A new study finds evidence of an important neural speech pathway in macaques.
- Researchers find traces of something like our arcuate fasciculus in macaque brains.
- Since the last ancestor we shared with macaques was 25-30 million years ago, this would push speech way back.
- The study suggests human speech began in the auditory cortex and eventually extended to include the executive-function areas of the brain.
The arcuate fasciculus and the auditory cortex<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzE3NzAwOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxMjExMzE3NX0.3tVh8sWuOdfsWWxu_an5-opBLdy7ag616NhSrnOsaTU/img.jpg?width=980" id="f2ff0" class="rm-shortcode" data-rm-shortcode-id="491baf85f91e992ac0e2407158520d1e" data-rm-shortcode-name="rebelmouse-image" />
Image source: Human Brain MRI Data and Connectome Atlas /wikimedia<p>The fuss is about a neural pathway in humans called the arcuate fasciculus, or AF, that traverses our prefrontal cortex and frontal lobe. Recent <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3071430/" target="_blank">research</a> suggests it has connections to other brain regions as well.</p><p>"This is a pathway that interconnects brain regions that are important for language. If this pathway or some of these regions it interconnects are damaged because of stroke or brain degeneration a person might immediately (because of stroke) or progressively (because of dementia) lose the ability to understand or to produce language," Petkov tells <em>Newsweek</em>.</p><p>For the study, international teams of European and US scientists pored through new imaging data of humans looking for evidence of this pathway in other regions. They found a segment of it, unexpectedly, in the auditory complexes of both brain hemispheres, though most strongly identifiable in the left one. <a href="https://www.newsweek.com/origin-human-brain-network-language-20-million-years-scientists-1498967" target="_blank">Says</a> Petkov, "To be honest, we were really quite surprised that the auditory system has this privileged pathway to vocal production regions in frontal cortex." He adds, "That in itself tells us that there is something special about this pathway. The link to projection from the auditory system to frontal cortex regions, which in humans supports language, is fascinating."</p>
Not just us<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzE3NzAxMS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxMTk2MjYyN30.ejPIZESh11Q1m5DlyZLvlI1i_TXOCbczHem3zw2Nqkc/img.jpg?width=980" id="3c45b" class="rm-shortcode" data-rm-shortcode-id="5609a51cb22bac3075a6ae59404ff3aa" data-rm-shortcode-name="rebelmouse-image" />
Image source: Steven Diaz/Unsplash<p>Things got even more interesting when Petkov and his colleagues began searching for the AF in apes and monkeys. In their auditory cortexes, too, the researchers saw what appeared to be something similar to, though less distinct than, the human AF. Their interpretation of the finding is that speech may have begun in the auditory cortex and in humans over time spread outward to encompass the prefrontal cortex and frontal lobe whose executive function allowed us to develop basic sound communication into sophisticated speech.</p><p>"Whether monkeys have a homolog (a precursor) of this pathway was highly controversial," says Petkov. "Thinking further about the basis for the controversy, when we started the project we also wondered whether such a pathway in monkeys was missed because scientists had not looked in the correct place. We predicted that a missing correspondence to humans might be hiding, so to say, in the auditory system. So that is where we looked first. The analogy here is that we may have been looking in the wrong place for the missing brain 'fossil.'"</p>
Do macaques talk, then?<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzE3NzAxNS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY2MjQxNTk5Nn0.HqlbLesqREYhFirwH0xOgayYDsd_wqKkomOeQpyxC1o/img.jpg?width=980" id="b54bc" class="rm-shortcode" data-rm-shortcode-id="a377d5fdf6b87df26c682f1a5b77592e" data-rm-shortcode-name="rebelmouse-image" />
Image source: Jonathan Forage/Unsplash<p>Well, in a sense, yes. While we haven't observed words and sentences in these <a href="https://en.wikipedia.org/wiki/Old_World_monkey" target="_blank">Old World monkeys</a>, they do <a href="https://www.nih.gov/news-events/nih-research-matters/hints-language-origin-rhesus-monkey" target="_blank">communicate with vocal sounds and with gestures</a>, signaling information about food and about imminent danger. Other research has identified what appears to be a <a href="https://bigthink.com/robby-berman/researchers-discover-monkeys-have-a-speech-ready-vocal-tract" target="_self">speech-ready vocal tract</a>.</p><p>Finding an AF-like pathway in macaques may not even represent their earliest development, notes Petkov, who points out, "there may be more brain 'fossils' yet to be discovered with even earlier evolutionary origins. Or it may be discovered that the origin of this pathway traces back even further if another brain "fossil" is found."</p>
But/and...<p>Not everyone will be onboard with Petkov's conclusions, which he admits are "highly controversial." Still, if they turn out to be valid, even beyond the "wow" factor, who knows where further identification of AF-related pathways could lead, potentially including new ways to work around interruptions in brain circuitry that may affect patients with speech-based disorders.</p><p>Joint senior author neurologist <a href="https://www.ncl.ac.uk/medical-sciences/people/profile/timgriffiths.html" target="_blank">Timothy Griffiths</a> says, "This discovery has tremendous potential for understanding which aspects of human auditory cognition and language can be studied with animal models in ways not possible with humans and apes. The study has already inspired new research underway including with neurology patients."</p>
Some fish evolved legs and walked onto the land. Right?
Evolution explains how all living beings, including us, came to be. It would be easy to assume evolution works by continuously adding features to organisms, constantly increasing their complexity.
It's possible to seek equality without seeking sameness.
- Males and females as a population, on average, are different. Beyond obvious differences in reproductive systems, research has shown measurable differences between the sexes in areas such as linguistic capabilities.
- Evolutionary biologist Heather Heying argues that while males and females should be equal under the law, that does not mean that their differences should be ignored. "We should seek equality without seeking sameness."
- People should be given the freedom to make choices, not forced to engage in activities in the name of equality.
Not only do these monkeys use tools, they're developing new, better tools to adapt to their environment.
- Archaeologists dug into the ground of an area of a Brazilian national park known to be frequented by capuchin monkeys.
- They found that over the past 3,000 years, the stone tools that the monkeys use have evolved and changed, marking the first time this kind of development has been observed in a non-human species.
- The findings underscore the intelligence of the capuchin monkeys and serve as a parallel to our own development.
Analyzing the stone tools<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTYyODIwNS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY0MzMzNzkzMX0.pzdxXsJleydwNOaqQh7x5Tcdtm0LUHGaw2X7J0mqefs/img.png?width=980" id="551ea" class="rm-shortcode" data-rm-shortcode-id="1d045580de1ba49fe53ce396b3f17970" data-rm-shortcode-name="rebelmouse-image" />
Examples of the capuchin monkeys' stone tools with typical percussive damage.
Photo: Falótico et al., 2019<p>To determine this, the researchers dug several feet down and recovered stones that they referred to as "hammerstones" or "anvils." These could be identified by their sizes, since they tended to be larger than the pebbles naturally found in the ground, and they have small impact marks covering their surfaces. It was clear that these were specifically capuchin tools and not those of ancient humans, since humans tend to use sharpened, knapped stones instead of conveniently shaped natural rocks.</p><p>Then, the researchers radiocarbon-dated the stone tools to determine their age. Altogether, the tools came from four distinct periods in capuchin history, with a maximum age of around 3,000 years. By comparing the periods with the stones' characteristics, the researchers were able to identify what tasks the capuchins were using these tools for. </p><p>The earliest tools were small and covered in many impact marks, suggesting that they were used for processing many small, soft foods, like seeds. Then, the tools grew larger, indicating that the capuchins had shifted their diet to one consisting of hard-shelled nuts and fruits. Beginning about 100 years ago, the stone tools shifted to a moderate size, which modern capuchins use to crack open cashews.</p>
What's the significance?<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="6b9c9913ca1604ed06e34465811b07c8"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/_MgHBvp1uwk?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>It might seem like pounding rocks against rocks can hardly be considered tool use or that the fact that these stones changed size over time isn't significant. However, using rocks to pound things is the first example of <a href="http://humanorigins.si.edu/evidence/behavior/stone-tools/early-stone-age-tools" target="_blank">human tool use</a>, too. What's more, West African chimpanzees have been observed using large, heavy stones to crack tough-shelled nuts and small stones to break softer-shelled nuts, lending credence to the researchers' theory that the size variation of the capuchin stone tools corresponded to a change in diet.</p><p>The real contribution of this study, however, is that it's the first to record an on-going variation in non-human tool use. West African chimps may use different tools for different tasks, but there's no evidence that this has changed over the past few millennia. To Proffitt, this is an exciting find.</p><p>"This capuchin excavation shows that this species of primate in Brazil has its own individual archaeological record," he told <em><a href="https://www.nationalgeographic.com/science/2019/06/capuchin-monkeys-used-stone-tools-3000-years-oldest-outside-africa/" target="_blank">National Geographic</a></em>. "They have their own antiquity to their tool use." </p>
Intense lightning could have burned us out of the trees.
- A new paper proposes that a couple of supernovae led to the loss of our tree habit, forcing us down to the savannah.
- The telltale clues are iron-60 isotopes and lots of unexplained charcoal and soot in the geologic record.
- The theory is an intriguing combination of astronomy, physics, geology, and anthropology.
The clues<p><u></u>In 2016, Melott authored a <a href="https://news.ku.edu/2016/04/01/proof-ancient-supernovae-zapped-earth-sparks-hunt-aftereffects" target="_blank">paper</a> that documented the incongruous presence of iron-60 isotopes in ancient seabed deposits and postulated that they came from supernovae about 325 light years distant. That same year, research from a team led by astrophysicist <a href="https://www-astro.physik.tu-berlin.de/~breitschwerdt/" target="_blank">Dieter Breitschwerdt</a> got more specific: It was precisely two such events, one supernova 1.7 to 3.2 million years back, and the other one 6.5 to 8.7 million years ago.</p><p>At the time, Melott <a href="https://news.ku.edu/2016/04/01/proof-ancient-supernovae-zapped-earth-sparks-hunt-aftereffects" target="_blank">noted</a>, "Our local research group is working on figuring out what the effects were likely to have been. We really don't know. The events weren't close enough to cause a big mass extinction or severe effects, but not so far away that we can ignore them either. We're trying to decide if we should expect to have seen any effects on the ground on the Earth." </p><p>Then there's the unexplained high levels of charcoal and soot that appear in the geologic layer a few million years back. Melott asserts that this may indicate an unusual amount of global forest-burning. "It's all over the place," says Melott, "and nobody has any explanation for why it would have happened all over the world in different climate zones."</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTU2MzE0OC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1NzAzNDIyMH0.W6XTDa5xYok4rl1ExvmqwVsLjiPLlnksv30bUPT6kXI/img.jpg?width=980" id="0fdf2" class="rm-shortcode" data-rm-shortcode-id="e430672230f69ecda96790719ed9f544" data-rm-shortcode-name="rebelmouse-image" />
Image source: Andrey Andreyev/Unsplash
2 + 2<p>Putting these two mysteries together, Melott explains how the supernovae could have led to humanity's arboreal habitat being reduced to cinders.</p><p>"We calculated the ionization of the atmosphere from cosmic rays which would come from a supernova about as far away as the iron-60 deposits indicate," says Melott. The more recent of the two appears to have hit the Earth harder. "We contend it would increase the ionization of the lower atmosphere by 50-fold. Usually, you don't get lower-atmosphere ionization because cosmic rays don't penetrate that far, but the more energetic ones from supernovae come right down to the surface — so there would be a lot of electrons being knocked out of the atmosphere."</p><p>This would affect the bottom mile of our atmosphere in an exceptional way: "When high-energy cosmic rays hit atoms and molecules in the atmosphere, they knock electrons out of them — so these electrons are running around loose instead of bound to atoms." Melott says that this abundance of available electrons would have made it far easier for lightning bolts to form, increasing the likelihood of forest fires. The timing's about right geologically.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTU2NTIwMC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzMzA4NzE0OX0.Z6N-wxOuPJqKplM0yEWsr2_7eVywwR5JuY9-FXwgrHQ/img.jpg?width=1245&coordinates=64%2C35%2C64%2C35&height=700" id="e7893" class="rm-shortcode" data-rm-shortcode-id="2b65fdbb196bc3225518bb8c0b39b79c" data-rm-shortcode-name="rebelmouse-image" />
Image source: Infinitum Produx/Shutterstock
What about us?<p>Though some of our ancestors are thought to have begun <em>experimenting</em> with walking upright prior to the time at which the lightning would have occurred, they were still primarily living among the trees.</p><p>However, says Melott, the "increase in fires is thought to have stimulated the transition from woodland to savanna in a lot of places — where you had forests, now you had mostly open grassland with shrubby things here and there." </p><p>He adds that this new theory fits with northeast African human evolution,"Specifically, in the Great Rift Valley where you get all these hominin fossils."</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTU2NTIwMi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxMzUxMDE5NH0.g1cCxLjFRzgbgP_R5Cg0Sh3Qd5TYhpl5d0nNoZ3W5Xo/img.jpg?width=1245&coordinates=401%2C397%2C401%2C397&height=700" id="212d2" class="rm-shortcode" data-rm-shortcode-id="c290e689af571dc15dfc1ced778adc8d" data-rm-shortcode-name="rebelmouse-image" />
Image source: Sho Hatakeyama/Unsplash