Final answer:
The Last Universal Common Ancestor (LUCA) is considered the last common ancestor of all current life, not the first cell. It survived due to its evolutionary success and helped establish a universal genetic code through horizontal gene transfer, becoming a fundamental evolutionary bottleneck.
Step-by-step explanation:
The Last Universal Common Ancestor (LUCA)
The concept of the Last Universal Common Ancestor (LUCA) is pivotal to understanding the lineage of all living organisms. The LUCA is not considered the very first cell to have emerged on Earth but is rather thought to be the last common ancestor to all existing cells. While there likely were many early cells, it is believed that LUCA's lineage was evolutionarily successful, outcompeting other life forms, which subsequently became extinct. This high level of evolutionary success led to a single, universal genetic code and translation machinery, which is evident in all organisms alive today. This period, postulated to have existed around 3.5 billion years ago, involves a simplified prokaryotic cell that lacked a nucleus and other membrane-bound organelles.
One crucial aspect of the LUCA hypothesis is the impact of horizontal gene transfer (HGT), which allowed for extensive sharing of genetic material among early cell populations. This genetic exchange is believed to have been critical in the evolution of the LUCA, leading to a universal genetic code that facilitated further complexity in cellular life.
It is important to note that the universal genetic code and the conservation of translation machinery are some of the strongest evidences for the existence of LUCA. Any early cells or proto-cells that existed before LUCA would have had very different evolutionary pressures and mechanisms, with LUCA representing a fundamental evolutionary bottleneck. The properties of life we see today are the result of the evolutionary pathways that evolved from the LUCA, leading to the diversity of life on Earth.