LUCA: Last Universal Common Ancestor

All organisms now living have common descent with LUCA. But LUCA is not the origin of life. It’s a common misconception to think that LUCA is the origin of life. But the origin of life existed long before LUCA.

It’s believed the origin of life happened 3.5 to 4.1 billion years ago. Whereas the last universal common ancestor is thought to have lived 3.5 to 2.5 billion years ago.

During the 500 million years that separate LUCA and the origin of life, DNA had to evolve into a somewhat functional system.

For example, DNA included replication enzymes, transfer RNA, and ribosomes at this time. This is because all living things share these same functions meaning they must have been present in LUCA.

An intuition for the last universal common ancestor

All living things originated from a common ancestor called the last universal common ancestor (LUCA). Let’s put this in perspective from our human evolution history:

NEANDERTHALS: Suppose you took your DNA and compared it to a Neanderthal. You’d find that both your DNA is 99.7% identical.
CHIMPANZEES: Next, if you compare your DNA to a chimpanzee, you’d see more differences. In fact, there’s about a 98.5% overlap.
CHICKENS: For a chicken, it’s 60% overlap with your DNA.

As you keep comparing, it never reaches a point where you don’t share any DNA. Simply, we share commonalities in our genetic composition and DNA with all organisms on Earth.

“LUCA is the common ancestor that unites us all. By comparing the genomes of simple bacteria with eukaryotes, LUCA has the most universal genes in all life.”

LUCA thrived in underwater hydrothermal vents

If you look back at Earth’s early atmosphere, it didn’t contain oxygen. So, this means LUCA likely was an obligate anaerobic organism.

LUCA also didn’t rely on other organisms. This is simply because there weren’t a lot around at this point in geologic time.

So, LUCA likely thrived in an iron-sulfur-rich lifestyle in underwater hydrothermal vents. This was the type of environment that could provide water rich in hydrogen, carbon dioxide, and other minerals for it to develop.

LUCA: Last Universal Common Ancestor

The last universal common ancestor is the ancestor of all of life on Earth. It dates back to 3.5 billion years ago when life was just beginning to take shape on our planet.

If you want to learn more about the history of ourselves, the theory of evolution, or biology, then check out some of these courses offered by universities from around the world.

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