Why Don’t Humans have Tails? Scientists Find Answers in an Unlikely Place

A common feature amongst most animals with backbones is a tail, something that humans lack. This has been mystery and questioned by many. In animals with tails, they are used for balance, propulsion, communication, and defense against biting insects. About 25 million years ago, primates said goodbye to the tails when they split from Old World monkeys. They no longer had a use for the tail. Our transition to bipedalism was thought to be connected to the loss of our tails, but we hadn’t known the genetics behind it. 

Now researchers have found new information that changes the trajectory of our thinking. They have found that our tail loss was due to a short sequence of genetic code that is abundant in our genome but was seen as junk DNA. Junk DNA is a sequence that serves no biological purpose for us. The identified snippet is an Alu element which is in the regulatory code of a gene associated with tail length called TBXT. Alu can switch their location in the genome which can trigger or undo mutations. At some point the Alu jumped into the TBXT gene in great apes and humans. Evolution is an interesting topic because it explains a lot of the world around us today. It was interesting to learn how we evolved to have no tail and how it no longer became any use to us. 

Main Article: https://www.cnn.com/2024/03/23/world/humans-tails-genetic-mutation-junk-dna-scn/index.html

2nd Link: https://www.nature.com/articles/s41586-024-07095-8 

A genetic parasite may explain why humans and other apes lack tails

The interesting theory that a genetic parasite, more specifically, an Alu element, might have been a major factor in apes' tail loss about 25 million years ago is looked at in this article. Scientists believe that this DNA element's insertion into the Tbxt gene, which is important for tail development, changed the gene's function and caused apes to lose their tails while monkeys kept them. This genetic modification presents questions about the evolutionary importance of ape tail loss and could offer insights into spinal cord disorders such as spina bifida. 

These findings show the complex interactions between evolution and genetics, showing how even small changes in genetic makeup can have a huge impact on morphology and development. Also, the study challenges earlier theories that transposons are just genetic "junk," showing their significance in creating basic biological structures and functions.

In my opinion, this shows the complicated evolutionary processes are and how important genetic factors are in determining morphological adaptations. It shows the complex genetic systems that cause major evolutionary shifts, opening up new research directions for studying the evolutionary background of other mammals with similar physical adaptations in addition to apes.

Sources:

https://www.sciencenews.org/article/genetic-parasite-humans-apes-tail-loss-evolution

https://www.cdc.gov/ncbddd/spinabifida/facts.html 

All Element May Be Why Humans and Other Apes Lack Tails

 A small piece of repetitive DNA called an Alu element may be what stole our tails. In the article by ScienceNews, they talk about the genetic change that may have caused humans and apes to lack a tail genetically. Alu elements are called “genetic parasites”, transposing, and jumping genes but they are not the parasites we know. The DNA gets inserted into the host’s DNA and can become permanent parts of the genetic code. Transposons are now believed to be a critical role in our evolution, and are possibly also linked to the placenta and immune system. 140 genes involving vertebrae tails development were analyzed and a piece of DNA on the tbxt gene differed between monkeys and apes. They tested this hypothesis in mice by genetically engineering shorter Tamils or none at all by altering the tbxt gene. Some mice even had spinal cord defects, also leading to a possible connection between spinal bifida. There are several other genes that may have Alu elements scattered throughout that have not been studied or discovered yet.

Imagine our daily lives if we still had tails like some of our ancestors. It wouldn’t be a much different world if we never lost that phenotypic trait and it was never not normal, but I am interested to see if they will do more research into the spinal cord abnormalities and the possibility that these elements can be the cause of these birth defects. Imagine how many other genes in our species as well as other species have been affected by these jumping genes…

Sources:

De Jesús, E. G. (2024, March 1). A genetic parasite may explain why humans and other apes lack tails. Science News. https://www.sciencenews.org/article/genetic-parasite-humans-apes-tail-loss-evolution

Deininger, P. L. (2011, January 1). Alu elements: know the SINEs. GenomeBiology.com (London. Print). https://doi.org/10.1186/gb-2011-12-12-236

Stem cell responsible for spinal regeneration located

Seeing a Gecko slowly regrow its tail may not seem that important to some people until it is pointed out what is inside the gecko's tail.  The article, "Cells driving gecko's ability to regrow its tail identified,"  goes into detail about the study done to examine the gecko's cell functions after the tail has been removed.  Inside the geckos tail, unlike in mammals, is a portion of the spinal cord so when the tail is removed the gecko is able to not only regrow the tail but the spinal cord as well.  The type of cell responsible is called "radial glia," which is a type of stem cell that is usually dormant.  However, once the injury is sustained the cells change function and begin to regenerate tissue rather than create scar tissue.  Discovering the cells responsible for this could mean the knowledge could be applied to human injuries by coaxing those cells to regenerate tissue rather than apply scar tissue.  As humans DNA code for the same type of stem cell as the geckos, for some reason it is not active in the regeneration process.  Putting scar tissue over the wound rather than regenerating tissue is a quick fix but is bad for the long run.  With this knowledge I think a better understanding of how the injuries can be solved preventing the lose of activity in some limbs due to the spinal injury, which would mean saving a lot of people the pain of having surgeries that may or may not work to regain control of their limbs.