This Tacoma professor spent years in Africa rewriting what we know about evolution

When did our ancestors go from walking on all fours to just two? It’s a question that researchers have been trying to answer for a century. Last week, a Tacoma Community College anthropology professor and 36 other researchers published findings in the journal “Science” that push clues to that major development back by 11 million years.

It all has to do with grass in ancient Africa.

TCC professor Kirsten Jenkins is a paleoanthropologist. She studies human and ape evolution through the fossil record.

“Whenever you find a fossil, you could be the first person who’s seen that, held it, touched it in 20 million years,” she said.

For this decade-long project conducted in Kenya and Uganda, Jenkins served as the research team’s taphonomist. She studied how certain fossils became preserved and ended up where they did — a crime scene investigator for events that happened million of years in the past.

“Sometimes, the way things die together can tell you clues about how they lived together,” she said. “Do they have marks and scratches on them that are indicative of, say, a predator? Or did they just float in a river?”

By understanding past habitats, researchers can gain insight to the evolutionary pressures ancient apes faced. That was the impetus for the peer-reviewed study.

The surprising conclusion from the team of 37 specialists with a wide range of expertise was that grasslands developed in eastern African 11 million years earlier than previously thought. Those grasslands played an important part in the road to human evolution.

“None of us expected this,” Jenkins said. “We just didn’t have to convince ourselves, we had to convince each other.”

Grasslands

Previously, grasslands were thought to have developed 10 million years ago. Jenkins and her team pushed that date to 21 million years ago in the Miocene epoch.

The finding is significant because ancient apes in those areas would not be able to swing from tree to tree for foraging. They would have needed to move more frequently on the ground, unlike today’s apes which live in dense forests.

When studying the prehistorical habitats of ape ancestors (which include humans), it helps to know if they were living in dense, tropical forests like gorillas do today or in lightly forested woodlands with a lot of grass and more seasonal growing patterns.

A variety of ancient apes roamed Africa at that time, including Morotopithecus in what is present day Uganda.

The challenge came in finding plant fossils alongside ape fossils. Grasses don’t fossilize like bones do, Jenkins said. Instead, the team used ancient soil geochemistry and phytoliths, microscopic particles made of silica that are found in plants and persist long after the plant has decayed.

On the road to bipeds

The grasslands finding can explain why ape fossils from the Miocene show a transition from a monkey-like body shape to a gorilla-like, or human-like body with a wider torso. The researchers aren’t saying these ancient apes were bipedal but the findings provide another piece of the puzzle in understanding the switch from walking on all fours to bipedalism.

“Their torsos are wide,” Jenkins said. “Their torsos are upright. But they’re not necessarily doing bipedalism. And you contrast that with monkeys, (which) have a torso that’s much more like a cat or a dog, or even a cow.”

Until this research was conducted, it was thought that Miocene apes were all living in dense forests and living on a largely fruit diet.

“But what we’re seeing is that’s not necessarily the case,” Jenkins said. While many Miocene epoch apes did live in dense forests, others lived in grasslands and ate leaves.

“Some of them developed this new body plan (before bipedalism),” she said. “They actually have teeth that look like they would eat leaves rather than fruits.”

The researchers hypothesize that the body plan evolved initially to aid in climbing and descending trees for leaf foraging.

The sites

Jenkins and her fellow researchers are from all over the world, including Kenya and Uganda. Sometimes, they found fossils lying on the bare earth waiting to be found. At other sites, digging was required.

“Some of these fossil sites will have nice beautiful ape fossils,” Jenkins said. “Some of them will have fossils with all these other animals, too. I’ve worked on digs that are chock full of crocodiles and rhinos and these weird carnivores.”

Living out of a tent, away from family for weeks at a time, can be challenging, she said.

“Some of the these environments are intense,” she said. “Some of them are really hot. Some are cold.”

Are these human ancestors?

Gorillas and humans diverged 10 million years ago. Humans and chimps diverged six to seven million years ago.

Today, only humans are truly bipedal. The evolutionary move helped make Homo sapiens the dominant primate on earth. Freeing up hands allowed our ancestors to carry children, tools, weapons and other items. It also allowed them to see over tall grasses.

But Jenkins doesn’t assign a high value to grasslands as being a prime driver in bipedalism. She’s more in the “it’s handy to have hands” camp.

“It kind of gives me pause about thinking about the savanna hypothesis for the development of bipedalism,” Jenkins said. “I think environment had to play some role, but that’s probably not the only role.”

‘Missing link’

Just in the past decade, stone tools have been found with human ancestory Australopithecus fossils, Jenkins said. It only took about 4 million years for our ancestors to go from carrying rocks to carrying iPhones. Until Jenkins’ study, it was thought that grasslands developed just prior to the rise of Australopithecus afarensis — the famous “Lucy” fossil.

The so-called “missing link” in human evolution is a misnomer. The lineage of human evolution is more like a vast family tree with clearly recognizable forebears, dead ends and blank spaces.

While some species, like the bipedal Australopithecus are clearly in our lineage, it can’t yet be determined if Morotopithecus is an ancestor.

“We don’t actually know who is a descendant of whom, just yet, in the early Miocene” Jenkins said. “And that’s something that we’re definitely interested in finding out.”

The big picture

Her own research has changed the way Jenkins thinks about ape evolution. Before, she would have been a naysayer to the idea that East Africa had grasslands 21 million years ago.

“I think it really changes the view of the early Miocene,” she said of her team’s work. “There’s increasing recognition that if we really want to understand our own human evolution, we have to understand broader ape evolution as well.”