History › Earth & early life › First complex cells (eukaryotes)
Multicellular life
simple forms by c. 1.6 billion years ago; animals by c. 600 million· Event· Life & early humans
Mostly agreedGood evidence; some details, dates or numbers uncertain.
Cells began living together as single organisms, with different cells taking on different jobs.
See it on the History map →What happened
Multicellular life evolved many separate times: in red and green algae, in fungi, and in animals. Simple seaweeds appear in fossils about 1.6 billion years ago; animals came much later, by about 600 million years ago. The key step is division of labor: some cells feed, some protect, some reproduce, all sharing one set of genes. The Curious Life map covers this in depth.
Why it matters
It made large bodies, organs and eventually brains possible, opening the path to plants, animals and people.
How we know
Fossils such as 1.6-billion-year-old red algae from India and 1-billion-year-old green seaweed from China; genetic studies estimating when plant and animal groups split.
Still debated
Why multicellular life stayed small and simple for roughly a billion years before animals appeared is debated.
Connections (2)
▸First complex cells (eukaryotes) gave rise to Multicellular lifeMostly agreed
The connection
Eukaryotic cells had the size, energy and genetic tools to stick together and specialize. Some colonies began dividing tasks: some cells fed, others reproduced. Over time such colonies became single organisms, as red algae, green algae, fungi and animals each evolved multicellular bodies separately.
When and how
In the oceans, beginning at least 1.6 billion years ago with red algae; animals by about 600 million years ago.
How sure are we?
All complex multicellular organisms are eukaryotes; fossils of multicellular algae appear after the first eukaryote microfossils.
Debates and open questions
Why complex multicellular life arose only among eukaryotes, and only a handful of times, is still debated.
▸Multicellular life led to Ediacaran biota: the first large animalsWell documented
The connection
After about a billion years of mostly small, simple multicellular forms, larger and more complex organisms appeared. The Ediacaran creatures were among the first big enough to see without a microscope, some over a meter long, showing how far multicellular life had come.
When and how
On shallow and deep seafloors from about 575 million years ago; named for the Ediacara Hills, South Australia, where geologist Reginald Sprigg found them in 1946.
How we know
Fossils show a clear sequence: microscopic and small multicellular forms come first, then the large Ediacaran organisms.
Debates and open questions
How Ediacaran organisms relate to earlier forms and to modern animals is still unclear.