https://www.quantamagazine.org/primitive-asgard-cells-show-life-on-the-brink-of-complexity-20230411/
Eukaryotic cells have organelles (such as a nucleus, mitochondria, ribosomes, etc), they have the ability to specialize (heart, liver, lung, brain, etc), and they (obviously) have the ability to bind together to form complex organisms.
Contrast that with the two other branches of life, bacteria and archaea. A complete bacterial or archaean organism consists of a single cell. This cell consists of a cell wall, cytoplasm, coils of DNA, some mechanism for extracting energy from the environment, and not much else. They (especially archaea) are masters at survival in extreme, harsh environments, and they were almost certainly the first life on earth.
Did eukaryogenesis happen as in independent event (unlikely), or did eukaryotes evolve from archaea? If the latter is true, are there any transitional species, archaea or bacteria that are "half-way" to eukaryotes?
There are a couple of hundred proteins that are common to all eukaryotes. About 15 years ago, deep in the sea-floor near hydrothermal vents where the conditions are too harsh for eukaryotic animals to survive, researchers discovered DNA for many of those proteins. Among the genes discovered was the gene that encodes the protein "actin", most well known for forming the cytoskeleton of eukaryotic cells. The existence of the genetic material for key eukaryotic proteins hinted (ok, shouted) that there probably exists some form of bacteria or archaea that can survive near those hydrothermal vents, but which contain the proteins that, in the course of evolution, would come to define all eukaryotic life.
Deep in the muck of the sea floor, do those single celled creatures from whom all eukaryotic life is descended still exist?
Read on 🙂
It's a long article, but an absolutely outstanding piece of completely accessible writing on a very technical subject.
Original paper in Nature: