How Virus-like 'Jumping Genes' Became Our Partners in Evolution Nearly half of the human genome is made up of transposable elements, also known as transposons or "jumping genes." These are genetic sequences that can move from one location in the DNA to another, either on the same chromosome or a different one. This movement can disrupt genes, expand the genome, and even spark new evolutionary traits. Barbara McClintock first identified these mobile elements in the 1940s while studying color variation in corn. Her work revealed that these elements could influence gene activity, and she was awarded the Nobel Prize in 1983 for her discovery. Transposons are generally divided into two main types: DNA transposons and retrotransposons. DNA transposons move using a "cut and paste" method, aided by enzymes called transposases. Retrotransposons, by contrast, copy themselves into RNA, which is then converted back into DNA and inserted into a new location. These elements are closely related to retroviruses, which also insert their genetic material into host DNA. Over time, retrotransposons can accumulate in the genome and make up a large portion of it in various species. Transposons can also move between species through a process called horizontal transfer, often aided by viruses. This phenomenon has been observed in many organisms, from fungi to vertebrates. In 2020, scientists found nearly 1,000 cases of horizontal transfer in the genomes of 307 vertebrates, with fish being the most common hosts. The role of transposons in evolution is becoming more widely recognized. For example, a transposon insertion in the cortex gene was linked to the change in wing coloration of peppered moths during the Industrial Revolution. This change occurred as environmental conditions favored darker moths, showing how transposons can quickly contribute to adaptive traits. Transposons can also be repurposed to form new genes or regulatory elements. They are connected to the evolution of animal eyes, the adaptive immune system in jawed vertebrates, and the placenta in mammals. The relationship between transposons and host genomes may be more of a coevolutionary partnership than a purely parasitic one. Some transposon-derived elements perform functions similar to native genes, and over time, the host genome may become reliant on them. The disruptive potential of transposons may have led to the evolution of epigenetic mechanisms to control their activity. These mechanisms, originally developed to suppress transposons, have been repurposed to regulate gene expression in general, contributing to the development of complex multicellular life. Scientists now view transposons not as "junk" DNA, but as integral components of the genome's regulatory system, playing a significant role in evolutionary innovation.