Scientists know this because they have examined 1.5-million-year-old fossils they unearthed and have concluded they represent the first example of two sets of hominin footprints made about the same time on an ancient lake shore. The discovery will provide more insight into human evolution and how species cooperated and competed with one another, the scientists said.

“Hominin” is a newer term that describes a subdivision of the larger category known as hominids. Hominins includes all organisms, extinct and alive, considered to be within the human lineage that emerged after the split from the ancestors of the great apes. This is believed to have occurred about 6 million to 7 million years ago.

The discovery, published today in Science offers hard proof that different hominin species lived contemporaneously in time and space, overlapping as they evaded predators and weathered the challenges of safely securing food in the ancient African landscape. Hominins belonging to the species Homo erectus and Paranthropus boisei, the two most common living human species of the Pleistocene Epoch, made the tracks, the researchers said.

“Their presence on the same surface, made closely together in time, places the two species at the lake margin, using the same habitat,” said Craig Feibel, an author of the study and a professor in the Department of Earth and Planetary Sciences and Department of Anthropology in the Rutgers School of Arts and Sciences.

Feibel, who has conducted research since 1981 in that area of northern Kenya, a rich fossil site, applied his expertise in stratigraphy and dating to demonstrate the geological antiquity of the fossils at 1.5 million years ago. He also interpreted the depositional setting of the footprint surface, narrowing down the passage of the track makers to a few hours, and showing they were formed at the very spot of soft sediments where they were found.

If the hominins didn’t cross paths, they traversed the shore within hours of each other, Feibel said.

While skeletal fossils have long provided the primary evidence for studying human evolution, new data from fossil footprints are revealing fascinating details about the evolution of human anatomy and locomotion, and giving further clues about ancient human behaviors and environments, according to Kevin Hatala, the study’s first author, and an associate professor of biology at Chatham University in Pittsburgh, Pa.

“Fossil footprints are exciting because they provide vivid snapshots that bring our fossil relatives to life,” said Hatala, who has been investigating hominin footprints since 2012. “With these kinds of data, we can see how living individuals, millions of years ago, were moving around their environments and potentially interacting with each other, or even with other animals. That’s something that we can’t really get from bones or stone tools.”

Hatala, an expert in foot anatomy, found the species’ footprints reflected different patterns of anatomy and locomotion. He and several co-authors distinguished one set of footprints from another using new methods they recently developed to enable them to conduct a 3D analysis.

“In biological anthropology, we’re always interested in finding new ways to extract behavior from the fossil record, and this is a great example,” said Rebecca Ferrell, a program director at the National Science Foundation who helped fund this portion of the research. “The team used cutting-edge 3D imaging technologies to create an entirely new way to look at footprints, which helps us understand human evolution and the roles of cooperation and competition in shaping our evolutionary journey.”

Feibel described the discovery as “a bit of serendipity.” The researchers uncovered the fossil footprints in 2021 when a team organized by Louise Leakey, a third-generation paleontologist who is the granddaughter of Louis Leakey and daughter of Richard Leakey, discovered fossil bones at the site.

The field team, led by Cyprian Nyete, mainly consists of a group of highly trained Kenyans who live locally and scour the landscape after heavy rains. They noticed fossils on the surface and were excavating to try and find the source. While cleaning the top layer of a bed, Richard Loki, one of the excavators, noticed some giant bird tracks, then spotted the first hominin footprint. Leakey coordinated a team in response that excavated the footprint surface in July 2022.

Feibel noted it has long been hypothesized that these fossil human species coexisted. According to fossil records, Homo erectus, a direct ancestor of humans, persisted for 1 million years more. Paranthropus boisei, however, went extinct within the next few hundred thousand years. Scientists don’t know why.

Both species possessed upright postures, bipedalism and were highly agile. Little is yet known about how these coexisting species interacted, both culturally and reproductively.

The footprints are significant, Feibel said, because they fall into the category of “trace fossils” — which can include footprints, nests and burrows. Trace fossils are not part of an organism but offer evidence of behavior. Body fossils, such as bones and teeth, are evidence of past life, but are easily moved by water or a predator.

Trace fossils cannot be moved, Feibel said.

“This proves beyond any question that not only one, but two different hominins were walking on the same surface, literally within hours of each other,” Feibel said. “The idea that they lived contemporaneously may not be a surprise. But this is the first time demonstrating it. I think that’s really huge.”

To build proteins, the cell makes a copy of DNA, called mRNA. Then, another molecule called a ribosome reads the mRNA, translating it into protein. But this step has been a visual mystery: scientists previously did not know how the ribosome attaches to and reads mRNA.

Now, a team of international scientists, including University of Michigan researchers, have used advanced microscopy to image how ribosomes recruit to mRNA while it’s being transcribed by an enzyme called RNA polymerase, or RNAP. Their results, which examine the process in bacteria, are published in the journal Science.

“Understanding how the ribosome captures or ‘recruits’ the mRNA is a prerequisite for everything that comes after, such as understanding how it can even begin to interpret the information encoded in the mRNA,” said Albert Weixlbaumer, a researcher from Institut de génétique et de biologie moléculaire et cellulaire in France who co-led the study. “It’s like a book. Your task is to read and interpret a book, but you don’t know where to get the book from. How is the book delivered to the reader?”

The researchers discovered that the RNAP transcribing the mRNA deploys two different anchors to rope in the ribosome and ensure a solid footing and start of protein synthesis. This is similar to a foreperson at a construction site overseeing workers installing a complex section of the superstructure, confirming in two redundant ways that all the pieces are fastened securely at critical junctures for maximum stability and functionality.

Understanding these fundamental processes holds great potential for developing new antibiotics that target these specific pathways in bacterial protein synthesis, according to the researchers. Traditionally, antibiotics have targeted the ribosome or RNAP, but bacteria often find a way to evolve and mutate to create some resistance to those antibiotics. Armed with their new knowledge, the team hopes to outwit bacteria by cutting off multiple pathways.

“We know there is an interaction between the RNAP, the ribosome, transcription factors, proteins and mRNA,” said U-M senior scientist Adrien Chauvier, one of four co-leaders of the study. “We could target this interface, specifically between the RNAP, ribosome, and mRNA, with a compound that interferes with the recruitment or the stability of the complex.”

The team developed a mechanistic framework to show how the various components of the complex work together to bring freshly transcribed mRNAs to the ribosome and act as bridges between transcription and translation.

“We wanted to find out how the coupling of RNAP and the ribosome is established in the first place,” Weixlbaumer said. “Using purified components, we reassembled the complex — 10-billionth of a meter in diameter. We saw them in action using cryo-electron microscopy (cryo-EM) and interpreted what they were doing. We then needed to see if the behavior of our purified components could be recapitulated in different experimental systems.”

In more complex human cells, DNA resides in the walled-off nucleus, where RNAP serves as the “interpreter,” breaking down genetic instructions into smaller bites. This dynamo of an enzyme transcribes, or writes, the DNA into mRNA, representing a specifically selected copy of a small fraction of the genetic code that is moved to the ribosome in the much “roomier” cytoplasm, where it is translated into proteins, the basic building blocks of life.

In prokaryotes, which lack a distinct nucleus and internal membrane “wall,” transcription and translation happen simultaneously and in close proximity to each other, allowing the RNAP and the ribosome to directly coordinate their functions and cooperate with each other.

Bacteria are the best-understood prokaryotes, and because of their simple genetic structure, provided the team with the ideal host to analyze the mechanisms and machinery involved in the ribosome-RNAP coupling during gene expression.

The researchers employed various technologies and methodologies per each lab’s specialty — cryo-EM in Weixlbaumer’s group, and the Berlin group’s in-cell crosslinking mass spectrometry carried out by Andrea Graziadei — to examine the processes involved.

With expertise in biophysics, Chauvier and Nils Walter, U-M professor of chemistry, biophysics, utilized their advanced single molecule fluorescence microscopes to analyze the kinetics of the structure.

“In order to track the speed of this machinery at work, we tagged each of the two components with a different color,” Chauvier said. “We used one fluorescent color for the nascent RNA, and another one for the ribosome. This allowed us to view their kinetics separately under the high-powered microscope.”

They observed that the mRNA emerging from RNAP was bound to the small ribosomal subunit (30S) particularly efficiently when ribosomal protein bS1 was present, which helps the mRNA unfold in preparation for translation inside the ribosome.

The cryo-EM structures of Webster and Weixlbaumer pinpointed an alternative pathway of mRNA delivery to the ribosome, via the tethering of RNA polymerase by the coupling transcription factor NusG, or its paralog, or version, RfaH, which thread the mRNA into the mRNA entry channel of the ribosome from the other side of bS1.

Having successfully visualized the very first stage in establishing the coupling between RNAP and the ribosome, the team looks forward to further collaboration to find out how the complex needs to rearrange to become fully functional.

“This work demonstrates the power of interdisciplinary research carried out across continents and oceans,” said Walter.

Huma Rahil, a doctoral student in the Weixlbaumer lab, and Michael Webster, then a postdoctoral fellow in the lab and now of The John Innes Centre in the United Kingdom, co-led the paper as well.

“We saw that transgender men treated with testosterone increased their muscle volume by an average of 21 percent over six years, but also that the amount of abdominal fat increased by 70 percent,” says Tommy Lundberg, docent at the Department of Laboratory Medicine, Karolinska Institutet. “In addition, they had more liver fat and higher levels of ‘bad’ LDL cholesterol, which may increase the risk of cardiovascular disease.”

The researchers followed 17 adult transgender men and 16 transgender women who were prescribed treatment with testosterone and oestrogen, respectively. They used magnetic resonance imaging (MRI) to map body composition and measured metabolic risk factors via blood tests, blood pressure and vascular stiffness. The scans were conducted before the start of hormone therapy, after one year and after five to six years.

The results show that long-term hormone therapy leads to several major changes in both body composition and metabolic risk factors, particularly in transgender men. The changes in fat volumes continued over time, while the greatest changes in muscle mass and strength occurred after just one year of treatment.

“Previous studies in this area have been relatively short-term, up to two years,” explains Tommy Lundberg. “Our results show that it is important to continue monitoring the long-term health effects of hormone therapy in transgender individuals to prevent cardiovascular disease and other health issues.”

In transgender women receiving oestrogen treatment, the changes were not as pronounced. Their muscle volume decreased by an average of seven percent after five years of treatment, whereas muscle strength remained unchanged. The transgender women increased their total fat volume but gained less abdominal fat.

Tissue samples from muscle, fat and skin were also taken as part of the study. The next step is to analyse these tissue samples to understand the interaction between genetic sex and sex hormones. The researchers are investigating, among other things, how hormone treatment affects skeletal muscle gene expression and the mechanisms behind changes in adipose tissue.

“In addition to the health aspects, our research contributes to increased knowledge about reasonable expectations of the masculinising and feminising effects of sex hormone treatment,” says Tommy Lundberg. “However, some of the changes were relatively modest and should raise caution regarding expectations of long-term and large changes in this patient group.”

The research was funded by Region Stockholm, the Thuring Foundation, the 1.6 Million Club, the Centre for Innovative Medicine at Karolinska Institutet, the Swedish Research Council, the Swedish Medical Association, the Novo Nordisk Foundation and the European Foundation for Studies of Diabetes.

Two of the co-authors are employed by AMRA Medical AB. Tommy Lundberg has been compensated for expert opinions on aspects related to skeletal muscle changes in transgender individuals and reimbursed for travelling to give lectures on the same topic.

In recent years, TNT has started to be replaced with DNAN, but until now very little was known about how this substance impacts the environment and how long it can remain in the soil.

Researchers at the University of York have been studying the environmental impact of the explosive, TNT, for more than a decade. They have shown that the chemical compound, which is used by the military around the world, remains in the roots of plants where it inhibits growth and development.

Now a new study, led by Professor Neil Bruce at the University of York’s Department of Biology and Director of the Centre for Novel Agricultural Products (CNAP), however, has shown that DNAN has similar effects to TNT, but accumulates throughout the plant and lingers for longer.

Professor Neil Bruce said: “Similarly to TNT, DNAN reacts with a key plant enzyme, generating reactive superoxide, which is highly damaging to cells. Over the course of our research we have genetically engineered plants to successfully detoxify land contaminated with munitions.

“Unfortunately DNAN is a very different story to TNT, as it accumulates in the above ground parts of the plant. While plants can use natural processes to reduce the toxicity of TNT, our studies found that plants appear to have no natural way of fighting off the toxic effects of DNAN, meaning that it persists in the plant and is toxic at much lower concentrations.”

Researchers warn that as DNAN is present throughout the plant and not just the root system, as is the case with TNT, there is a greater risk of animals eating the infected plant, introducing the toxin into the food chain.

In previous studies by the York team, genetically modified grass was grown on land contaminated with military explosives, which successfully degraded contaminants to non-detectable levels in their plant tissues, but as yet there is currently no such method to remove or reduce DNAN.

The US is estimated to have over 10 million hectares of military land contaminated with constituents of explosives and the US government estimates that remediation of unexploded ordinances on US military training ranges alone will cost $16-165 billion.

Dr Liz Rylott, co-author of the study from the University of York’s Department of Biology, said: “Recent years have seen an escalation in military explosives due to global conflicts, and so we are potentially looking at vast scales of pollution, which means there is an urgent need, and interest in, developing sustainable plant-based remediation strategies.

“We also don’t know what the limits of DNAN toxicity are in humans, so our hope is that our latest research will highlight that more work is urgently needed to understand its effects.”

This research, published in the journal Nature Plants, was funded by the Strategic Environmental Research and Development Program (SERDP) of the U.S. Department of Defense and was in collaboration with researchers at the U.S. Army Engineer Research and Development Center (ERDC), U.S. Army Corps of Engineers.

Existing research shows that natural sounds, like birdsong, can lower blood pressure, heart, and respiratory rates, as well as self-reported stress and anxiety. Conversely, anthropogenic soundscapes, like traffic or aircraft noise, are hypothesized to have negative effects on human health and wellbeing in a variety of ways.

In the new study, 68 student volunteers listened to three 3-minute soundscapes: a nature soundscape recorded at sunrise in West Sussex, U.K., the same soundscape combined with 20 mile per hour road traffic sounds, and the same soundscape with 40 mile per hour traffic sounds. General mood and anxiety were assessed before and after the soundscapes using self-reported scales.

The study found that listening to a natural soundscape reduced self-reported stress and anxiety levels, and also enhanced mood recovery after a stressor. However, the benefits of improved mood associated with the natural soundscape was limited when traffic sounds were included. The natural soundscape alone was associated with the lowest levels of stress and anxiety, with the highest levels reported after the soundscape that included 40 mile per hour traffic.

The authors conclude that reducing traffic speed in urban areas might influence human health and wellbeing not only through its safety impacts, but also through its effect on natural soundscapes.

The authors add: “Our study shows that listening to natural soundscapes can reduce stress and anxiety, and that anthropogenic sounds such as traffic noise can mask potential positive impacts. Reducing traffic speeds in cities is therefore an important step towards more people experiencing the positive effects of nature on their health and wellbeing.”