A model of a homo sapien..
(photo credit: Wikimedia Commons)
When somebody is called a “Neanderthal,” it is more an insult than a compliment, as it suggests that the person combines a low IQ with a habit of using brute force. In fact, the remnants of these archaic humans who existed before modern man (Homo sapiens) are being studied intensively by scientists to learn more about ourselves.
Neanderthals and the recently discovered Denisovans of Siberia were two of several extinct types of humans with whom we lived side by side, but only H. sapiens survived. What was it in our genetic makeup that gave us the advantage? The answer lies in changes in the way our genes work, according to scientists at the Hebrew University of Jerusalem and colleagues in Europe.
While genetics deals with the DNA sequence itself, and its heritable mutations, epigenetics deals with heritable traits that are not caused by such mutations.
Rather, chemical modifications to the DNA can efficiently turn genes on and off without changing the sequence. This epigenetic regulatory layer controls where, when and how genes are activated and is believed to be behind many of the differences between human groups. Very little is known about humans’ unique epigenetic makeup, but it is exactly such changes that may have shaped our own species.
In an article just published in Science, Dr. Liran Carmel, Prof. Eran Meshorer and David Gokhman of HU’s Alexander Silberman Institute of Life, along with scientists from Germany and Spain, have for the first time reconstructed the epigenome of the Neanderthal and the Denisovan.
Then, by comparing this ancient epigenome with that of modern humans, they identified genes whose activity had changed only in our own species during our most recent evolution. Among those genetic pattern changes, many are expressed in brain development. The team also noted numerous changes in the immune and cardiovascular systems, with the digestive system remaining relatively unchanged.
On the negative side, the researchers found that many of the genes whose activity is unique to modern humans are linked to diseases like Alzheimer’s disease, autism and schizophrenia – suggesting that these recent changes in our brain may underlie some of the psychiatric disorders that are so common in humans today.
By reconstructing how genes were regulated in the Neanderthal and the Denisovan, the researchers provide the first insight into the evolution of gene regulation along the human lineage and open a window to a new field that allows the study of gene regulation in species that went extinct hundreds of thousands of years ago.
MIGHTY MITE IS WORLD’S FASTEST LAND ANIMAL
Relative to its size, a Southern California mite runs faster than any other animal. It also thrives in temperatures that would kill most other animals. Although the mite, named Paratarsotomus macropalpis, is no bigger than a sesame seed, it was recently recorded running at up to 322 body lengths per second, a measure of speed that reflects how quickly an animal moves relative to its body size. The previous record-holder, the Australian tiger beetle, tops out at 171 body lengths per second.
By comparison, a cheetah running at about 100 kilometers per hour attains only about 16 body lengths per second. Extrapolated to the size of a human, the mite’s speed is equivalent to a person running roughly 2,000 kilometers per hour.
A California college student named Samuel Rubin, who spent a summer chasing down the remarkable mites, says the discovery is exciting not only because it sets a new world record but also for what it reveals about the physiology of movement and the physical limitations of living structures.
“It’s so cool to discover something that’s faster than anything else, and just to imagine, as a human, going that fast compared to your body length is really amazing,” said the physics major at Pitzer College who led much of the fieldwork to document the mite’s movements. “But beyond that, looking deeper into the physics of how they accomplish these speeds could help inspire revolutionary new designs for things like robots or biomimetic devices.”
Rubin’s advisor, biology Prof. Jonathan Wright at Pomona College, became interested in the mites while studying the effect of muscle biochemistry on how quickly animals can move their legs. But it wasn’t until Rubin and other students documented the mites’ running speeds in their natural environment that the research team knew they had found a new world record.
Both relative speed and stride frequency increase as animals get smaller, and in theory, muscle physiology should at some point limit how fast a leg can move.
“We were looking at the overarching question of whether there is an upper limit to the relative speed or stride frequency that can be achieved,” said Wright. “When the values for mites are compared with data from other animals, they indicate that, if there is an upper limit, we haven’t found it yet.”
The mite is local to southern California and is often found running along rocks or sidewalks. Although it was first identified in 1916, little is known about its habits or food sources. The research team used high-speed cameras to record the mites’ sprints in the laboratory and in their natural environment.
“It was actually quite difficult to catch them, and when we were filming outside, you had to follow them incredibly quickly as the camera’s field of view is only about 10 centimeters across,” said Rubin.