The Last Universal Common Ancestor (LUCA) in Evolution

Charles Darwin's theory of evolution proposed that all life on Earth originated from a common ancestor. In "Origin of Species," Darwin suggested, "Therefore I should infer from analogy that all the organic beings which have ever lived on this earth have descended from the same one primordial form, into which life was first breathed." LUCA, or the Last Universal Common Ancestor, also known as the Last Common Ancestor (LCA), isn't necessarily the first life form but is the most recent ancestor from which all current life forms evolved around 3.9 billion years ago, sharing its genetic traits.

Living organisms are categorized into three main branches: eukaryotes (including plants, animals, protozoa, and those with nuclei), and bacteria and archaea (two branches lacking nuclei). Identifying characteristics that define LUCA has proven challenging and contentious. Initially considered a simple, primitive entity, LUCA is now understood to be more complex.

In 2010, a formal test was proposed to assess common features expected in a LUCA candidate. LUCA was likely a single-celled organism enclosed by a lipid membrane. Other characteristics relate to genetics, biochemistry, energy sources, and reproduction. All living beings encode genetic information in DNA, and the genetic code translating DNA into enzymes and proteins is nearly identical from bacteria to humans. This genetic commonality supports the concept of LUCA, making it less likely that life originated from multiple ancestors.

One significant challenge in identifying LUCA lies in gene swapping, where genes can transfer between organisms, making it difficult to ascertain whether observed characteristics are universal or the result of genetic exchange.

The Tree of Life, symbolizing our shared origin, serves as a metaphor across various global theologies and mythologies. This depiction of the Tree of Life, dating back to around 1797 and originating from the Palace of the Shaki Khans, is currently exhibited at the Azerbaijan National Art Museum.