Wasous

Populations of indigenous people in southern Africa carry a gene that causes lighter skin, and scientists have now identified the rapid evolution of this gene in recent human history.

San man of Namibia [Credit: Ian Beatty/WikiCommons]

The gene that causes lighter skin pigmentation, SLC24A5, was introduced from eastern African to southern African populations just 2,000 years ago. Strong positive selection caused this gene to rise in frequency among some KhoeSan populations.

UC Davis anthropologist Brenna Henn and colleagues have shown that a gene for lighter skin spread rapidly among people in southern Africa in the last 2,000 years.

This is a "rare example of intense, ongoing adaptation in recent human history and is the first known example of adaptive gene flow at a pigmentation locus in humans," according to the paper published online in the Proceedings of the National Academy of Sciences.

The findings are based on research by multiple scientists. The primary author, Meng Lin, conducted the research as a graduate student at Stony Brook University, working with anthropologist Brenna Henn, now of the University of California, Davis, Genome Center and Department of Anthropology. Lin is now a post-doctoral researcher in genetics at the University of Southern California.

In previous work, the researchers looked at pigmentation variation in two KhoeSan populations from South Africa by performing a genome-wide association analysis in about 450 individuals. They followed up on the top associated gene, SLC24A5, by simulating population histories with and without positive selection. The DNA and pigmentation sampling took place in the Northern Cape of South Africa in the southern Kalahari Desert and Richtersveld regions.

Gene plays a role in lighter skin pigmentation

Individuals who carry two copies of the lighter pigmentation gene are 14 percent lighter-skinned than the population average, the researchers said. The gene SLC24A5 plays a key role in the genetic basis of light skin pigmentation.

While light skin is often associated with European ancestry, even in South Africa, the present-day Khoekhoe and San did not experience enough recent migration to account for the frequency of the gene. Rather, strong positive selection during the past 2,000 years was the only way to explain the current distribution. The gene, which is also present in people from the Near East and eastern Africa, was probably initially brought into the region by only a small number of individuals.

The actual source of the positive selection is not clear. The researchers theorize that a shift from consuming vitamin D-rich marine animals to consuming pasture animals, or a reduction in exposure to ultraviolent rays, might have changed skin pigmentation over time.

"While the biological cause of the selective event merits further investigation, we have demonstrated an unusual rapid case of selection for lighter skin pigmentation based on a recently introduced allele less that 2,000 years ago, the first case of pigmentation adaptation from migration in humans," the paper concludes.

Author: Karen Nikos-Rose | Source: UC Davis [December 10, 2018]

The analysis of the world’s most complete skeleton of an early human ancestor, conducted by a research collaboration involving the University of Liverpool, offers conclusive evidence that human ancestors became efficient upright walkers while they were still substantially tree dwelling animals.

Professor Ronald Clarke with Little Foot [Credit: University of Liverpool]

The first bones of the 3.67 million old skeleton, specimen StW 573 nicknamed ‘Little Foot’, were 12 foot bones and leg bone fragments identified in boxes in the 1990s. The rest of the skeleton has undergone two decades of painstaking excavation, cleaning, restoring and analysis. It was found in a very deep cavern, with the bone embedded in a concrete-like matrix. The bone is very delicate and in some cases literally paper-thin. However, it has given scientists a far greater understanding of how our species evolved.

Limbs intact

The over 90% complete skeleton of an old female, much more than twice as complete as the famous Lucy, and considerably older as well, Little Foot is a member of the genus Australopithecus, a widespread and varied genus of hominins to which Lucy belonged, and which was an early precursor to modern-day Homo sapiens which appeared roughly 300,000 years ago. Little Foot is the first fossil of Australopithecus ever to have been discovered with its limbs intact.

Little Foot’s fossil bones [Credit: Patrick Landmann/Science Photo Library]

The studies support the argument of her discoverer, Professor Ronald Clarke of the University of the Witwatersrand, that there were two species of Australopithecus living at the same time in South Africa’s ‘Cradle of Humankind’, Australopithecus africanus, which was small, like Lucy, and probably primarily tree-dwelling, and Australopithecus prometheus, which was probably just within the range of modern human stature.

Important finding

As part of the study, which has been reported in Nature Science, Professor Robin Crompton, Honorary University of Liverpool Research Associate in Musculoskeletal Biology, and his colleagues analysed how she would have walked.


Professor Crompton, states: “This hominin, for the first time in the fossil record, had longer lower limbs than upper limbs, like ourselves. This is an important finding, as the slightly older hominin Ardipithecus, which came before Australopithecus, had longer arms than legs – more like other great apes such as the gorilla.

“That means she was being selected for long stride length in bipedalism. Moreover, unlike Lucy, ‘Littlefoot’ had a hip joint like our own, able to transmit large forces from the trunk to the leg and vice versa. Although Little Foot’s legs were longer than her arms, they had not yet achieved the great relative leg length found in humans. Thus, she would not have been as good at carrying objects as we are. However, she would have been much better at climbing trees than modern humans.

“It is most likely that she would have resided in an area that was a mix of tropical rainforest, broken woodland and grassland, through which she would roam around. She would have lived primarily on forest fruits and leaves”

Source: University of Liverpool [December 10, 2018]