A 555-million-year-old worm had a predilection for turning right, possibly indicating the oldest known example of handedness.

Although these worms lacked limbs and so couldn’t be considered left- or right-handed in the way that we understand, the development of a tendency to favour one side over another is evidence of an advanced nervous system.

It remains a feature of free-living mobile life today, but until this discovery, it wasn’t thought to have emerged until the Cambrian Period, which began around 541 million years ago.

at the American Museum of Natural History in New York and his colleagues analysed 100 fossil specimens of a small flatworm-like creature, Spriggina floundersi, collected in South Australia over recent decades.

These animals lived during the Ediacaran Period, when multicellular life first became widespread. It preceded the Cambrian explosion, when animal life diversified dramatically and many groups of animals first appeared.

Spriggina lived in what was, half a billion years ago, a shallow ocean and is thought to have foraged on or close to the seafloor, moving by wriggling to the left or right.

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“We have around 50 specimens of Spriggina that are clearly bent,” says Evans. Twice as many of the fossilised worms are bent to the left than to the right, he says. This means the creature itself bent to the right, as the specimens are mirror-image impressions of the animals, made when storms buried them in sand.

“This appears to be statistically significant and matches what biologists find when they study handedness in different animals today,” says Evans. “Some specimens have multiple bends to both the right and left, suggesting that they all could bend both ways, which makes sense if you don’t want to be stuck moving in a circle.”

While the majority seem to demonstrate right-handedness, it is hard to tell if any were left-handed, he says. “I imagine it’s like taking a picture of 100 people waving with one hand today. You would likely be able to count that more people are waving with their right hand, but you wouldn’t be able to tell who is right- or left-handed.”

Discoveries like this demonstrate that many foundational characteristics that are common to a variety of animals today, such as the ability to move around, bilateral symmetry and handedness, evolved in the Ediacaran, says Evans.

In the Cambrian, organisms built on that foundation to become more complex, for example adding legs to move more efficiently, becoming “less alien and more like the major groups of animals we know today”, says Evans. “This is cool because it suggests that, while the Cambrian was an amazing time in animal evolution, those organisms didn’t just come out of nowhere: they built on the foundations established in the Ediacaran.”

“The presence of handedness in any kind of functional asymmetry, really deep into the fossil record, gives us important and interesting information about how these behaviours have evolved and how deeply in time they emerged,” says at Flinders University in Adelaide, Australia.

Bees seem to show when they are pleased and like something, rather than just needing it, in one of the strongest signs yet that insects have subjective experiences.

In recent decades, it has become clear that bees are capable of more complex behaviours than we previously thought, such as counting and demonstrating a sense of rhythm. But discerning whether they have inner states akin to our emotions is more difficult. For one thing, insects don’t have the flexible facial musculature of mammals, which we use to communicate our feelings.

“How can we get any behavioural readout of these insects with a hard body and their mask of a face,” asks at Macquarie University in Sydney, Australia. “Do bees have any sort of inner state whatsoever?”

To solve the mystery, Barron and his colleagues ran a series of experiments involving buff-tailed bumblebees (Bombus terrestris).

First, the team offered the bees a water droplet containing sugar, along with others that contained salt and quinine, while filming them using high-resolution video.

After tasting the sweet liquid, the bees repeatedly stuck out their glossa, which is a hairy tongue that they use to lap up nectar in flowers. After tasting the salty and bitter samples, the bees wiped their mouths and shook their heads.

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However, both responses may have just been a reaction to the different chemicals, rather than a sign of enjoyment or displeasure, says Barron.

Next, the researchers reduced the concentration of the sugar and mixed it with a small amount of salt, resulting in a dramatic reduction of the glossa protrusions. Then they exposed the bees to 40°C (104°F) temperatures to dehydrate them, after which, when the bees were offered salty droplets, the bees repeatedly protruded their glossa.

“If I just handed you an electrolyte drink right now, you’d probably think, ‘well, that actually tastes pretty foul’,” says Barron. “But if you had just come back from a long run and I handed you an electrolyte drink, you’d think, ‘that’s fantastic’. It’s because your internal state has changed, and that internal state is changing your evaluation of things – that’s what we think we’re seeing in the bees.”

For the final part of their experiment, the researchers wanted to determine what would happen if they meddled with the chemistry that, in mammals, underpins appetite and the enjoyment of food.

When the bumblebees were treated with dopamine, which in mammals affects the motivation to seek food, their glossa protrusions didn’t increase, suggesting that although they had greater desire, their enjoyment “tell” – tongue protrusions – didn’t change.

But when the bees were treated with endocannabinoids, which increases the “liking” of food in mammals, it led to an increase in their glossa protrusions.

“What this is showing us is that even from an animal like a bee, there is some sort of inner life for that insect,” says Barron. “There’s something going on. It’s evaluating its world. It’s experiencing its world and it’s not a robotic entity running on a program.”

at the California Institute of Technology says the research is “an important and innovative study on a difficult topic”. “The evidence presented in the paper shows that the bees represent the value of the taste stimuli in a flexible manner,” he says. But it is unclear whether the experiments demonstrate pleasure as we know it.

“The idea that facial expressions are literally constitutive of emotions is clearly not the case. Actors can fake them, and people whose faces are paralysed still have emotions,” he says. “I think we should conclude that bees have bee emotions, not mammal emotions.”

at the London School of Economics says the study is the first time he has  seen “wanting” and “liking” disentangled in a bee.

“We underestimate insects so much,” he says. “It’s led to a golden age of very charming studies where scientists use modern techniques – sometimes just high-resolution, high-frame-rate video, as in this study – to reveal behaviours people have been missing.”

Childbirth can be extremely challenging for humans – but some other primates may have it even worse. A comprehensive analysis of primate anatomy concludes that many species must squeeze large-headed infants through too-narrow pelvises. The problem may have begun with the very first primates, which lived more than 50 million years ago.

It has been assumed for decades that evolution has left humans with unique childbirth difficulties. The conventional view is that the trouble began when our ancestors first walked on two legs, which required the pelvis to be narrow. A few million years later, hominin brains evolved to be larger and infant heads became bigger – but the pelvis was unable to expand to allow for their easy delivery.

Other primates were thought to have things easier, largely because that was the conclusion of an published by anthropologist Adolph Schultz in the 1940s. Schultz looked at a range of primate species and concluded that in the vast majority, the infant head could fit comfortably through the female pelvis.

But his analysis was flawed, says at University College London. “One of the main problems was that it applied measurements that were originally developed for the human pelvis to all primates,” she says.

Schultz identified landmark points on the human pelvis that define the maximum width and depth of a horizontal plane at the top of the birth canal. He then assumed those same landmarks would define the maximum width and depth of any primate birth canal. They don’t. The human pelvis has a very unusual shape, and when Schultz’s landmarks are mapped onto other primate pelvises, they typically define an inclined plane that sits slightly above the birth canal. This plane overestimates the size of the birth canal, because it is effectively an oblique, oval-shaped slice through a cylinder representing the birth canal.

Torres-Tamayo and her colleagues reassessed birth canal shape in 29 primate species, while also looking at data on newborn-skull size and shape in each species. They concluded that several primates have a pelvis that seems too narrow to give birth. Small primates including bush babies and tamarins have the most severe conflict. In these primates, the newborn’s head is almost twice the size of the birth canal.

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“I was not expecting to have a mismatch in quite such a large number of primates,” says research team member , also at University College London.

Birth difficulties may even be the ancestral condition in primates, says Betti, particularly considering that early primates were small.

“It’s super cool to have such a big sample,” says at the University of Zurich, Switzerland. “These species are doing very different things, living in different niches and they do tend to be quite anatomically diverse.”

Different primates have also found their own solutions to the problem. For instance, the bush babies and tamarins dislocate the bones of the pelvis, temporarily doubling the size of the birth canal. Humans can’t do this, says Betti: it would make walking unbearably painful for a large, bipedal species.

Torres-Tamayo and Betti and their colleagues also found that birth difficulties are much less likely to arise in the great apes, maybe because they are so much larger than the tiny tree-dwelling primates. In this sense, humans are still unique in having birth difficulties, because we are the only large ape with the problem, says Betti.

But Webb isn’t so sure about this point; in a study she and her colleagues published in 2024, they concluded that between the size of the birth canal and the infant’s head. “That discrepancy is strange. It’s probably a reflection of the methods used,” says Webb. “This new paper is providing a really nice incentive for us to revisit our own hypothesis.”

A set of exquisitely preserved 300-million-year-old fossils suggests that early four-limbed vertebrates did not undergo a metamorphosis between their juvenile and adult stages, challenging conventional ideas about the evolution of life on land.

“We have for a very long time assumed that these animals were broadly amphibian-like, and that this life cycle would have bridged the gap between life in the water and life on land,” says at the Field Museum of Natural History in Chicago.

Today’s reptiles, birds, mammals and amphibians belong to a group called tetrapods, which evolved from lobe-finned fish around 390 million years ago. But almost nothing was known about the early developmental stages of these ancestral lobe-finned fish, says at Flinders University in Adelaide, Australia.

Pardo and his colleague , also at the Field Museum, examined a collection of fossils that were unearthed between the 1960s and 1990s at the Mazon Creek fossil site, south-west of Chicago. The preserved animals lived 307 million to 309 million years ago, during the Carboniferous Period.

Embolomeres, which had a body around 2 metres long in adulthood, were the largest tetrapods in the Carboniferous and one of the top predators. They spent most of their time in water, but had small legs with which they could have clambered onto the land.

The fossils included two 2-centimetre-long baby embolomeres, which were so well preserved that the scientists could see soft tissues and even egg yolk.

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In tadpoles, the yolk sac remains inside the body for a few days after hatching as a store of energy. But the young embolomeres had a yolk sac outside the body, similar to the case for some young fish such as lungfish.

Amphibian larvae, such as tadpoles, have external gills that enable them to breathe underwater, but the young embolomeres did not. “The absence of external gills across early development in these animals is the smoking gun,” says Pardo.

The skull and skeleton have “all the important parts seen in an adult embolomere”, says Pardo. The fossils show that embolomeres remained more or less the same from the time they hatched from their eggs until they reached adulthood.

“Human bodies basically work the same way from birth through adulthood, but we get bigger and our proportions change, but we don’t undergo the sort of fast, rapid change you see in a frog or salamander,” says Pardo. “Our fossils show that this sort of life cycle was the norm for our earliest terrestrial ancestors, too.”

Although embolomeres were aquatic, Pardo argues that the evidence available suggests our earliest terrestrial ancestors did not have a tadpole-like stage either. The team also studied the fossil remains of two other early tetrapod species that were alive at the same time and in the same place as the embolomeres.

“None of these show any evidence of a tadpole-like stage,” says Pardo. “Neither do other fishy tetrapod relatives such as early lungfishes and coelacanths. So is it impossible that a tadpole stage showed up somewhere and was subsequently lost? Maybe, but it seems vanishingly unlikely with the data we have.”

This study fills in a much-needed knowledge gap, says Long. “It shows how early tetrapod-like fishes living about 308 million years ago did not need to develop a tadpole phase in order to invade land, as was previously thought by some scientists.”

Fossil hunting in the Australian outback

Join this extraordinary adventure through the heart of Australia’s fossil frontier. Once a shallow inland sea millions of years ago, eastern Australia is now a hotspot for fossils. Over 13 unforgettable days, you’ll travel deep into the outback, tracing the footsteps of prehistoric giants and uncovering the secrets of Earth’s ancient history.

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