We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Biology

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is the Three-Domain System?

Mary McMahon
By
Updated: May 21, 2024
Views: 71,534
Share

The three-domain system is a method for classifying cellular life which was initially proposed by Carl Woese in 1990. While the three-domain system met with some initial opposition, it has since become widely accepted, thanks to scientific discoveries which have supported Woese's proposal. Under the three-domain system, all cellular life can be divided into three domains: Archaea, Bacteria, and Eukaryota, and each domain can be further divided into kingdoms, phyla, classes, and so forth.

This classification system distinguishes between eukaryotic organisms, organisms which have cells which include a nucleus, and two types of prokaryotic organisms, organisms with cells which lack a nucleus. Initially, Archaea and Bacteria were both lumped together as prokaryotes, although each group had its own kingdom. Woese argued that Archaea and Bacteria were so distinct that they actually belonged in separate domains, not just separate kingdoms.

The differences between Archaea and Bacteria primarily have to do with complex genetics. When Woese first published his proposal, genetic research seemed to suggest that the two kingdoms were descended from a common ancestor, and that they were similar enough that they did not require separate domains. As a result, the three-domain system was initially viewed with skepticism.

However, further research indicated that Woese was actually right, and that these organisms were so genetically distinct that they needed their own domains. Archaea and Bacteria are both prokaryotic, but their cellular structures are markedly different, and they have very distinct ribosomal RNA, indicating that these domains diverged a very long time ago, and are largely unrelated. The three-domain system for classifying organisms seems to be more accurate than previous systems now that evidence to support it has been discovered.

Within Archaea, there is only one kingdom, also called Archaea. The Bacteria domain also hosts only one kingdom, known as Bacteria. Eukaryota can be divided into four kingdoms: Animals, Plants, Fungi, and Protists. Within each domain, there is a huge diversity of life, ranging from extremophilic Archaea which thrive in environments which would kill most other life on Earth to fragile tropical orchids in the Plant kingdom.

This system is especially important to people who study prokaryotic organisms, since the three-domain system underscores the difference between Bacteria and Archaea. Researchers typically specialize in one or the other, using genetic research to learn more about the organisms they study. Some people still use the two-empire system, which divides cellular life into Prokaryota and Eukaryota, and then into respective kingdoms, but this is becoming increasingly rare.

Share
All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By miriam98 — On Jun 25, 2011

@David09 - I think I know what you’re talking about; the book you’re referring to stirred some controversy.

But you raise a good point-when Darwin was around, there was no such thing as molecular biology. A simple cell was viewed as a simple cell. With the power of the electron microscope, we can see that it is anything but simple, and that in fact molecular biology would suggest a different family tree than what Darwin could have anticipated.

After all, his classifications were made as a result of purely visual observations, nothing happening at the molecular level.

By David09 — On Jun 23, 2011

It’s remarkable that this classification of living organisms was suggested as late as 1990. That’s quite a long time after Darwin proposed his theory of Evolution through Natural Selection.

Given that Woese’s theory met with some initial skepticism, because it conflicted with existing assumptions about how different organisms related to one another in the evolutionary tree, I think it’s possible that there are other assumptions about evolution that may not be true as well; such as, did it even happen?

I ask because I read a book by a molecular biologist who claimed that as a result of his studies, the traditional taxonomy suggested by evolution was completely wrong, at the molecular level that is.

His book was not met with a warm reception, but I sometimes wonder if he's right, given his field of study.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
Share
https://www.allthescience.org/what-is-the-three-domain-system.htm
Copy this link
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.