Bear teeth break free – Researchers discover the origin of unusual bear dentition

Lower jaw of a polar bear
The polar bear has a second molar that is only slightly larger than the first. Although the polar bear is a carnivore, it is descended from the omnivorous brown bear. 
Photo Credit: © Katja Henßel, SNSB

Mammalian teeth show an astonishing diversity that has developed over 225 million years. One approach to describing the development of mammalian teeth is the so-called “Inhibitory Cascade Model”, short ICM. The ICM describes the growth pattern of molars in the lower jaw. According to the model, the following applies to many mammals: The front molars in the lower jaw influence the growth of all the teeth behind them. 

Certain molecules inhibit or activate tooth growth in the animal's dentition according to the same pattern. Which molars become small or large depends on the size of the first molar, which depends on the animal's diet. In carnivorous mammals, the first molar is usually larger than the third. In herbivores, it is the other way around: the first molar is small, while the third is large. 

Ecological winners: Why some species dominate the planet

A new study sheds light on why some species seem to thrive nearly everywhere, while others are rare and have very limited ranges. Pictured is the boojum tree (Fouquieria columnaris), native only to a few desert regions in Mexico's Gulf of California. 
Photo Credit: Daniel Stolte

Few ideas in science have been tested and confirmed as thoroughly as evolution by natural selection. 160 years ago, Charles Darwin proposed the theory of evolution by natural selection after observing organisms that had developed highly specialized traits to better survive or reproduce in their environments. Whether the same process can explain global patterns of biodiversity, however – why most species are restricted to certain environments while a few outliers seem to be found everywhere – remains largely uncertain.

"We still are not exactly sure why most species are confined to narrow ranges, while only a few thrive nearly everywhere," said Brian Enquist, professor in the University of Arizona Department of Ecology and Evolutionary Biology and senior author of a new study providing the strongest global evidence yet that abundant plant species became so dispersed over time because of their ability to tolerate diverse climates.

Evolutionary Biology: In-Depth Description

Image Credit: Scientific Frontline / stock image

Evolutionary Biology is the sub-discipline of biology that studies the evolutionary processes that produced the diversity of life on Earth, starting from a single common ancestor. These processes include natural selection, common descent, and speciation. It serves as the unifying theory of the biological sciences, providing a framework that explains the unity and diversity of organisms by investigating the changes in the heritable traits of biological populations over successive generations.

Human biology is ill-adapted to modern cities

A new study has found that modern cities are having a huge impact on our health and wellbeing.
Photo Credit: Patrick Robert Doyle

Researchers from Loughborough University and the University of Zurich found that rapid industrialization has reshaped human habitats so dramatically that our biology may no longer be able to keep up. 

The paper, published in Biological Reviews, highlights that densely populated, polluted, and industrialized environments are impairing core biological functions essential for survival and reproduction (i.e., the ‘evolutionary fitness’ of our species). 

The world’s oldest RNA extracted from woolly mammoth

“Such studies could fundamentally reshape our understanding of extinct megafauna as well as other species, revealing the many hidden layers of biology that have remained frozen in time until now”, says postdoc at the University of Caopenhagen, Emilio Mármol.
Image Credit: Scientific Frontline / stock image

Scientists have taken an important step closer to understanding the mythical mammoths that roamed the Earth thousands of years ago. 

For the first time ever, a research team has succeeded in isolating and sequencing RNA molecules from woolly mammoths dating back to the Ice Age. These RNA sequences are the oldest ever recovered and come from mammoth tissue preserved in the Siberian permafrost for nearly 40,000 years. The study, published in the journal Cell, shows that not only DNA and proteins, but also RNA, can be preserved for very long periods of time, and provide new insights into the biology of species that have long since become extinct. 

A new theory of molecular evolution

Evolutionary biologist Jianzhi Zhang
Photo Credit: Courtesy of University of Michigan

For a long time, evolutionary biologists have thought that the genetic mutations that drive the evolution of genes and proteins are largely neutral: they’re neither good nor bad, but just ordinary enough to slip through the notice of selection.

Now, a University of Michigan study has flipped that theory on its head.

In the process of evolution, mutations occur which can then become fixed, meaning that every individual in the population carries that mutation. A longstanding theory, called the Neutral Theory of Molecular Evolution, posits that most genetic mutations that are fixed are neutral. Bad mutations will be quickly discarded by selection, according to the theory, which also assumes that good mutations are so rare that most fixations will be neutral, says evolutionary biologist Jianzhi Zhang.

The U-M study, led by Zhang, aimed to examine whether this was true. The researchers found that so many good mutations occurred that the Neutral Theory cannot hold. At the same time, they found that the rate of fixations is too low for the large number of beneficial mutations that Zhang’s team observed.

To resolve this, the researchers suggest that mutations that are beneficial in one environment may become harmful in another environment. These beneficial mutations may not become fixed because of frequent environmental changes. The study, supported by the U.S. National Institutes of Health, was published in Nature Ecology and Evolution.

Extensive dog diversity millennia before modern breeding practices

Photograph of a modern dog skull used for the photogrammetric reconstruction of 3D models in the study.
Photo Credit: C. Ameen / University of Exeter

A groundbreaking archaeological study has revealed when domestic dogs first began to show the remarkable diversity that characterizes them today. By applying cutting-edge shape analysis to hundreds of archaeological specimens spanning tens of thousands of years, researchers have traced the emergence of distinct dog forms deep into prehistory pinpointing the moment dogs began to diversify in size and shape – at least 11,000 years ago. 

These findings challenge long-standing assumptions that canine diversity is largely a recent phenomenon shaped by selective breeding which started with the Victorian Kennel Clubs. Instead, the study demonstrates that significant variation in skull shape and size among domestic dogs was already present thousands of years ago, soon after their divergence from wolves. 

How fishes of the deep sea have evolved into different shapes

The silvery color of the hatchetfish, which lives in the water column of the deep sea, provides camouflage in dimly lit portions of the ocean.
Photo Credit: Chris Martinez

Fish species living in the deep sea feature a surprisingly large range of body shapes that evolved in different ways and at different rates depending on where the fishes live in the ocean, new research shows. 

Overall, the analysis of nearly 3,000 species showed more diversity of body types among the pelagic fishes, those that swim in open water, than among the benthic species spending their life on the ocean floor. Pelagic fish body types span from the round anglerfish to skinny eels, while benthic fishes generally share a common elongated, tapered shape. 

“We found that evolution pushes and pulls fish body shape in different directions depending on whether they’re benthic or pelagic,” said lead study author Elizabeth Santos, assistant professor of evolution, ecology and organismal biology at The Ohio State University. 

“We talk about the deep sea as if it is sort of all one thing, when really it is not – it is actually quite diverse,” she said. “There are very different types of environments in the deep sea that have their own different effects on evolution.” 

Variety of animals evolved similar genetics solutions to survive on land, study finds

Transition from water to land 
Image Credit: Dinghua Yang

Animals from completely different branches of the tree of life such as insects, worms and vertebrates independently evolved similar genetic solutions to survive on land, according to a new study from researchers at the University of Bristol and University of Barcelona. 

The research, published in Nature suggests that some adaptations are so essential that environmental challenges make evolution predictable.  

The researchers decoded the genetic basis of one of evolution’s more extraordinary innovations – the transition from water to land. 

Researchers discover enlarged areas of the spinal cord in fish, previously found only in four-limbed vertebrates

Zebrafish at the Laboratory of Fish Biology in Nagoya University Researchers discovered that zebrafish have enlarged areas of the spinal cord, previously believed to exist only in four-limbed vertebrates.
 Photo Credit: Naoyuki Yamamoto

Four-limbed vertebrates, known as tetrapods, have two enlarged areas in their spinal cords. The two enlargements have a correlation with the forelimbs and hind limbs, respectively. These enlargements are thought to be caused by the complex muscular system and the rich sensory networks supplying nerves to the limbs.

Meanwhile, it was long thought that fish had no enlarged areas in their spinal cords due to the absence of limbs. However, a recent study by scientists from Nagoya University in Japan has revealed that zebrafish, in fact, have enlarged areas in their spinal cords, although these areas are not visible to the naked eye.

"We thought that fish also have spinal enlargements because they have paired pectoral and pelvic fins, which correspond to forelimbs and hind limbs in tetrapods, respectively," said  Naoyuki Yamamoto, a professor at Nagoya University's Graduate School of Bioagricultural Sciences and the lead author of the study.