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Why Humans Don't Have Tails: Scientists Discover Gene Change
February 28th, 2024
Approximately 20 to 25 million years ago, an evolutionary split between apes and monkeys led to a significant physical change in our ancestral lineage: the loss of tails. For a long time, the scientific community has pondered the reasons and mechanisms driving this change. A recent discovery, now published in Nature, offers insights into the genetic underpinnings of this transition. Geneticist Bo Xia and a team employed genomic analysis along with CRISPR—a sophisticated gene-editing tool—to reveal that a single mutation within a critical gene is at least partially responsible for the loss of tails in apes and, by extension, humans.
The researchers carefully analyzed and compared the genetic sequences of six ape species, including humans, with those of 15 monkey species that have tails. After pinpointing a notable mutation, the scientists sought to validate their findings. They edited the gene in mice, resulting in mice that were born tailless, thus supporting their hypothesis.
However, Xia acknowledges that this discovery might just be one piece of a larger genetic puzzle responsible for the evolutionary change. Conversely, the driving force behind the disappearance of tails in our evolutionary ancestors remains a subject of debate. While some suggest it could be a byproduct of random genetic drift, others argue that it may have conferred a significant survival advantage, possibly relating to the development of upright walking.
Notably, scientists such as Miriam Konkel and Rick Potts muse that the absence of tails might have been instrumental in the evolution of a vertical posture in some apes, a precursor to arboreal life and, eventually, terrestrial bipedalism. It's observed that contemporary arboreal apes like orangutans and gibbons, despite lacking tails, have adjusted their movement to accommodate their tailless state, differing from tail-utilizing monkeys in their locomotion.
Addressing this evolutionary landmark, biologist Itai Yanai considers the loss of tails to be a profound shift in human ancestry, yet fully understanding the rationale for this change is limited by our current knowledge and technology. Only time travel could provide a definitive answer. This research not only adds to our understanding of human evolution but also exemplifies the power of genetic tools in uncovering the mysteries of our past.
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💭 Discussion Questions
1
. What recent scientific discovery, discussed in the article, has shed light on the genetic reasons behind the loss of tails in apes and humans?2
. How did the team led by geneticist Bo Xia employ CRISPR technology in their research, and what were the results of their genetic experiment on mice?3
. What are some of the theories mentioned in the article concerning the advantages or reasons for the evolutionary loss of tails in our ancestors?📖 Vocabulary
🌐 Cultural context
The article discusses evolutionary biology, a scientific field interested in the development of species over time. It references CRISPR technology, a modern genetic engineering method used for editing genomes. The debate over the significance and mechanisms of evolution is part of a long-standing scientific discourse.
🧠 Further reading
Comparative genomics
Comparative genomics is a scientific discipline where researchers study and analyze the genomes, which consist of DNA sequence, gene structure, and other important genetic markers, of different species to uncover their biological and evolutionary interconnections. Fundamental to this field is the assumption that organisms sharing common characteristics also share conserved DNA coding for those traits. This method involves aligning genome sequences to look for common ancestral sequences, known as orthologous sequences, to determine the level of conservation and infer evolutionary links.
This field began in earnest with the sequencing of the genomes of certain bacteria in 1995. Ever since, comparative genomics has become an essential tool in genome sequence analysis, largely due to remarkable progress in DNA sequencings technology, especially during the late 2000s. Researchers now efficiently compare multiple genomes in one study, revealing significant genomic similarities not just between closely related species like humans and chimpanzees, but also between species that appear quite distinct phylogenetically, such as humans and yeast. The findings underline the intricate genetic divergences that take place across evolutionary paths.
Genetic algorithm
Genetic algorithms (GAs) represent a sophisticated computational method that draws inspiration from the principles of natural selection, a phenomenon observed in biological evolution. These algorithms fall under the broader category of evolutionary algorithms and are particularly effective for tackling complex optimization and search challenges. By leveraging natural processes such as mutation, crossover, and selection, GAs are adept at finding superior solutions across various applications. These may include refining decision trees to enhance their performance, cracking sudoku puzzles, optimizing model parameters, and exploring cause-and-effect relationships among variables.
To understand how genetic algorithms operate, imagine a population of potential solutions to a given problem. These solutions, which may be thought of as individual organisms, have unique characteristics encoded in their genetic makeup. Traditionally represented as strings of binary digits (0s and 1s), these characteristics can undergo changes through mutation and combination with others. The algorithm starts with a diverse population of these solutions, randomly generated, and embarks on an iterative journey of improvement. Within each cycle or generation, the algorithm assesses the "fitness" of each solution—typically, the objective function's value in the optimization problem.
The fittest solutions—those scoring highest on the fitness metric—are preferentially chosen to pass their genes to subsequent generations. Alterations to their genetic codes, mimicking biological recombination and mutation, generate a new set of potential solutions. Then, this updated group steps into the next phase of the algorithm. Typically, the genetic algorithm reaches its conclusion when it has either churned through a predetermined number of generations or achieved a desired level of solution fitness.
Implementing a genetic algorithm requires two key components: a suitable genetic encoding for the solutions within the domain of the problem and a robust fitness function capable of accurately assessing the quality of the solutions. These core requirements allow the algorithm to navigate the solution space effectively, gradually steering toward the most promising regions.
Human skeletal changes due to bipedalism
Humans initially evolved from primates, and this evolution has significantly altered the human skeletal structure, including pivotal changes to the configuration and dimensions of foot, hip, knee, leg bones, and the spine. These anatomical modifications have made walking on two legs rather than four a more energy-conserving activity. Numerous theories have emerged trying to explain this evolutionary step, often relating it to environmental transformations happening on Earth throughout history.
One of the most significant findings is that bipedal human walking is roughly 75% more energy-efficient than the walking of our closest living relatives, the chimpanzees, whether they are walking on all fours or on two legs. However, while walking conserves energy, human running does not offer the same benefit and is, in fact, less energy-efficient than walking. A study from 1980 indicated that bipedal walking is highly energy-efficient in hominins, the group to which humans belong, but when considering the energy costs of moving on all fours or on two legs, no difference was found.
In the evolution of human locomotion, the human foot has undergone significant changes. It has developed an enlarged heel to bear our body weight—a stark contrast to our primate ancestors who used their feet more like hands for grasping. Additionally, as humans evolved, the big toe realigned with the other toes and lost its ability to oppose them. For effective push-off during walking, human toes are slightly bent upwards. An arch in the human foot also evolved in contrast to the flat feet of non-human hominids, optimizing weight distribution from the heel, along the foot's outer edge, and across the arch towards the toes during each step.