November 1, 2013 6:36 pm

Science: support for single ‘Homo’ theory

Study suggests that differences seen between hominid fossils of humans living 1.8 million years ago represent normal variations within one species
The five skulls found at Dmanisi, Georgia©M Ponce De Leon and Ch. Zollikofer, Zurich

The five skulls found at Dmanisi, Georgia

Scientists who study our human origins tend to follow two alternative storylines. One emphasises complexity, with lots of hominid species evolving and dying out until Homo sapiens was left alone and triumphant 20,000 to 30,000 years ago. The other account concentrates on the central trunk of human evolution, dismissing side branches as speculation based on fragmentary fossil evidence.

This second view is boosted by a paper in Science which analyses five skulls of early humans who lived 1.8 million years ago in what is now Dmanisi, Georgia, and compares them with fossils of a similar age from elsewhere in Asia and Africa.

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The researchers from the Georgian National Museum and Zurich Anthropological Institute and Museum conclude that all these remains come from the same species, Homo erectus, as it evolved over time. The analysis suggests that the differences seen between hominid fossils of this period represent normal variations within one species and that there is no need to invoke others such as Homo habilis, Homo ergaster and so on. “The amount of variation does not exceed that found in modern populations of our own species, nor in chimps or bonobos,” says Christoph Zollikofer of the Zurich institute.

Excavations at Dmanisi have yielded the oldest and finest human remains outside Africa. They date from a key period in human evolution when earlier hominids such as Australopithecus, to whom the old-fashioned term apeman might reasonably apply, had evolved into the genus Homo. At the same time, humans began to sweep out of Africa and moved across Asia.

©Art courtesy of J.H. Matternes

A graphic representation based on the largest skull

The intact skulls uncovered so far at Dmanisi belong to three men (one elderly and toothless), a young woman and an adolescent of unknown gender. The most recent, known as skull five, is male with the largest face and jaw of the group but the smallest brain case – just a third that of a typical modern man.

Zollikofer says the finds “look quite different from one another so it’s tempting to publish them as different species. Yet we know that these individuals came from the same location and the same geological time, so they could… represent a single population of a single species.”

Fossils of the early Homo period show similar variation across Africa but, unlike Dmanisi, most are single fragmentary finds without other fossils from the same time and place to put them in a group context. Their discoverers also tend to assume that they have found bones typical of the species, ignoring variation within species. As Marcia Ponce de León of Zurich puts it, “At present there are as many subdivisions between species as there are researchers examining this problem.”

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Hodgkin gene link to MS

A fascinating genetic link is emerging between two diseases associated with the immune system: multiple sclerosis and Hodgkin lymphoma.

Scientists at the Institute of Cancer Research in London compared the DNA of 3,500 people with Hodgkin lymphoma, a cancer of the lymph nodes, and 8,300 people without the disease. They found two new genetic variants that increase the risk of lymphoma; both are involved in the development of the immune system.

The study, published in Nature Communications, increases the number of genetic variants known to be risk factors for Hodgkin lymphoma from three to five. One of the newly discovered mutations is particularly interesting because it is linked to a gene known as EOMES, which also increases the risk of developing MS. This might explain why cases of Hodgkin lymphoma and MS cluster together in families.

Every year 2,500 to 3,000 people in the UK are diagnosed with MS, an autoimmune disease affecting the brain and spinal cord. The number of new cases of Hodgkin lymphoma is slightly lower, at about 1,900 a year; about half of these occur in people who have previously contracted Epstein-Barr virus, the infection that causes glandular fever.

“Although many people are aware of the link between Hodgkin lymphoma and the glandular fever virus, we are also uncovering more and more evidence of the genetic nature of the disease,” says Richard Houlston, professor of molecular and population genetics at The Institute of Cancer Research.

All ears

The tiny Gardiner’s frog from the Seychelles has no middle ear or eardrum yet responds to sound. An X-ray study showed that it uses its mouth to amplify and carry sound to an inner ear.

“Our immune systems must strike a fine balance between, on the one hand, remaining vigilant to infections or abnormalities such as cancer and, on the other, not becoming overactive and attacking the body’s own tissues,” says Alan Ashworth, ICR chief executive. “Scientists are only just beginning to understand the implications for our risk of cancer of disruptions to this balance.”

A shared immune mechanism between MS and Hodgkin lymphoma might be exploited through new treatments for both diseases, Ashworth adds.

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Sugar plays key role in plants’ internal clock

Chlorophyll

Chlorophyll fluorescing in thale cress seedlings

Plants, like animals, have a 24-hour clock that controls their circadian rhythm so that, for example, their biology is primed to take advantage of sunrise. Now a study from Cambridge university shows that sugars are the key to its timekeeping.

Earlier research had shown that plants’ internal clocks consist of a network of feedback loops between genes that switch each other on and off. But scientists were not sure which external cues ensured that the clock was properly synchronised with the plant’s environment.

The Cambridge study, published in Nature, used Arabidopsis or thale cress to investigate the effect on its internal clock of altering the amount of sugar produced by photosynthesis. When the scientists prevented photosynthesis by genetic manipulation or by growing Arabidopsis in air free of carbon dioxide, the plant’s timekeeping slipped, even though the cycle of light and dark and other potential cues were not changed.

“Our research shows that sugar levels within a plant play a vital role in synchronising circadian rhythms with its surrounding environment,” says Alex Webb, project leader. “Inhibiting photosynthesis slowed the plant’s internal clock by between two and three hours.”

He believes that signals from sugar metabolism and light levels work together to set the time. But many mysteries remain, including how the internal clocks in individual cells are co-ordinated across the whole plant.

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Rare diseases targeted in mass DNA screen

Chain reactions: The UK’s largest DNA sequencing project is to profile 10,000 people with rare diseases©Dreamstime

Chain reactions: The UK’s largest DNA sequencing project is to profile 10,000 people with rare diseases

Britain’s most extensive DNA sequencing project is getting under way in Cambridge, with the aim of reading the genomes of 10,000 people with rare genetic diseases. That will involve analysing 30 trillion “letters” of genetic code.

The project is a pilot for the government’s £100m plan to sequence the genomes of 100,000 patients in the National Health Service over the next five years. A second pilot, focusing on cancer genomes, will also start soon.

John Bradley, director of the National Institute for Health Research, Cambridge Biomedical Research Centre, says the rare genetic diseases project “will bring enormous improvements to the care of patients. It will shorten the gap between the first signs of ill-health in a person and provide a conclusive diagnosis by using the power of modern DNA sequencing methods.”

Cambridge university and the NHS will collaborate on the pilot with Genomics England, the state-owned company set up in July to deliver the 100,000 genome programme, and Illumina, a US-based developer of DNA sequencing machines that use technology developed at Cambridge.

The project is intended both to generate new data for research and to benefit individual patients by cutting short the long search for a cause of their disease. There are an estimated 7,000 rare diseases, which will affect 3.5 million people in Britain at some point in their life.

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