R & D Summary

    The Face of LUCA (Last Universal Common Ancestor)

The concept of a Last Universal Common Ancestor (LUCA) is an inference from Charles Darwin's concept of evolution, where one species has to evolve from an ancestorial species. This suggest that the evolution of every known species on Earth today can be mapped out like a tree. However, what we see now are the tip of every branch. Everything in the middle is gone with the time and if we are lucky, we see them as fossils. All current evidence suggests that there is only one tree. This tree is commonly known as the "Tree of Life". At the root of this tree is LUCA. It is rather like looking at a spatter of water and ask about the source and strength of the water.

Why is LUCA interesting? The main reason is that it lies at the core of our curiosity - Where we come from? Every civilization or religion has its own creation myth, suggesting that we are universally interested about our origins and from there we can ask, where are we going?

To a certain extend, LUCA is the biological equivalent of Big Bang hypothesis. Much evidence points to its existence but there is no way to prove (at least for the near future). LUCA is thought to be formed at around 3.5 billion to 3.8 billion years ago  (Doolittle, 2000) during the Paleoarchean era, about 700 to 1000 million years after Earth was formed. 3.8 billion years ago was the end of Hadean Eon and before that, the Earth is almost a highly inhabitable place whereas signs of life were found in a rock dated about 3.4 billion years ago (De Gergorio and Sharp, 2003).

So, is LUCA the first life? If so, then LUCA will embed the answer to the question what makes a thing living? What is the breath that breathes the first life? The concept of vitalism was refuted by Friedrich Wohler in 1828 when he made urea without a kidney, as he wrote “I must tell you that I can prepare urea without requiring a kidney or an animal, either man or dog.” However, we know that we cannot take crude extract of cytoplasm, put them in a bottle and call that life... So what is missing? If we know how to make a dead cell living again, a lot of our medical problems can be resolved - dead heart muscles can beat again.

LUCA is suppose to use only dextro-stereoisomers, uses 20 amino acids, uses 4 nitrogenous bases as hereditary material (which we call DNA). LUCA is thought to be existing about 3.5 to 3.8 billion years ago or about 0.7 to 1 billion years after the creation of Earth. This is where the shooting of the foot comes in:- Why 20 amino acids and 4 nitrogenous bases? Why was thymine substituted by uracil in RNA while the other 3 nitrogenous bases remain? Why is the genetic code so uneven - 1 codon for methionine, 6 for lysine and 4 for most of the others? Why you need 3 stop codons and 1 start codon? Was there other LUCA contenders that died and why? Why LUCA? Is LUCA a coincidence?

There is no way of knowing or testing LUCA directly for now, unless we are intending to re-create Earth again. Even then, current LUCA is a coincidence and another very different LUCA may be created. However, there are some experiment and analyses that can be carried out, such as experimental evolution and finding expression invariant genes to take a glimpse of LUCA.