Evolutionary Tree of Life | Episode 1 - Early Life, Invertebrates & Fish

Hi. This is Matt Baker. One of the things that  this channel is best known for is its family trees.

Well, today I'm going to show you the  ultimate family tree — the one that connects every single living thing on our planet: the  Evolutionary Tree of Life. Exactly 10 years ago, I created this similar chart and ever since  then, it's been one of UsefulCharts’ best selling posters. Well, over the last few months,  I've been working on a major update — not only improving the design but also making sure  that it lines up with the latest research.

And today I'm happy to announce that the new  version is finally available. If you want to get a copy, just head over to our website  [UsefulCharts. com](http://UsefulCharts.

com) or click the link in the description  or pinned comment. While you're there, take note that — for the first time ever — we've  made this particular poster available in two sizes. There's our regular size (24 by 36 inches)  but there's also a jumbo size (32 by 48 inches).

Okay, so today’s video is going to be the  first in a series of videos that I'll be doing on evolution, mostly explaining the  Tree of Life chart in detail. In Episode 1, I'll be focusing on the very earliest forms  of life and how they ended up leading to the three major kingdoms that most people  are familiar with: Plants, Fungi, and Animals. From there, I’ll be going through  invertebrates, such as Molluscs and Insects, as well as the earliest type of  vertebrates: fish.

In future episodes, we’ll then take a look at reptiles & birds,  mammals (including humans), the Plant Kingdom, and then finally I’ll be doing a bonus episode on  the evidence for evolution. Okay, let’s get to it. [New Intro] At the very bottom of this chart is LUCA,  which stands for Last Universal Common Ancestor.

This is the single celled organism  from which both bacteria and archaea evolved, as well as all other living things on the planet.  Now, as to where LUCA and its ancestors came from, well, that is a question that falls outside of  the theory of evolution and therefore I won’t be addressing it in this video. However, this doesn’t  mean that scientists have absolutely no clue about how the first living cells arose from non-living  matter.

There are actually several theories out there and if you’re interested in learning about  them, just do a search for the term abiogenesis. I should also point out that I’ve put viruses  over here, unconnected to the main tree. That’s because we’re still not sure exactly how viruses  are related to life.

They may represent a stage before the emergence of life or they might be  the result of some DNA or RNA escaping from a living cell. Either way, the main difference  between anything living and a virus is that life can reproduce on its own, whereas a virus  needs a living host in order to replicate. Nowadays, viruses are categorized into realms, of  which three are shown on this chart.

Duplodnaviria includes viruses that are based on a double  strand of DNA (hence “duplo”). These include the viruses that cause Herpes, Mono, and Chicken  Pox. Varidnaviria includes various DNA-based viruses such as the virus that caused smallpox as  well as the closely related Monkeypox.

However, most viruses that you’re likely to  be familiar fall under Riboviria, because they are dependant on RNA rather than DNA.  This includes the viruses that cause the common cold as well as those that cause the flu (which  is short for influenza). Take note that there is in fact a difference between a cold and a flu  (a flu being the more serious of the two).

But, of course, more serious than both a cold or a  flu is Covid, which is caused by a coronavirus. Coronaviruses fall under the Nido-virales  category. Finally, take note that Ribo-viria also includes the viruses that cause  measles, mumps and rabies as well as HIV.

Okay, we’re now ready to move up from LUCA to  the earliest branches of life. 10 years ago, when I first made an evolution chart,  it was thought that life initially went in three directions, which is why the previous  version had three domains: Bacteria, Eukaryote, and Archaea. However, nowadays, the leading  theory is that there should be only two domains: Bacteria and Archaea (with the Eukaryotes evolving  out of Archaea).

Let’s look at Bacteria first. Bacteria is the type of single celled  life that we’re most familiar with, because, like viruses, they cause a  lot of diseases. Take, for example, Streptococcus (which causes both strep throat  and pneumonia) or Staphylococus (which people often get in wounds).

Both of these bacteria  belong to the Bas-illota phylum. An even larger bacteria phylum is Pseudomonadota. It  includes the germs that cause E.

coli, cholera, salmonella, meningitis and, worst of all,  the Bubonic Plague, aka the Black Death — the most deadly pandemic in all of human history. But not  all bacteria is bad. There’s also good bacteria, called probiotics, such as lactobacillus, which  is used to make yoghurt and is good for our digestive systems.

There’s also Pelagibacteria  (Pelagus being Greek for “of the Sea”). These bacteria live in the ocean and are super  important for the earth’s overall ecosystem. Archaea are far less familiar to the  average person.

They were initially lumped together with bacteria but are now  understood to be quite distinct. In fact, they include some of the most extreme forms  of single celled life, such as those that live in super hot environments (called  Thermophiles) and those that live in super salty environments (called Halophiles).  However, Archaea also includes a proposed super-phylum called Asgard, named after  the home of the gods in Norse mythology.

It is from Asgard cells that the very first  Eukaryote cell is thought to have developed, around 2 billion years ago. Now, Eukaryote  cells differ from Bacteria and Archaea cells in that they are much larger and more complex, being  comprised of many different parts — most notably, a nucleus (which is where the cell’s  DNA is located). This contrasts with Bacteria and Archaea cells which have DNA  floating around in the middle.

Another part of a Eukaryote cell that you might  be familiar with are the Mitochondria, which are kind of like little  energy factories. Interestingly, these came to exist within Eukaryote cells  via a process called Endosymbiosis. Basically, a bacteria cell (similar to those Pelagibacteria  I mentioned earlier) went INSIDE an Asgard cell to create a sort of “super” cell.

One example of  these early type of “super” cells are amoebas. However, over time, these new kind of cells  started to join together to form multi-celled organisms as well — such as brown algae,  which is now placed in the S. A.

R. supergroup. But then there was yet another endosymbiosis  event, around 1 billion years ago.

This time, a type of cyanobacteria entered a eukaryote  cell to create archaeplastids, which have yet another special cell part called plastids. The  most famous type of plastid is the chloroplast, which is used by plants to convert energy  from the sun into a type of energy that can be transferred to other living things. As  humans, all of the energy that we have comes from eating plants or from eating animals  that eat plants or — in rare cases — from eating animals that eat animals that eat  plants.

Take note that some types of brown algae did not originally have plastids  but perhaps inherited them from red algae. Now, take note that all of these early  Eukaryote lifeforms exist OUTSIDE of the three main kingdoms, which are Plants, Fungi, and  Animals. At one time, these early Eukaryotes were placed in a fourth kingdom, called Protists,  and then later, they were divided into a bunch of smaller kingdoms but nowadays, the exact  classification has been kind of left up in the air because scientists are still trying to  figure out exactly how everything pieces together.

Another big thing that has only been discovered  quite recently is that Fungi are actually more closely related to Animals than they are  to plants. This is because both Fungi and Animals evolved around a billion years ago from  early Opisthokonts, whereas plants did not. The term Opisthokont comes from a combination of  Greek words that mean something like “rear pole”.

That’s because simple Opisthokonts have  these sort of tail-like things called flagellum. Now, for the rest of this episode as well as  Episodes 2 and 3, I’ll be focusing entirely on the animal branch. However, take note that in Episode  4, I will be coming back to talk about both plants and fungi — so stay tuned for that.

Anyway,  the earliest types of animals probably looked something like sea sponges, which to be honest,  don’t really SEEM like animals (even though they are). You see, despite the fact that sea sponges  don’t move, they are in fact animals because they have animal cells, just like you and me. Corals,  which belong to the same phylum as jellyfish, also don’t move but they at least have a very  simple nervous system and it is the nervous system that eventually allowed animals to evolve the  ability to move, react, and eventually, to think!

But I’m getting ahead of myself. The other big  thing that developed early on in the animal branch is bilateral symmetry. You only have  to look in the mirror to understand what this is.

It’s the reason why you have two eyes, two  ears, two arms, two legs, et cetera. Basically, if you draw a line down the center of your  body (or that of most animals), you get two sides that mirror each other. With the emergence  of Bilateria, animals went in two very different directions.

There’s the Protostome branch and  the Deuterostome branch. These two terms mean “Mouth-first” and “Mouth-second” referring  to the different ways that animal embryos can develop. Most animals have a digestive system with  a mouth on one end and an exit hole on the other.

Protostomes develop the mouth first and then the  exit hole, whereas Deuterostomes do the opposite. The other big difference is that the Protostome  branch went on to produce lifeforms with an exoskeleton, or outer shell (like insects,  for example) whereas Deuterostomes went on to produce lifeforms with an endoskeleton (meaning  that they have their hard parts, called bones, on the inside). Let’s look at Protostomes first. 

The earliest types of Protostomes were the ones that don’t have exoskeletons, such as flatworms  and earthworms. But then came Molluscs, which do, such as snails and clams. The most interesting  type of molluscs are the cephalopods, which include squid and octopuses.

Their ancestors  would have had shells too but at some point, they lost them. However, they gained something  potentially better: eyes very similar to our own (which is a great example of something called  convergent evolution — these are instances where similar structures evolved independently of  each other, on different branches of the tree. Octopuses in particular are also among the most  intelligent non-human animals on the planet, which just goes to show that there’s no one  branch on the tree that is necessary more advanced than any other.

Now, while I’m here,  I’ll point out the fact that most living things can still be categorized according to the very  old naming system developed by Swedish biologist Carl Linnaeus back in the 1700s. Linnaeus is the  one who developed the ranking system that starts with Kingdom and then proceeds through Phylum,  Class, Order, Family, Genus and Species. So, to make things clear: many species make up a  Genus; many Genera make up a Family; many Families make up an Order; many Orders make up a Class,  many Classes make up a Phylum, and many Phyla make up a Kingdom.

Now, since the 1700s, it’s  become clear that things are actually much more complicated and that’s why there are often other  category names inserted between the main ones, such as Bilateria and Protostomia. In these  cases, those divisions are simply called a clade. Okay, next I want to start back at the Protostome  node and proceed up this time, towards the insects.

But first I want to point out this event  here: the Cambrian Explosion, which occurred around 540 million years ago. You see, this is  the point in which animal life started to go in a bunch of different directions, as evidenced by the  wide variety of fossils that can be found AFTER this point. However, it’s important to remember  that creatures with bones or shells leave better fossils so it might just be that 540 million years  ago was when shells and bones became more common.

Regardless, it was around this time that the first  tactopods evolved (tactopod meaning “organized feet”). This category includes tardigrades  (which look like tiny bears wearing hazmat suits) but more importantly it includes the massive  Arthropoda Phylum, which has all the spiders, insects, and other creepy crawly things. These  were the very first animals to leave the water and crawl on to land, although obviously some  (like crabs and lobsters) still live in the sea.

The very first arthropods would have looked  something like this — kind of like a millipede. Note that it has a segmented body and lots  of legs. All modern arthropods have the same basic body plan but with modifications. 

For example, insects evolved to have only six remaining legs — however another six of their  “former legs” evolved to serve as mouth parts. In addition to this, most of the segments fused over  time so that insects are now left with only three: the head, thorax, and abdomen. Contrast this  with spiders, who, as you probably know, have eight legs and only two segments.

But what  you probably didn’t know is that most of their legs evolved from the same appendages that now  serve as mouth parts in insects. Spiders’ two mouth parts (or fangs) actually evolved from  what used to be their antennae and two of their “former legs” evolved to become pincers (which  are much larger on the closely related scorpions) Another thing to note is that crabs are  actually more closely related to insects being that both of these groups evolved  from early crustaceans. Insects however fall under the category of hexapods, because, like  I said, they all have six legs.

Some insects also developed wings early on (such as dragonflies) but  regardless of whether an insect crawls or flies, technically-speaking, most insects are  not bugs. Although the word “bug” is used casually to refer to any creepy crawly  thing, from a scientific point of view, only those insects belonging to the Hemiptera  Order are “true” bugs. The largest category of insects is actually the Holometabola  Superorder.

These are insects such as beetles and butterflies that go through a  metamorphosis involving four stages: egg, larva, pupa, and adult. Included in this group is  the Hymenoptera Order, which includes both ants and bees, arguably some of the most intelligent  insects due to their complex social structures. Okay, let’s now go all the way back down  to Bilateria and follow the Deuterostome branch instead.

First off, you’ll notice starfish,  which you might not think of as having bilateral symmetry but which actually do, if you think  of it this way. However, the most important Deuterostome phylum is Chordata. Chordata includes  lancelets as well as all the vertebrates (which are animals with backbones protecting a column  of nerves that run down the back).

The earliest vertebrates would have looked similar to lampreys,  which have a mouth full of teeth but no jaw. Now, once the jaw evolved, things went in two  directions. On the one hand, we get fish with skeletons primarily composed of cartilage  (like sharks and rays); and on the other, we get fish with skeletons primarily made of bones, which  are much harder.

If we follow this bony fish line, we’ll see that things once again split in two.  We get ray-finned fish and lobe-finned fish. The vast majority of fish that you’re likely  familiar with are ray-finned, meaning that they have simply fins like this, that flap, helping  the fish to swim in the water.

All ray-finned fish belong to the Actinopterygii class, which contains  about 50% of all known vertebrate species. Most of these, in turn, are Teleosts, which can then be  broken down into two main claydes: the Otocephala and the Euteleostei. Otocephala includes catfish,  sardines, tetras, and carp (with the carp order being the one that goldfish and koi belong to, as  well as minnows) whereas Euteleostei includes cod, salmon, and the percomorphs.

Percomorphs  are, evolutionary-speaking, “newer” fish, in that they mostly developed after the  extinction of the dinosaurs. They include edible fish like tuna, halibut, and perch  but also popular aquarium fish like guppies, cichlids, and bettas. And then there’s  one of the strangest fish of all: seahorses, named because they have  upright heads that look like horses.

Let me tell you about lobe-finned fishes. Although  far less common, they are super important in that it is from the lobe-finned fish (or Sarcopterygii)  that all land vertebrates descend. So, as you can see from this diagram, lobe fins are more complex  than ray fins.

They have bones that look more like little limbs — which is basically what they are.  Although lobe-finned fish just use them to flap, and hence swim, this would later allow certain  creatures to do a bit of crawling in shallow water as well. The main lobe-finned fish that  are still around today are the coelacanths, and the lungfish.

And it is with them  that we are going to end today’s video. Next time, we’ll continue up through the  tetramorphs to the earliest tetrapods, who climbed on to the land and eventually  evolved into amphibians, reptiles, dinosaurs, and so on. Okay, don’t forget — if you want to  get a copy of this brand new chart as a poster, you can do so right now by visiting our website  [UsefulCharts.

com](http://UsefulCharts. com) or by clicking the link in the  description or pinned comment. Thanks for watching.