The human pelvis is a defining feature of our species. We couldn't give birth to babies with big brains without it. A new study of human embryos has identified hundreds of genes and regulatoryRNA regions that play a role in the transformation of the pelvis into a human. The hallmarks of strong natural selection are found in many of them.
The study uses all the bells and whistles of state-of-the-art-analysis, according to an anthropologist at the University of Zrich. She supports the idea that evolution can produce new physical features by acting on genetic switches. She says that such predictions are easy to state but hard to demonstrate.
The pubis and ischium are the two fused bones that make up the birth canal in a primate. There are relatively narrow birth canals for great apes that lie flat against the back of them. Humans have short and rounded ilia. There are attachment points for the muscles that make upright walking more stable and a wider birth canal for big brained babies. The 4.4 million-year-old hominin Ardipithecus ramidus, which had slightly turned-out ilia, is thought to have had at least occasionally.
It was not clear when and how those features took shape in humans. The curved, basinlike shape is one of the key human pelvic features. When the pelvis has not yet turned to bone, Capellini wondered if they would emerge earlier.
Women who had legally terminated their pregnancies consented to the researchers examining the 4- to 12-week-old embryos. Around the 6 to 8 week mark, the ilium begins to form and then rotates into its basinlike shape. As the embryo starts to ossify into bone, Capellini's team found that the cartilage stage in the pelvis continues for several more weeks, giving the developing structure more time to curve and rotation. Cartilage is taking that shape and is not bones.
The researchers were able to see which genes were active at different stages of development by taking theRNA from different parts of the embryo. They identified hundreds of human genes that were found in certain parts of the body during the first few weeks of the baby's life. There were 260 genes in the ilium. Many of the genes that are down regulated are involved in turning the cartilage to bone, while many of the genes that are up regulated are involved in keeping the ilium in a cartilaginous stage.
Thousands of genetic on/off switches seem to be involved in shaping the human pelvis, according to a study. Since our species split from our common ancestor with Chimpanzees, the stretch of DNA within those switches appears to have evolved quickly. The regulatory bits in the ilium are pretty much the same as they were in the past. It's a sign that natural selection puts intense pressure on the ilium to develop in a specific way.
The origin of bipedalism in our genome is being pointed out by Capellini.
According to Martin Husler, an anthropologist at UZH, the findings offer an impressive look into some of the pelvic changes that make us humans. Future work comparing human embryo with other primate embryo would allow for a better look at how natural selection shaped the human pelvis.
The emerging understanding could help scientists figure out treatments for hip joint disorders or predict the outcome of a baby's birth. Hip dysplasia and hip arthritis can be caused by deviations from the genetic program identified by Capellini. I hope that it will have a big impact on making peoples lives better. It would be huge to connect paleoanthropology with reality.
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