Tree of Life Poster

Tree or Web? Today, the Tree of Life looks more like a Web of Life than a tree. This web-like appearance is due to DNA that moves between species. This "horizontal gene transfer" is indicated by white lines. Horizontal gene transfer is a powerful force in evolution. Generous Genes Originally, people thought DNA was only passed from parent to child. Then, scientists observed that DNA could be transfered horizontally from cousin to cousin and species to species within the bacteria and archaea. DNA that moves around is generous, giving new abilities to recipient organisms. Now, more and more scientists are finding examples of generous genes that transfer horizontally between plants, animals and fungi! Horizontal Gene Transfer is such an important mechanism for evolution that the eukaryotes have evolved ways to move DNA. Come Together The biggest leaps forward in evolution occurred when two different species merged to form an entirely new creature. This merger is called endosymbiosis. Famous examples of endosymbiosis are mitochondria and chloroplasts. Deep Time and the Origin of Life Most scientific images of the Tree of Life go back only around 500 million years ago. This image shows life from the beginning, about 3.7 billion years ago. At this scale, humans (magenta line-dot near top) appeared less than 5 pixels from the top of the tree! Although more and more is known about how organisms evolved, the origin of life remains a mystery. The white lines at the base of the tree indicate the origins of life. Our Last Universal Common Ancestor, LUCA, may have been a community of organisms. Science This Trees of Life, also known as a “phylogenetic tree,” is based on DNA sequence similarities that show how all creatures are related evolutionarily. Colorful pictures at top of this tree represent the diversity of creatures alive today. Numbers along the left side indicate the billions of years before the present. Although relatively simple and colorful, this Tree of Life image is based on data from hundreds of researchers using the tools of molecular biology. This image is based on comparisons of DNA sequences from thousands of organisms.