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The family tree of life
- Faith Poh
- Oct 1
- 7 min read
Tigers, cats, and dogs. Two are obviously more related than the other. But what about hamsters, rats and hedgehogs? How are mushrooms more closely related to us than trees? Are viruses related to bacteria?
These are questions you may have pondered. Googled, even. This guide is a quick introduction to the various groups of life - encompassing viruses, bacteria, plants, mushrooms, and animals (feel free to skip to whichever section!). This article will answer some common questions and have my favourite fun facts.
Phylogeny and Paleontology
Phylogeny is the study of the evolutionary relationship between organisms, and is shown in a phylogenetic tree, like the image below, or more often like the other images in this article. Paleontology studies extinct life, especially through fossils. Understanding how organisms evolved can inform how they could evolve and adapt in today’s warming climate, better equip us to assist them in this transition, and is generally just fun to learn about.
The next pandemic: Viruses
They are not considered alive, since they have no cells*. Instead, they are simply genes and proteins with a protein covering (capsid). They need another cell to reproduce. As such, they are distinctly different from bacteria, which are actual cells that can reproduce by themselves, and only some parasitise other cells to obtain nutrients. Most viruses are microscopic, but some reach around 1mm, such as the mimivirus and pandoravirus - they can even be infected by viruses.
Below are some hypotheses about the origin of viruses. Some posit that they come from cells!
Virus evolution research is difficult, because there are only a few genes, so there is less to compare, and their genes change easily and frequently. That’s why flu shots come so often. When the gene changes, the protein also changes, and our body needs a new vaccine to recognise this new protein. It's also why viruses have potential to become the next big pandemic, because they are adaptable and can jump from species to species. (Of course, bacteria are also a growing threat, due in part to growing antibiotic resistance.)
*according to the cell theory, which posits that all living organisms have cells. NASA has its own definition of life, but viruses also don’t fit that definition.
The BAEs: Bacteria, Archaea and Eukarya
People don’t actually call them BAEs.
All of life falls under BAE. Most are single celled**, but a few in Eukarya achieve complex multicellularity including plants and animals. Unicellular organisms do everything under the sun: use light to make food, prey on other cells (some even have “mouths”), parasitise, etc.
The bacteria and archaea are called prokaryotes, and eukarya are eukaryotes. This distinction is based on cell structure, most notably eukaryotes having a membrane surrounding the DNA (called the nucleus) and a mitochondria (powerhouse of the cell), and prokaryotes not having them.
The current consensus is endosymbiosis: the mitochondria and chloroplast were ancient cells (bacteria) that evolved to live inside another cell (archaea)
Seen in the similarity in ribosome (protein producer) structure in current-day bacteria and mitochondria/chloroplast
Discovery of Lokiarchaea in 2015 which has proteins unique to eukaryotes (named due to its location near Loki's Castle, a hydrothermal vent)
This is the relationship within eukaryotes (2019), aka the Eukaryotic Tree of Life.
Still up for debate, especially since these groups diverged a VERY long time ago
The ones I’ve labelled are all the complex multicellular organisms**, which are bigger and we can see. Everything else is called a protist.
** there are simple multicellular organisms, which has evolved numerous times, ranging from a colony (slime mold, volvox), to filaments (cyanobacteria)
Photosynthesisers: Plants
Bread, rice, potato, tomato. All are flowering plants, which currently dominate the planet. They, alongside algae and other protists, carry out photosynthesis: creating chemical energy from light energy. Virtually every other organism gets their energy from eating plants, or eating plant eaters.***
The angiosperm phylogeny group (APG) releases a relationship chart of flowering plants every few years, latest 2016. They might release a new one soon, given that Kew Botanic Gardens released a paper about the flowering plant phylogeny in 2024, part of their Plant and Fungal Tree of Life initiative (There are over 200 authors in this paper - it was a huge collaboration with other scientists, botanic gardens, and related projects).
Land plants: called embryophytes, because they nurture the young embryo (sporophyte generation) within the adult plant (gametophyte generation). Sporophytes and gametophytes have got to do with alternation of generation which is… under the scope of another article!
Bryophytes: liverworts, mosses, and hornworts. They have no method to transport water or food, so they are rather small.
Tracheophytes: seed plants, club mosses and ferns. They have vascular tissue to transport water and food, much like our circulatory system, giving rise to the first trees!
Seed plants: protect and provide food for the next generation in a seed, as opposed to a spore with no food storage.
Gymnosperms: non flowering seed plants, such as conifers and ginkgos.
Angiosperms: flowering plants. The most dominant lineage.
***Photosynthesis is energy from light. The alternative is chemosynthesis, energy from inorganic compounds. This is found in organisms living near hydrothermal vents, giving birth to the hypothesis that life emerged from such vents.
Understudied understory: Fungi
Less than 10% of an estimated 2-3 million species have been described. Historically, fungi have been ignored, owing to their small size. They make up our mushrooms, mold, and yeast, and drugs derived from fungi include penicillin - the first antibiotic.
On top of frequently being (saprotrophic) decomposers and parasites, fungi are known for their mutualistic relationships. Lichen comes from algae, bacteria, and fungi collaborating, and mycorrhizal fungi interact with plant roots, giving water in exchange for nutrients. Orchids rely on fungi so much that their seeds no longer have food storage, instead using fungi for nutrients to germinate.
This image is already outdated, but still good enough.
It’s me, hi: Animals
Animals are said to have evolved before the Cambrian explosion (500 million years ago) - which is a period of quick diversification of animals, and all modern animal body plans emerged then.
Notice how in the left image, the sponges (porifera) branch off first. The sponges and comb jellies (ctenophore) are contenders for this position. It seems the consensus is currently on comb jellies, which has been further supported by a 2023 study about the similarities in chromosomes.****
The right image contains all the chordates. Chordates have 5 common characteristics, seen below, and an endostyle which evolved into our thyroid. This legacy can be seen in how the human embryo has a tail and gills during its development. However this has been greatly exaggerated, and in actuality embryos only look similar at a specific point in time, and are mostly very distinct.
****Our genes are on the chromosome, kind of like lego bricks stuck together. The “lego bricks” can be rearranged and passed down to the next generation, so the most similar chromosomes are the most related organisms.
Then, from the tetrapods (literally four legs), came the land animals, explaining why all land animals have 4 limbs. In birds and bats, their wings are arms. The “walking fish” Tiktaalik is a well-known transition fossil.
From there, we get the amphibians, reptiles, and mammals. Reptiles and mammals have embryos surrounded by the amnion, which produces a liquid that protects it and allows it to survive without being in water.
I added a mammal phylogeny tree, in case you're interested, but you can actually look it up yourself, especially since it can get very detailed. (Can you find the humans? hint: search what family humans are in, and think about which animals are closely related to humans.)
Interactive tree of life | |
Geologic time, methods to study paleontology, animals before chordates | |
Flowering plant phylogeny | |
Fungi | |
Insect identification guide, insect phylogeny | |
Marine species | |
Bird identification, bird caretaking |
References
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