By >Daniel Zadik , Leicester University 

The DNA of Albert Perry may change the story of human origins. Perry, an African-American, approached a DNA testing company to find out more about his ancestry. >The results would have come as quite a surprise (had he lived to see them), and have raised questions >for geneticists around the world. 

It turns out that Perry carried a very different type of Y chromosome, never seen before. Every male has a Y chromosome, which is a piece of DNA inherited by sons from their fathers. But, unlike most DNA, the Y chromosome is not shuffled as it is passed down, and changes only slowly through mutation. Tracking these mutations allows scientists to create a genetic tree of fathers and sons going back through time.

As a man may have several sons or none, some branches of the genetic tree die out each generation, while others become more common. Going back through time it is therefore inevitable that all modern Y chromosomes must descend from from one man at some point in the past. He has become known as “Y-chromosomal Adam”.

This Adam was not the first man, or the only man, from his time to contribute to modern human DNA. It is just that, by chance, his Y chromosome was the only one to survive until today.

What is surprising about Perry’s Y chromosome is that it did not descend from Y-chromosomal Adam’s. Or rather that the established “Adam” has lost his title to a new “Adam”, further back in time, where Perry’s branch split from the tree (see figure). While the former-Adam is estimated to have lived around 202,000 years ago, the revised one is thought to be about 338,000 years old.

To find where Perry’s Y chromosome may have come from, samples from around Africa were tested. Several more from Perry’s branch were found amongst the Mbo people of Cameroon.

So can this tell us anything about human origins? Central Africa contains Y chromosomes from both Perry’s branch and the former-Adam’s branch, while the rest of the world has only been shown to contain the former-Adam’s branch (with the exception of Perry himself). This suggests that our revised Adam may have lived in Central Africa.

The oldest-known “modern human” bones are from East Africa. But if Adam lived in Central Africa, does that mean that modern humans could have originated there? Again, it is hard to say. By looking further into the >genetics of modern people , the picture becomes even more complex. 

It so happens that, just like the Y-chromosome is passed down only from father to son, there is a piece of DNA which sits in a different part of the cell called mitochondria, that is passed down only from mother to her children. Tracing back this DNA in a similar way, leads us to a “ >Mitochondrial Eve ”, estimated to have lived about 190,000 years ago. Eve possibly lived in south-eastern Africa. But modern humans have DNA both from Adam and Eve. 

Despite these apparent contradictions, it is possible that modern humans descended from a single localised population, and that geographical differences in diversity today are due to spread and extinction in the intervening years. But it could also be that many of >the genetic and cultural ingredients that produced modern humans existed in different parts of Africa, drifting and spreading until they came together and, by a mixture of luck and natural selection, became the combination that would out-compete their relatives to spread to the rest of the world. 

One way or another, around 200,000 years ago, bones appear that are indistinguishable from today’s. But that is 140,000 years later than the estimated age of the new Adam, leading to the question: was he even “human”?

Answering this is tricky. There was no single moment when we became human, but rather a >gradual process . On an evolutionary timescale, Adam was very recent, and even if he was not “anatomically modern”, he could probably walk down a street today without raising too many eyebrows. 

Given the scarcity of Perry’s branch and the lack of diversity within it, it is also possible that the revised Adam could have been an ancestor of two sub-species (or even species). Could one have become modern humans, while another produced a cousin? What if, long after modern humans had become established and started to spread, they should meet and interbreed? Like all our other close relatives, these cousins eventually disappeared, but maybe they left traces, such as Perry’s Y chromosome, in the modern gene pool.

This may sound shocking, but it would not be unprecedented. When modern humans spread from Africa to Eurasia, they met another cousin, the Neanderthals. Fossils with features from both species have long caused debate, and recently genetic evidence has suggested that today’s non-Africans owe 1 to 4% of their ancestry to >such interbreeding , although no Y chromosomes have yet been identified. 

So, like many discoveries, Perry’s Y chromosome raises more questions than it answers. It will doubtless be fascinating to watch our understanding evolve as the genetics of more individuals, modern and ancient, from more locations are added to the picture.

Daniel Zadik does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations. 

This article was originally published at >The Conversation . Read the >original article . 

Published – July 22, 2013 06:37 pm IST

A fossilised skeleton, Australopithecus afarensis, best known by her nickname ‘Lucy’, was unearthed by researchers 50 years ago this month in the Afar region of Ethiopia. It eventually went on to transform scientists’ understanding of human evolution.

Opening a new chapter in human history, the discovery by Don Johanson, an American palaeontologist and graduate student Tom Gray on November 24, 1974, provided proof that the ancient hominins could walk upright on two feet 3.2 million years ago — a trait thought to have evolved more recently, CNN reported.

Lucy had a mixture of ape and humanlike traits, suggesting she occupied a pivotal branch in the family tree of humans. Over the past few decades, she has encouraged multiple researches and debates, besides igniting a broader public fascination with human origins.

Although researchers have now unearthed fossil hominins twice as old as Lucy, she continues to remain a key subject for scientific studies.

At the time when it was found, Lucy had 47 bones and was the oldest known and the most complete skeleton of early human ancestors.

Reminiscing his 1974 Ethiopia visit, Don Johanson told CNN he was walking on sediment 3.2 million years in age to search for the fossilised remains of various kinds of animals, “but particularly the remains of our ancestors.” 

“I happened to look over my right shoulder. If I had looked over my left shoulder, I would have missed it,” he said.

At first, he witnessed a little fragment of bone, a little part of the elbow as well as a part of a forearm. 

He could tell “immediately that it was from a human ancestor,” Johanson said, adding when he and his student, Tom Gray, kneeled to have a closer look, they saw “fragments of the skull and fragments of a pelvis and fragments of an arm bone and the leg bone.” 

“I realized at that moment that here was the childhood dream… I’d always wanted to go to Africa to find something and by golly this was something. But we didn’t know how much it would become an icon in the study of human origins,” Johanson said.

At the time of discovery, Lucy’s bones were “very fragile” because they had mineralised and changed into stone. So, the team did a “very careful crawl to pick up the obvious pieces,” before they put them into the burlap bags.

Later, they water-washed them in the stream via fine screening. The whole process took two and a half weeks. 

Johanson recalled it was wonderful to see Lucy come together on the lab table in the field. “The femur there was only about a foot long, or 28 centimetres long. What is this? I thought. Is this a child? Well, let’s look at the jaw. The wisdom teeth had erupted so she was an adult. But my god, if this was an adult, it had to have been only about 3 and a half feet tall, a meter tall,” he added.

Asked how it got the name Lucy, Johanson said it had a delicate nature of the bones and the short stature, so they felt “she was probably a female.”

He went on to say that while Lucy’s species did not give rise directly to modern humans, “her pivotal place on the human family tree led to all later hominin species, most of which went extinct.” 

“The Homo lineage persisted and ultimately gave rise to us, Homo sapiens,” he concluded.

 

An undated artist’s impression of members of the extinct archaic human species called the Denisovans seen in the landscape of Ganjia Basin on the northeastern edge of the Tibetan Plateau in China’s Gansu province, depicting some of the animals whose bones were found at Baishiya Karst Cave.
| Photo Credit: Reuters

Thousands of bone fragments discovered in a cave on the Tibetan Plateau in China are offering rare insight into the lives of Denisovans, the mysterious extinct cousins of Neanderthals and our own species, showing they hunted a wide range of animals from sheep to woolly rhinoceros in this high-altitude abode.

Researchers studied more than 2,500 bones found inside Baishiya Karst Cave, which is situated 10,760 feet (3,280 meters) above sea level and previously had yielded Denisovan fossil remains.

They used ancient protein analysis on these remains to reveal that the Denisovans exploited various animals for their meat and skins, and also excavated and identified a rib bone from a Denisovan individual dating to 48,000-32,000 years ago – the youngest Denisovan fossil yet known.

Most of the bones were identified as belonging to blue sheep, also called bharal, a goat species still seen on high slope mountains and cliffs in the Himalayas. Other bone remains came from woolly rhinos, yaks, small mammals like marmots, birds, and even from the spotted hyena, a large carnivore that prowled the region called the Ganjia Basin.

It was a grass landscape with small forested areas, teeming with life despite harsh conditions. The animals were butchered for meat, based on cut marks found on various bones, and there was evidence of bone marrow extraction and skinning activities. The researchers also found four tools fashioned from animal bone, shaped for use in processing animal carcasses.

“It is the first time we have gotten an understanding of the subsistence behaviors of Denisovans, and it shows us they were highly capable of accessing and utilizing a wide range of animal resources,” said University of Copenhagen molecular anthropologist Frido Welker, one of the leaders of the research published on Wednesday in the journal Nature.

“I think the diverse animal remains found in Baishiya Karst Cave suggest that this location offered relatively better resources compared with the neighboring higher Tibetan Plateau to the west and the Chinese Loess Plateau to the north, especially in the glacial period,” said archeologist Dongju Zhang of Lanzhou University in China, another of the study leaders.

The existence of Denisovans was unknown until researchers in 2010 announced the discovery of their remains in Denisova Cave in Siberia, with genetic evidence showing them to be a sister group to Neanderthals, the stoutly built extinct archaic humans who inhabited parts of Eurasia. Both experienced significant interactions with Homo sapiens, including interbreeding, before vanishing soon after for reasons not fully understood.

“From genetics, we know they diverged from Neanderthals around 400,000 years ago,” Welker said.

Denisovans are known only from dental remains and bone fragments from the Baishiya Karst and Denisova caves and Cobra Cave in Laos, though their existence at those three far-flung locations demonstrates a wide geographic dispersal.

Their presence at a high latitude in Siberia, a high altitude on the Tibetan Plateau and a subtropical location in Laos “implies that Denisovans had high flexibility to adapt to different environments,” Zhang said.

A lower jaw of a Denisovan adolescent previously found at Baishiya Karst is 160,000 years old. The researchers suspect Denisovans were present there as far back as 200,000 years ago. The newly identified rib fragment shows that Denisovans still existed as recently as 48,000-32,000 years ago.

“We don’t know if the rib was from an adult or a child, nor its genetic sex. It is the first time a rib specimen has been identified as a Denisovan. Previous remains are all dental or cranial or mandibular (lower jaw),” Welker said.

Our species, Homo sapiens, did not populate the Tibetan Plateau until about 40,000 years ago, having first appeared in Africa a bit more than 300,000 years ago.

So what happened to the Denisovans?

“Great question. We know so little,” Welker said. “We know that Denisovans interbred with modern humans. We know that based on some Denisovan DNA that is present in the genomes of some modern humans living today. But when, where and why Denisovans ultimately went extinct, that we don’t know anything about.”

A novel genomic analysis technique has helped reveal the reasons for a ‘bottleneck’ in the growth of the human population that almost wiped out the chance for humankind as it exists today.
| Photo Credit: AFP

A novel genomic analysis technique has helped reveal the reasons for a ‘bottleneck’ in the growth of the human population that almost wiped out the chance for humankind as it exists today, scientists reported in a study published in Science.

The findings indicate that the early population of human ancestors went through a period in which approximately 1,280 breeding individuals were able to sustain a population for about 117,000 years, the researchers from China, Italy, and the U.S. said.

They were able to determine demographic characteristics using modern-day human genome sequences from 3,154 individuals and a new analytical method called fast infinitesimal time coalescent process (FitCoal).

FitCoal helped the researchers calculate a probable population size through history based on contemporary sequences. They reported as a result that early human ancestors experienced extreme loss of life and, therefore, loss of genetic diversity.

Giorgio Manzi, an anthropologist at Sapienza University of Rome and a coauthor of the paper, said that the gap in “the African and Eurasian fossil records” can be explained by this “bottleneck in the Early Stone Age”.

The reasons suggested for this downturn in the size of the human ancestral population include glaciation events, leading to changes in temperature and severe droughts, and the loss of other species, potentially those that were food sources for ancestral humans.

An estimated 65.85% of humans’ current genetic diversity may have been lost in this period, in the early to middle Pleistocene era (from two million to 11,000 years ago), and the prolonged period of a minimal number of breeding individuals could have threatened humankind as we know it today, the researchers said in their study.

However, the bottleneck also seemingly contributed to a speciation event in which two ancestral chromosomes may have converged to form chromosome 2 in modern humans, the researchers said.

“The novel finding opens a new field in human evolution because it evokes many questions, such as the places where these individuals lived, how they overcame the catastrophic [climatic] changes, and whether natural selection during the bottleneck accelerated the evolution of the human brain,” said senior author Yi-Hsuan Pan, a researcher of evolutionary and functional genomics at East China Normal University, China.

Now that there is reason to believe that humans grappled with a struggle 930,000-813,000 years ago, researchers can continue digging to reveal how such a small population persisted in presumably dangerous conditions, the study said.

Humankind’s rebound is expected to have been due to the use of fire and the arrival of more favourable climates.