Tag Archives: homo

Running man.

One broken gene made us very good runners

A genetic fluke two to three million years ago turned humans into the best endurance runners around.

Running man.

Image via Pixabay.

A new paper published by researchers from the University of California San Diego School of Medicine reports that our ancestors’ functional loss of one gene called CMAH dramatically shifted our species’ evolutionary path. The loss altered significant metabolic processes, with impacts on fertility rates and risk of developing cancer.

The same change may have also made humans one of the best long-distance runners on Earth, the team adds.

These genes were made for runnin’

Our ancestors were presumably quite busy two to three million years ago transitioning from living in trees to live on the savannah. They were able to walk upright by this time, but they weren’t particularly good at it.

However, soon after this, some of our ancestors’ physiology starts undergoing some striking changes. Most relevant are shifts we see in their skeletons, resulting in long legs, big feet, and large gluteal muscles (butts) — all very good for walking around. These shifts were also accompanied by the evolution of sweat glands with much the same layout and capacity as ours which, according to the team, is quite expansive and much better at dissipating heat than that of other large mammals.

In other words, humanity received powerful legs and one of the most solid cooling systems in one fell swoop.

Our ancestors proceeded to use their new toys to hunt and eat anything they could bring down. They did so by adopting a hunting pattern unique among primates (and very rare among animals in general) known as persistence hunting: they would go out in the heat of the day, when other carnivores were resting, relying on their legs and sweat glands to chase prey until — exhausted and overheated — it couldn’t physically run away anymore.

We didn’t know much about the biological changes that underpinned this radical change, however. The first clues were uncovered around 20 years ago — when Ajit Varki, a physician-scientist at the University of California, San Diego (UCSD), and colleagues unearthed one of the first genetic differences between humans and chimps: a gene called CMP-Neu5Ac Hydroxylase (CMAH). Other species of primates also have this gene.

We, however, have a broken version of CMAH. Varki’s team calculated that this genetic change happened 2 million to 3 million years ago, based on the genetic differences among primates and other animals.

More recent research has shown that mice models with a muscular dystrophy-like syndrome exhibit more acute symptoms when this gene is inactivated. This hinted to Varki that the faulty gene might be what led to the changes our ancestors experienced in the savannahs.

“Since the mice were also more prone to muscle dystrophy, I had a hunch that there was a connection to the increased long distance running and endurance of Homo,” said Varki.

UCSD graduate student Jonathan Okerblom, the study’s first author, put the theory to the test. He built mouse running wheels, borrowed a mouse treadmill, and pitted mice with a normal and broken version of CMAH to the task.

“We evaluated the exercise capacity (of mice lacking the CMAH gene), and noted an increased performance during treadmill testing and after 15 days of voluntary wheel running,” Okerblom explained.

The two then consulted Ellen Breen, Ph.D., a research scientist in the division of physiology, part of the Department of Medicine in the UC San Diego School of Medicine. She examined the mice’s leg muscles before and after running different distances, some after 2 weeks and some after 1 month.

After training, mice with the human-like version of CMAH ran 12% faster and 20% longer than the other mice, the team reports. Breen adds that the mice displayed greater resistance to fatigue, increased mitochondrial respiration and hind-limb muscle, with more capillaries to increase blood and oxygen supply. Taken together, Varki says the data suggest CMAH loss contributed to improved skeletal muscle capacity for oxygen utilization.

“And if the findings translate to humans, they may have provided early hominids with a selective advantage in their move from trees to becoming permanent hunter-gatherers on the open range.”

The most likely cause of this change was evolutionary pressures associated with an ancient pathogen, the team explains.

The version of the gene we carry determines the loss of a sialic acid called N-glycolylneuraminic acid (Neu5Gc), and accumulation of its precursor, called N-acetylneuraminic acid or Neu5Ac, which differs by only a single oxygen atom. Sialic acids serve as vital contact points for cell-to-cell interaction and cellular interactions with the surrounding environment. This change likely led to enhanced innate immunity in early hominids, according to past research.

Sialic acids may also be a biomarker for cancer risk, and the team has also reported that certain sialic acids are associated with increased risk of type 2 diabetes; may contribute to elevated cancer risk associated with red meat consumption, and trigger inflammation.

“They are a double-edged sword,” said Varki. “The consequence of a single lost gene and a small molecular change that appears to have profoundly altered human biology and abilities going back to our origins.”

The paper “Human-like Cmah inactivation in mice increases running endurance and decreases muscle fatigability: implications for human evolution” has been published in the journal Proceedings of the Royal Society B.

Sapiens-Neanderthal.

Man-made: we’ve domesticated our own species

They don’t make humans like they used to — quite literally. Living in social groups has led us to self-domesticate our species, new research finds.

Sapiens-Neanderthal.

Image credits hairymuseummatt / Wikimedia.

According to the hypothesis of human self-domestication, one of the forces that powered and steered our evolution was artificial selection in the cave, tribe, or hut. As we like to live with other people (and there’s no indication that this was ever different), prosocial behavior became valuable while antisocial behavior became increasingly shunned throughout our history — which created a selective evolutionary pressure for the former. New research, led by Professor Cedric Boeckx from the University of Barcelona, comes to offer genetic evidence in favor of this hypothesis.

The goodest boy is you!

Self-domestication is, in broad strokes, pretty much like regular domestication. Outwardly, it leads to a change in anatomical features — for example, imagine how dogs have adorable droopy ears and rounder heads while wolves have scary pointed ears and more angular heads. It also leads to behavioral changes, most notably a reduction in aggressiveness. The key difference, however, is that self-domestication of a species is done internally, if you will, without input from other species.

It’s a process that several researchers believe helped shaped modern humans, as well as other species, such as bonobos. Up to now, however, we lacked any genetic evidence to help prop this hypothesis up. Boeckx’s team worked with the genomes of our extinct (and wild) Neanderthal or Denisovan relatives to try and determine whether humans have, in fact, domesticated themselves.

They compared the genetic material from modern humans against that of several domesticated species and their wild type. The comparison aimed to find overlapping genes associated with domestication, such as those linked to docile behavior or gracile facial features. The researchers first compiled a list of domestication-associated genes in humans based on the comparison with Neanderthals and Denisovans, wild but extinct human species. Then, they compared this list to genomes from domesticated animals and their wild type.

According to their paper, there are a “statistically significant” number of domestication-associated genes which overlapped between modern humans and domestic animals, but not with their wild types. The team says these results strengthen the self-domestication hypothesis and help “shed light on […] our social instinct.”

“One reason that made scientists claim that humans are self-domesticated lied within our behavior: modern humans are docile and tolerant, like domesticated species, our cooperative abilities and pro-social behaviour are key features of our modern cognition,” says Boeckx.

“The second reason is that modern humans, when compared to Neanderthals, present a more gracile phenotype that resembles the one seen in domesticates when compared to their wild-type cousins,” added the expert.

[accordion style=”info”][accordion_item title=”What’s a phenotype?”]The phenotype represents an organism’s characteristics resulting from the interaction between its genes (genotype) and the environment. While the genotype dictates characteristics such as, let’s say, eye color, skin color, or maximum height, your phenotype is your actual height (a product of nutrition and genetics), your actual skin color (a product of exposure to sunlight and genetics), so on.

As a rule of thumb, the genotype is the digital blueprint and the phenotype is what actually came out on the production line.

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The team used other statistical measures, including control species, to make sure they weren’t picking up on a fluke. Their aim was to rule out the possibility that these genes would randomly overlap between humans and domesticated animals, so they compared the genomes with species of great apes.

“We found that chimpanzees, orangutans and gorillas do not show a significant overlap of genes under positive selection with domesticates. Therefore, it seems there is a ‘special’ intersection between humans and domesticated species, and we take this to be evidence for self-domestication,” Boeckx said.

There’s still a lot of work left if we’re to tease out the physical, mental, and behavioral characteristics that these genes impart onto us. However, some broad lines can already be drawn, the team believes: Boeckx himself suspects that self-domestication might explain why humans are so ridiculously cooperative or our “special mode of cognition”,

The paper “Self-domestication in Homo sapiens: Insights from comparative genomics” has been published in the journal PLOS One.

Shadows.

Humans got taller, then bulkier in ‘bursts’ during our evolution

Hominins have seen “pulses” of growth during their evolutionary history, followed by periods of “stagnation,” a new paper reports. This was the widest-scale study on the evolution of human stature and weight to date. Data was drawn from hominid fossils spanning the entire known evolutionary path of the genus. It reveals that over the last four million years, hominid stature and body mass have increased independently and at different speeds. Some extinct lineages even went through phases of shrinking.

Shadows.

Image credits Igor Ovsyannykov.

The paper drew on 311 specimens dating from roughly 4.4 million years ago (the time of the earliest known upright hominid species) through to the modern humans that followed the last ice age. It’s the largest study of hominid body size evolution to date, and the authors conclude that although this was a “long and winding road with many branches and dead ends,” the overarching pattern they’ve observed is one of bursts of growth followed by millennia of ‘stagnation’.

Taller, bigger, better

Earlier hominin evolution saw a wide range of body sizes, mostly owed to the number of different species and their particular evolutionary roots. Some were broad, ‘gorilla’-like, such as Paranthropus, or slimmer and agiler, as was Australopithecus afarensis. On average, hominins from four million years ago weighed a roughly 25kg and stood at 125-130cm tall. Observing how physicality evolved over time, however, the team reports at least three major “pulses” of significant changes.

The first one occurred as our own genus, Homo, made an appearance around 2.2-1.9 million years ago. This period saw an increase in both height (of about 20 cm) and weight (of between 15-20 kg).

Stature and height further separated about 1.4 to 1.6 million years ago, following the emergence of Homo erectus. Fossil evidence shows that hominid species living around this time grew taller by roughly 10 centimeters (3.93 inches) but wouldn’t significantly gain in body mass for another million years. This is the point where a familiar stature was reached. Body mass still remained lower on average than today.

It would take roughly one million years (around 0.5 to 0.4 million years ago) before heavier hominids made a consistent appearance in the fossil record. On average, hominid species saw a body mass increase of 10-15 kgs (22-33 pounds) about 500,000 years ago. This increase in body mass likely points to an adaptation to environments north of the Mediterranean.

Height and stature chart.

A and b show weight (kg, blue) and stature (cm, green) evolution over time, by geologic period and taxa, respectively. C and d show variations (in %) for weight and stature, by geologic period and taxa, respectively.
Image credits Manuel Will, Adrián Pablos, Jay T. Stock, 2017, RSOS.

“From then onwards, average body height and weight stays more or less the same in the hominin lineage, leading ultimately to ourselves,” says lead author Dr Manuel Will from Cambridge’s Department of Archaeology, and a Research Fellow at Gonville and Caius College.

There are a couple of exceptions, as is the case for Homo naledi and Homo floresiensis, which have in fact decreased in size over time, the team reports. However, this was likely due to their evolutionary roots in smaller-bodied ancestors, or the effect of evolutionary pressures acting on isolated and small populations. Floresiensis, for example, was discovered on an Indonesian island.

“Our study shows that, other than these two species, hominins that appear after 1.4m years ago are all larger than 140cm and 40kg. This doesn’t change until human bodies diversify again in just the last few thousand years.”

“These findings suggest extremely strong selective pressures against small body sizes which shifted the evolutionary spectrum towards the larger bodies we have today.”

Sizing up to the requirements

This tall to ride.

Image via NewStorkCity.

The findings could help us better understand what early hominids were up to. Initially, hominid height and weight largely evolved “in concert,” the team adds. The latter decoupling between height and bulk were likely caused by early humans’ migration out of the forest and as an adaptation to hunting in the savannah.

“An increase solely in stature would have created a leaner physique, with long legs and narrow hips and shoulders. This may have been an adaptation to new environments and endurance hunting, as early Homo species left the forests and moved on to more arid African savannahs.” Dr Will adds.

“The higher surface-to-volume ratio of a tall, slender body would be an advantage when stalking animals for hours in the dry heat, as a larger skin area increases the capacity for the evaporation of sweat.”

Later, as these populations moved further north and ran into colder climates, the increase in bulk would make them better at fighting the cold.

“The later addition of body mass coincides with ever-increasing migrations into higher latitudes, where a bulkier body would be better suited for thermoregulation in colder Eurasian climates.”

The results also suggest cladogenesis (lineage-splitting) may have played a part in increasing the average human’s height and mass. It’s possible that inter-species competition later drove the smaller-bodied lineage extinct. Sexual dimorphism — the physical distinction between genders, with mammalian females typically smaller than males — was also more prevalent in early hominid history, the authors added, and seems have become less emphasized.

However, Will says the theory should be taken with a grain of salt. It suits the available data very well, but there are vast gaps in the fossil record that the team has had to work around, ones that may have obscured the truth. He notes that at times, the team had to work on body size estimates starting from very fragmented remains, in some cases from as little as a single toe bone.

Overall, we know certain groups of humans have continued getting taller over the last century, most likely due to improvements in nutrition and healthcare. As these keep increasing, it’s likely that the average human stature is going to keep increasing.

“However, there is certainly a ceiling set by our genes, which define our maximum potential for growth,” said co-author Dr Jay Stock, also from Cambridge’s Department of Archaeology.

The paper “Long-term patterns of body mass and stature evolution within the hominin lineage” has been published in the journal Royal Society Open Science.

Neanderthal cave painting

Neanderthal and modern humans shared long childhoods

The rare discovery of a Neanderthal boy’s partial skeleton suggests he had similar growth patterns to those seen in modern humans. It’s yet another sign that the two species from the same Homo genus were very similar to one another.

Neanderthal cave painting

Credit: Wikimedia Commons.

The remains of the seven-year-old boy called El Sidron J1 are 49,000 years old. They were unearthed at the El Sidron archaeological site in Spain, a famous middle Paleolithic karst cave which has time and time again revealed insights into the lives of Neanderthals. Previously, bones retrieved from the site indicated Neanderthals engaged in cannibalism.

At the same cave, which stretches for approximately 3,700 meters (2.5 miles), with a central hall of approximately 200 m (650 feet), archaeologists have found over 400 lithic artifacts fashioned by Neanderthals. These include side scrapers, denticulates, hand axes, as well as several Levallois points, all made from local sources, mostly chert, silex, and quartzite.

More of the same

Spanish researchers working with the Paleoanthropology Group at Museo Nacional de Ciencias Naturales report the small Neanderthal boy was still evidently growing when he died. His brain was about 87.5% the size of that of an average adult Neanderthal. By the same age, a modern human boy should have a brain that’s 95% the size of an adult.

The boy’s vertebrae hadn’t yet fused, bone analysis showed. In modern human boys, the same bones typically fuse between age four to six. Limb bones, however, matured at the same rate as human boys, the authors reported in the journal Science. 

It might be possible that Neanderthal children enjoyed a longer childhood but it’s far too early to draw such a conclusion. We only have one such specimen, even that made of just 36% of his left side and parts of his skull.

The partial skeleton of a Neandertal boy he grew slowly, akin to modern human children. Credit: Paleoanthropology Group MNCNCSIC.

The partial skeleton of a Neandertal boy he grew slowly, akin to modern human children. Credit: Paleoanthropology Group MNCNCSIC.

Despite these dissimilarities, Neanderthal and modern human growth patterns are strikingly similar. In fact, it’s rather surprising that the differences are so subtle considering the two species didn’t evolve side by side. After splitting from a common ancestor during the Middle Pleistocene, Neanderthals evolved separately in western Eurasia while humans emerged from Africa.

The boy has been described by researchers as ‘sturdy’, having weighed 26 kilograms at his time of death and standing just over one meter (three and a half feet) tall. The cause of death is unknown though some cut marks on the bones could indicate cannibalism.

The findings cement a growing body of evidence that suggests Neanderthals and modern humans were strikingly similar. Neanderthals practiced rituals, made art, and buried their dead. Artifacts found in such places like El Sidron show that Neanderthals were at least as equally technologically proficient in stone tools as humans.

What’s more, they used manganese dioxide, today commonly found in batteries, to light fires some 50,000 years ago. Another recent study published just earlier this month showed that Neanderthals knew how to manufacture tar a good 200,000 years earlier than modern humans. And, lastly, the most important evidence of Neanderthal and Homo sapiens kinship can be found in almost every living, breathing human on the planet. Most Europeans and Asians have between 1 to 2 percent Neanderthal DNA, remnants from the time the two species interbred.

Neanderthals thrived in Europe from 240,000 to 30,000 years ago, until they abruptly disappeared. It’s thought that a combination of climate change and competition for food with humans wiped them off. Meanwhile, humans have not only risen to the top of the food chain — they’ve also mastered technology that can literally make us shoot for the moon. With this in mind, it’s tempting to consider ourselves as a superior master race. Personally, I can only reflect on a time when there were two Homo species sharing the same planet, until some fluke of fate destroyed one of them. We don’t know for sure what, but who’s to say it couldn’t have been the other way around? A world ruled by Neanderthals, and not us. Now, that would be an interesting place to visit.