Previously in our journey from the birth of life to us Homo Sapiens, we only got as far as, well, the birth of life. We explored the two domains that started life as far as we know, from at least 3 billion years ago: Archaea and Bacteria.

There's obviously a lot of contention as to when life really triggered, but the more we look, the earlier things got, possibly from 4 billion years or more ago - astonishing given the Earth's 4.8 billion year life span.

As discussed, bacteria and archaea are strikingly similar morphologically, but their very structures are founded on completely different biochemical grounds. As it happens, Archaea is actually more closely related to us eukaryotes than bacteria, acting as a kind of gateway between the two domains.

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Though much of the earth's biodiversity can be found in the smaller, prokaryotic domains, it's the eukaryotes that are more apparently diverse. This is where we continue our search for humans.

Unikonts & Bikonts

Our first stop is about 1.4 billion years ago (Ga). Eukaryotes could have evolved as far back as 2.7 Ga, but strongest evidence shows Unikonts and Bikonts to be the earliest branch of eukaryotic life.

Unikonts are single celled eukaryotes with one flagella - microscopic tails that help little things swim around - and Bikonts, as you can guess, are those with two flagella.

Why are we talking about these little swimming ancestors? Well, because together, they are suggested to be the root of us all. Where Unikonts are said to be the ancestors of animals, fungi and Amoebozoa, Bikonts are the ancestors of plants and similar in kind. This so far is unproven, but the evidence so far points this way.

Gene Fusion

In genetics, genes can mutate, chromosomes can form abnormalities, and these things can occur in a variety of ways. Sometimes, through translocation, deletion or inversion of chromosomes, genes can fuse together as shown on the right here.

This is where Unikonts are set apart from bikonts an bacteria. Unikonts have gone through triple gene fusion that code for specific enzymes which demonstrate a shared ancestry between both Opisthokonta (animals and fungi) and Amoebozoa.

Amoebozoa

Amoebozoa, as the full taxonomic group is called, consists of about 2,400 known species of eukaryotic life fitting into the kingdom of 'protista'. Often, amoebozoa are grouped together with the unikonts, or described as a sister group. They typically are unicellular in nature, such as the more familiar 'amoeba' but there are known to be some slime molds which are indeed comparatively large and multicellular

In case you're getting lost, I found this picture puts things together very clearly:

It may also make more sense to you now when you hear that often-heard factoid 'Did you know, Fungi are more closely related to us than plants??'

Naturally, it gets more complicated than that, but not today.

Controversy

As you may have guessed from the tone of this post, this is not all cut and dry, black and white. There's a whole lot of blurry grey areas where debate still thrives. According to a paper from 2012 you can check out below:

It has not been determined whether the Apusozoa (apusomonads and ancyromonads) or the Amoebozoa form the sister group to opisthokonts, nor to which side of the hypothesized unikont/bikont divide the Apusozoa belong

That last part I found quite interesting. We don't know if something is a unikont or a bikont - An animal, a plant, a fungi, huh? So what's an apusozoa?

Apusozoa

These critters are tiny, bacteria feeding eukaryotes that live in soil and water. The proposition to date appears to be that they belong in the obazoa phylum, which is proposed to be a sister group of those amoebozoa. By combining the Obazoa group in which the apusozoa reside with the amoebozoa of the slime molds and amoeba, you get yourself the Unikont group.

We quite literally come from slime, if the research works out.

Too long, didn't read

From all this, we know that we don't want to go the direction of the Bikonts. They lack that triple gene fusion that led to us via the Unikonts. Travelling down the tree's branches, we find at this point there are still a full 1.6 million species to narrow down. But for now, what we know is this:

• The Domain Eukaryota developed from the domain Archaeon
• The first Eukaryota are 1-flagella and 2-flagella organisms; unikonts and bikonts that evolved at least 1.4 billion years ago
• Bikonts are ancestors of plants and others, Unikonts are ancestors of fungi, amoebozoa, and animals - us
• Protists were the first supergroup of Eukaryota
• Unikonts and Bikonts share a blurry line that remains uncertain to date, but it's fairly safe to say we're not plants.

Last words

I hope you all feel as enlightened as I am. This seems far more enlightening to me than those 23 & me saliva lineage tests, at least! So, fellow Unikonts, put your tongue away and revel in our shared, slimy ancestry.

We still have a long way to go.

All other images CC0 Licensed

References: _{Molecular phylogeny of unikonts: new insights into the position of apusomonads and ancyromonads and the internal relationships of opisthokonts. | Apusozoa | Obazoa | Amoebozoa | Gene Fusion | Unikonts | Bikonts}