it. Far from justifying a behavior on the grounds that it is biological, and therefore somehow 'natural', we can perhaps be given better means to change."

Other recent developments in biological anthropology and human origins, a field MacLatchy describes as "dynamic, having a lot of resonance for a lot of people," also have come out of Africa. From Ethiopia, fossils of a species called Ardipithecus date from 5 – 5.5 million years ago. This is quite close to the species that is believed to have linked humans and chimpanzees between 6 – 7.5 million years ago.

MacLatchy, in addition to teaching courses in primate and human evolution and anatomy, is advisor for the Anthropology in the Works program, a social and academic group that acts as a forum for undergraduate and graduate students interested in anthropology. She also is a member of both the Center for Ecology and Conservation Biology, and the Society of Vertebrate Paleontology.

Boston University has only recently begun to emphasize biological anthology to augment its already strong sociocultural anthropology program. The biological anthropology program began in the fall of 1998. The first biological anthropologist on faculty was neuroscientist Terrence Deacon in 1992, followed by MacLatchy and Benjamin Campbell in 1998. Boston University provided some funding for Dr. MacLatchy's work in Uganda this summer. The L.S.B. Leakey Foundation, a group especially interested in understanding human origins, provides much of her funding.

No Morotopithecus material was found when MacLatchy returned to Uganda this past summer. However, she did find fossils attributed to a smaller ancient ape, one the size of a gibbon. Other discoveries from the site yielded information about another group of primates known as lorises. A femur found at the site and dated to 20 million years of age shows that by that time, the "loris" subgroup had already begun to adapt to slow climbing. According to MacLatchy, such information is "just another piece in the puzzle."