Tag: human evolution

Categories : Injury & TraumaTags :

Exposure to Burn Injuries may have Played Key role in Shaping Human Evolution

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Photo by sena keçicioğlu

Humans’ exposure to high temperature burn injuries may have played an important role in our evolutionary development, shaping how our bodies heal, fight infection, and sometimes fail under extreme injury, according to new research.

For more than one million years, the control of fire has powered human success, from cooking and heating to technology and industry, driving genetic and cultural evolution and setting us apart from all other species. But this relationship has also exposed humans to high temperature injuries at a scale unmatched in the natural world. 

Humans burn themselves – and survive burns – with a frequency likely much greater than any other animal. Most animals avoid fire completely, while in contrast, humans live alongside fire and most humans will experience minor burns throughout their lives. 

A new study published in BioEssays, led by Imperial College London researchers, suggests that this increased exposure to burn injuries may have driven notable genetic adaptations which differentiated humans from other primates and mammals. This may also explain both beneficial and maladaptive responses to severe burn injury. 

Burn injuries exist on a spectrum of severity, with most small injuries healing on their own while severe burns can lead to lifelong disability or death. Burns damage the skin, the body’s main protective barrier against infection, sometimes over large areas of the body. The longer the skin is damaged, the greater the risk that bacteria can enter the body and cause overwhelming infection. 

The researchers argue that natural selection would have favoured traits that helped humans survive small to moderate burns. These may include faster inflammation, faster wound closure (to prevent infection) and stronger pain signals. 

However, while these traits are helpful for less severe injuries, they can become harmful for large burns, which may explain why modern humans can experience extreme inflammation, scarring, and organ failure from major burns. 

Using comparative genomic data across primates, the researchers found examples of genes associated with burn injury responses which show signs of accelerated evolution in humans. These genes are involved in wound closure, inflammation and immune system response – likely helping to rapidly close wounds and fight infection; a major complication after burn injury, particularly before the widespread use of antibiotics. 

These findings support the theory that exposure to burn injuries may have been a notable force on the evolution of humans. 

Dr Joshua Cuddihy, lead author for the study, and Honorary Clinical Lecturer in Imperial’s Department of Surgery and Cancer, said: “Burns are a uniquely human injury. No other species lives alongside high temperatures and the regular risk of burning in the way humans do.  

“The control of fire is deeply embedded in human life — from a preference for hot food and boiled liquids to the technologies that shape the modern world. As a result, unlike any other species, most humans will burn themselves repeatedly over their lifetime, a pattern that likely extends back over a million years to our earliest use of fire.

“Our research suggests that natural selection favoured traits that improved survival after smaller, more frequent burn injuries. However, those same adaptations may have come with evolutionary trade-offs, helping to explain why humans remain particularly vulnerable to the complications of severe burns.”

The control of fire has powered human success for more than one million years

The research was developed through a collaboration between burn injury experts, evolutionary biologists, and genetics experts at Imperial, Chelsea and Westminster Hospital NHS Foundation Trust, and Queen Mary University of London.

The study’s novel perspective on human evolution, which could reshape our understanding of modern burn care and human biology, was made possible through interdisciplinary collaboration between clinicians and researchers. 

Professor Armand Leroi, Professor of Evolutionary Developmental Biology in Imperial’s Department of Life Sciences, said: “What makes this theory of burn selection so exciting to an evolutionary biologist is that it presents a new form of natural selection – one, moreover, that depends on culture. It is part of the story of what makes us human, and a part that we really did not have any inkling of before.”

Yuemin Li, PhD student at Queen Mary University of London, said: “Our study provides compelling evidence that humans have unique adaptive mutations in several key genes associated with burn injury response. 

“These findings could allow us to explore in future research how genetic variations in different groups impact burn injury response, potentially explaining why some patients heal well or poorly after a burn.” 

Unlike other wounds from cuts or bites which would have also led to infections, the increased lifetime risk of burns experienced by humans and their hominin ancestors is unique as they are the only species to regularly experience burn injuries and survive them. 

The researchers’ findings could change how we study burn injuries, design treatments, and interpret complications of burns. It may also explain why translating results on burn injuries from animal models to humans is often ineffective. 

Declan Collins, Consultant in Plastic and Reconstructive Surgery at Chelsea and Westminster Hospital NHS Foundation Trust, said: “Understanding the evolutionary drivers that cause genetic change is an important step in burn research that will influence the way in which we look at scar formation and wound healing. 

“The genetic basis for scarring variation in humans and response to tissue injury is still poorly understood, and this work will provide new angles for future research.” 

‘Burn Selection: How Fire Injury Shaped Human Evolution’ by Joshua Cuddihy et al. is published in Bioessays.

By Conrad Duncan

Source: Imperial College London

Categories : NeurologyTags :

Microbes May Hold the Key to the Brain’s Evolution

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First-of-its-kind study offers evidence that microbes from different primate species influence physiology in ways linked to brain size and function

Source: Pixabay

Humans have the largest relative brain size of any primate, but little is known about how mammals with larger brains evolved to meet the intense energy demands required to support brain growth and maintenance.

A new study from Northwestern University provides the first empirical data showing the direct role the gut microbiome plays in shaping differences in the way the brain functions across different primate species.

“Our study shows that microbes are acting on traits that are relevant to our understanding of evolution, and particularly the evolution of human brains,” said Katie Amato, associate professor of biological anthropology and principal investigator of the study, which was published in PNAS. 

The study builds upon previous findings from Amato’s lab that showed the microbes of larger-brained primates, when introduced in host mice,  produced more metabolic energy in the microbiome of the host – a prerequisite for larger brains, which are energetically costly to develop and function. This time, the researchers wanted to look at the brain itself to see if the microbes from different primates with different relative brain sizes would change how the brains of host mice functioned. 

What they found

In a controlled lab experiment, the researchers implanted gut microbes from two large-brain primate species (human and squirrel monkey) and one small-brain primate species (macaque) into microbe-free mice.  

Within eight weeks of making changes to the hosts’ microbiomes, they observed that the brains of mice with microbes from small-brain primates were indeed working differently than the brains of mice with microbes from large-brain primates. 

In the mice with large-brain primate microbes, the researchers found increased expression of genes associated with energy production and synaptic plasticity, the physical process of learning in the brain. In the mice with smaller-brain primate microbes, there was less expression of these processes. 

“What was super interesting is we were able to compare data we had from the brains of the host mice with data from actual macaque and human brains, and to our surprise, many of the patterns we saw in brain gene expression of the mice were the same patterns seen in the actual primates themselves,” Amato said. “In other words, we were able to make the brains of mice look like the brains of the actual primates the microbes came from.”

Another surprising discovery the researchers made was a pattern of gene expression associated with ADHD, schizophrenia, bipolar and autism in the genes of the mice with the microbes from smaller-brained primates. 

While there is existing evidence showing correlations between conditions like autism and the composition of the gut microbiome, there is a lack of data showing the gut microbes contribute to these conditions. 

“This study provides more evidence that microbes may causally contribute to these disorders —specifically, the gut microbiome is shaping brain function during development,” Amato said. “Based on our findings, we can speculate that if the human brain is exposed to the actions of the ‘wrong’ microbes, its development will change, and we will see symptoms of these disorders, i.e., if you don’t get exposed to the ‘right’ human microbes in early life, your brain will work differently, and this may lead to symptoms of these conditions.” 

Implications and next steps

Amato sees clinical implications for further exploration of the origins of some psychological disorders and for taking an evolutionary perspective on the way microbes affect brain physiology.

“It’s interesting to think about brain development in species and individuals and investigating whether we can look at cross-sectional, cross-species differences in patterns and discover rules for the way microbes are interacting with the brain, and whether the rules can be translated into development as well.

“Primate gut microbiota induce evolutionarily salient changes in mouse neurodevelopment” was published by the Proceedings of the National Academy of Sciences on Jan. 5.

Source: Northwestern University

Categories : Neurology Skeletal SystemTags :

A Single Gene Variant that Gave Rise to Humans’ Unique Skull Base

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Source: CC0

One of the unique features that Homo sapiens have compared with other closely related hominin species and primates is the shape of the base of the skull, which enabled larger brains to evolve. Now, in a study recently published in the American Journal of Human Genetics, a team from Tokyo Medical and Dental University (TMDU), the University of Helsinki, and the University of Barcelona has analysed a genomic variant responsible for this unique human skull base morphology.

Most of the genomic changes that occurred during human evolution did not occur directly to genes themselves, but in regions responsible for controlling and regulating the expression of genes. Variants in these same regions are often involved in genetic conditions, causing aberrant gene expression throughout development. Identifying and characterising such genomic changes is therefore crucial for understanding human development and disease.

The development of the basicranial region, the base of the skull where it joins the vertebra, was key in the evolution of Homo sapiens, as we developed a highly flexed skull base that allowed our increased brain size. Therefore, variants that affect the development of this region are likely to have been highly significant in our evolution.

First, the team searched for variants in just a single letter of the DNA code, called single nucleotide polymorphisms (SNPs), that caused different regulation of genes in the basicranial region in Homo sapiens compared with other extinct hominins. One of these SNPs stood out, located in a gene called TBX1.

They then used cell lines to show that the SNP, called “rs41298798,” is located in a region that regulates the expression levels of the TBX1 gene, and that the “ancestral” form of the SNP, found in extinct hominins, is associated with lower TBX1 expression, while the form found in Homo sapiens gives us higher levels of TBX1.

“We then employed a mouse model with lower TBX1 expression,” explains lead author Noriko Funato, “which resulted in distinct alterations to the morphology at the base of the skull and premature hardening of a cartilage joint where the bones fuse together, restricting the growth ability of the skull.” The changes in the Tbx1-knockout mice were reminiscent of the known basicranial morphology of Neanderthals.

These morphological changes are also reflected in human genetic conditions associated with lower TBX1 gene dosage, such as DiGeorge syndrome and velocardiofacial syndrome, further indicating the significance of this genetic variant in the evolution of our unique skull base morphology.

The identification of this genomic variant sheds light on human evolution, as well as providing insight into common genetic conditions associated with lower expression of the TBX1 gene, paving the way for greater understanding and management of these conditions.

Source: Tokyo Medical and Dental University