Taxonomy is an attempt to categorize organisms that actually evolved from a universal common ancestor along nearly continuously varying paths. In 2015, the seven kingdoms of life classification model included two prokaryote kingdoms and five eukaryote kingdoms that evolved from a eukaryote common ancestor that formed from prokaryotes through endosymbiosis.
Bacteria: The simplest and most primitive form of life. These small unicellular organisms are prokaryotic, meaning they don’t have a nucleus to store their DNA. Some bacteria including the all important cyanobacteria form filaments with two types of cells, an important step toward multicellularity. Bacteria have formed important relationships with fungi, algae, plants, and animals, sometimes mutual, sometimes not so mutual.
In human terms (https://www.center4research.org/bacteria-good-bad-ugly/):
Bacteria are everywhere, including your entire body. The bacteria in our body weighs as much as our brain: three pounds! Bacteria can be harmful, but some species of bacteria are needed to keep us healthy. The bacteria on our skin, in our airways, and in our digestive system are the first line of defense against foreign “invaders” (pathogens) that can cause infection and other problems.
Bacteria also act as “tuning forks” for our body’s immune system, making sure it’s pitched just right. The immune system shouldn’t be too sensitive or too sluggish: it needs to respond quickly to an infection but it shouldn’t over-react. (If it does over-react and attacks the body itself, the result is an autoimmune disease, such as rheumatoid arthritis, lupus, or MS). Each person has a personalized collection of bacteria, called the microbiome. We acquire our first bacteria while being born, and every day our environment exposes us to more. Some of these bacteria will take up residence inside the body and help develop a robust immune system.
Archaea: This is the second prokaryotic kingdom, but its members have genes and metabolic processes that are more related to eukaryotes than bacteria. Archaea utilize a widely diverse range of energy sources that no other kingdoms use, allowing them to live in environments uninhabitable by others.
Protozoa: The most primitive eukaryotic kingdom in phylogenetic history. Protozoa include a diverse range of unicellular organisms and are thought to be the evolutionary origin of all other eukaryotic kingdoms. Examples of protozoa include amoeba, euglena, and paramecium. Cellular slime molds are particularly interesting because of their ability to behave like a multicellular organisms using important features like cell signaling.
Chromista: This kingdom of eukaryotes acquired photosynthesis independently of the organisms in the plant kingdom which includes red and green algae. Chromists contain different types of photosynthetic organelles and are found in water rather than on land. Examples of chromists are kelp and diatoms. single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles (plastids). It includes all protists whose plastids contain chlorophyll c, such as some algae, diatoms, oomycetes, and protozoans.
Fungi: This kingdom of eukaryotes includes unicellular and multicellular fungi. Unlike the other eukaryotic kingdoms, multicellularity evolved many times from unicellular ancestors and some of the unicellular organisms evolved from multicellular ancestors.
Fungi and animals share a common eukaryote common ancestor. This kingdom is more biochemically and genetically similar to Kingdom Animalia than Plantae. Fungi have a cell wall like plants, but it is made of a different carbohydrate. Yeasts are single celled examples and mushrooms are the aboveground fruiting bodies of multicellular fungi that are otherwise hidden underground. Fungi play a vital role with relationships with bacteria, algae, and plants, without which life on land may never have gained a foothold. Networks of fungal hyphae filaments connect plants and span vast distances.
One possible scenario: Fungi survived and thrived on the decomposing matter that blanketed Earth following the mass extinction of the the asteroid impact 66 mya. Mammals (and avian dinosaurs) being warm blooded are more resistant to fungi and survived and thrived when fungi inherited to the Earth. In fact, warm blooded organisms may have evolved to increase resistance to fungal pathogens. Hibernating bats are susceptible to fungal disease.
Animalia: This eukaryotic kingdom contains some of the most complex organisms on our planet. All animals are multicellular, mobile, and do not have a cell wall. Kingdom Animalia includes mammals, reptiles, and birds, but also simple organisms such as sponges, sea anemones, worms. Animals have numerous vital relationships with each other and with members of other kingdoms.
Plantae: This eukaryotic kingdom includes all land plants and red and green algae. All land plants are multicellular, but some groups of algae are not. This is the only photosynthetic kingdom found on land as well as in water. As previously mentioned, they have important relationships with other kingdoms. For one thing, plant cells cannot fix atmospheric nitrogen or nutrient phosphorus without the help of other organisms, a quirk of the fact that land plants evolved from algae that evolved by endosymbiosis of a single celled cyanobacteria that could not fix carbon and nitrogen in the same cell.
Brain evolution: Where did our brains come from?
Brains have their origin billions of years ago in simple single-celled organisms.
3.4 BYA bacteria began to develop ion channels, membrane proteins that control the flow of ions, paving the way for nerve conduction.
~2 BYA Eukaryote cells developed the ability to make electrical signals when they swam.
600 MYA sponges and comb jellies developed further features seen in modern nervous systems. Sponges organized colonies with proteins used in modern synapses. Comb jellies evolved on of the first neural networks.
550 MYA flatworms developed primitive bilaterally symmetric nerve cords and lights sensors (eyes) which led to early fishes with complex brains inside a protected spinal-cord-like structure.
350 MYA amphibians developed a complex forebrain.
200 MYA mammals entered the scene, further evolving the forebrain.
200,000 years ago, modern humans appeared with every more complex brains and reasoning abilities.
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