How the Naked Ape Became the Fat Ape: Evolution, Diet, and Modern Challenges

Overview

Humans have always carried more body fat than other primates like chimpanzees. This isn’t just because of our lifestyles or diet choices. Although junk foods and a sedentary lifestyle play a part, the real difference lies deeper, beyond our DNA sequences, and into how our genes are expressed. Scientists at Duke University discovered that specific changes in fat cells happened historically due to epigenetic factors. This means that even though humans and chimps have nearly identical DNA, our fat cells behave differently.

These researchers found that in humans, certain genes that could turn white fat into beige or brown fat are often inaccessible due to how our DNA is packed within fat cells. This bunching restricts these genes, which makes humans store more fat. Healthy human adults typically have 14-31% body fat, while other primates usually have less than 9%.

Key Differences in Fat Cells

Scientists used a technique called ATAC-seq to analyze the genomes of humans, chimpanzees, and rhesus macaques. They discovered around 780 DNA regions more accessible in chimps and macaques but more bunched up in humans. These areas often include genes that can turn fat into a calorie-burning type, indicated by their epigenetic closure in humans.

Factor Humans Chimpanzees & Macaques
DNA Regions Less accessible More accessible
Body Fat % 14-31% Less than 9%
Calorie-Storing Fat Higher Lower

Implications of Epigenetic Changes

In human fat cells, DNA bunching happens in areas involving lipid metabolism and the transformation of fat cells into brown or beige fat, which burns calories rather than storing them. Because these areas are frequently inaccessible, humans maintain larger fat reserves than their primate relatives.

Dr. Gregory A. Wray from Duke University led this research team. Findings published in Genome Biology and Evolution pointed out that a crucial source of these differences in body fat was chromatin accessibility in cis-regulatory regions. These differences are significant for understanding many traits, including how body fat accumulates.

Fat Transformation

Devjanee Swain-Lenz, the first author of the study, noted that humans seem to lack some ability to convert white fat to the more beneficial brown or beige fat. This process isn’t entirely lost, but it requires effort, like exposure to cold temperatures, to activate the body’s limited brown fat reserves.

  • “We need to work for it,” she mentioned, emphasizing the complex nature of this biological process.

Fat cells play essential roles beyond just storing energy. They protect vital organs, insulate the body from cold, and help buffer against starvation. But humans may have evolved to store more fat as a survival strategy to meet the growing energy demands of our expanding brains.

Brain Growth and Energy Needs

Over millions of years, human brains have grown significantly larger compared to those of chimpanzees. This growth requires a substantial amount of energy. The shift toward more white fat storage might have given early humans the advantage of having extra energy reserves to nourish their larger brains.

Future Research Directions

Current research aims to figure out how to encourage the conversion of white fat to brown or beige fat. Brown fat has the potential to burn calories efficiently, which could help in combating obesity. Scientists believe that understanding the genetic differences observed among primates could eventually lead to new treatments. But this is still a distant goal.

  • Swain-Lenz pointed out that it’s not as simple as flipping a genetic switch to make people thin. If it were, the solution would already be in place.

The quest continues to uncover genes that control fat storage and burning, aiming for better obesity treatments. But, as Swain-Lenz highlighted, much more research is needed before these findings can be applied practically.

Highlights of the Study

  • Relative Chubbiness: Healthy humans have significantly higher body fat percentages compared to other primates.
  • Epigenetic Packaging: The key to understanding human fat lies in how genes are packaged rather than the DNA sequences themselves.
  • DNA Accessibility: Human DNA bunches up, making specific fat-burning genes inaccessible.
  • Fat Conversion: Humans have reduced capability to convert white fat into calorie-burning brown fat.
  • Brain Energy: The larger human brain demands more energy, contributing to our higher fat reserves.
  • Ongoing Research: Scientists are exploring potential gene therapies to improve fat conversion, but practical applications are still far off.

This groundbreaking research from Duke University sheds light on why humans are naturally more prone to storing fat compared to other primates. By diving into our chromatin landscapes and understanding these genetic nuances, scientists hope to find future solutions to manage obesity and improve metabolic health.

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