Lankan scientist plays key role in Harvard study of ancient genetic changes
View(s):Lankan scientist Dr Gayani Senevirathne has played a key role in a Harvard University study that has uncovered the genetic changes which enabled humans to walk on two legs – a discovery described as a turning point in understanding human evolution.
The research, published this week in the journal Nature, focuses on the pelvis, the central structure that supports the body, anchors muscles used for walking, and forms the birth canal. While it is a bone we use every day without thinking, scientists have long struggled to explain how the human pelvis became so different from that of our closest relatives, the great apes.
Dr Senevirathne, working with Harvard developmental geneticist Professor Terence Capellini, traced the transformation of the pelvis through painstaking comparisons of embryos and foetuses from humans and other primates. Her work revealed two major genetic shifts that reshaped the ilium – the largest bone of the pelvis and the one felt when a hand is placed on the hip.
The first shift took place between five and eight million years ago, around the time humans diverged from chimpanzees and other African apes. In human embryos, the growth plate of the ilium rotates 90 degrees during the seventh week of development. This flip changes the orientation of the pelvis, allowing it to grow wide and bowl-shaped rather than tall and narrow. The broader shape provided the muscle attachments needed for balance and stability while walking on two legs.
The second transformation came about two million years ago, as human brain size began to increase rapidly. The ilium in humans remains cartilaginous for much longer than in other primates – 15 to 16 weeks more – before hardening into bone. This unusual delay allowed the pelvis to remain wide enough to maintain efficient upright walking while also enlarging the birth canal, making it possible to deliver babies with much bigger heads.
Together, these two changes gave rise to the hallmark features of human locomotion while also accommodating the evolutionary pressures of larger brains.
The Harvard team identified more than 300 genes involved in shaping the pelvis. Rather than a single “gene for walking”, the study shows that an entire network of genetic switches works in unison during foetal development to produce the distinctive human pelvic structure.
Fossil evidence supports the genetic findings. The 4.4 million-year-old Ardipithecus ramidus skeleton from Ethiopia shows the beginnings of a wider pelvis suited for occasional bipedalism. By the time of Australopithecus afarensis, the species of the famous 3.2 million-year-old “Lucy” skeleton, the ilium already had the bowl-like shape seen in modern humans, indicating that upright walking was well established.
Professor Capellini has described the change as a “complete mechanistic shift” in human history, without which walking on two legs – and later, the growth of large brains – would not have been possible.
For Dr Senevirathne, the discovery was the result of years of detailed, and often difficult, research. She travelled to museums in the United States and Europe to locate and study rare primate embryos, many over a century old, and built three-dimensional models to compare pelvic growth across species.
Colleagues have described her work as central to the breakthrough. In one instance, she drove from Boston to New York at dawn to collect crates of 100-year-old lemur embryo slides – the kind of meticulous effort that made it possible to see the developmental patterns hidden in long-forgotten specimens.
Her contribution highlights the role of Sri Lankan scientists in global research. Few from the island have been at the forefront of studies published in Nature, one of the world’s most prestigious scientific journals.
Despite the scale of the discovery, the project itself faces uncertainty. Earlier this year, the Trump administration cut billions of dollars in research funding to Harvard University, including the grant that supported the pelvis study. Dr Capellini’s team was only two years into a five-year plan when the funding was withdrawn.
For Dr Senevirathne, the findings also demonstrate the value of perseverance in science. What began with a search for century-old embryos has ended in a discovery that redefines one of the central events in human history.
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