tend to tweet about a lot of serious stuff¶

I tend to tweet about a lot of serious stuff. How about some fun, uncontroversial, totally apolitical science?

Let's talk about the kingdoms of life!

Modern phylogeny focuses on the evolutionary history of organisms, rather than their apparent traits. https://t.co/a9uSthcaXr All living things on Earth evolved from a single common ancestor. Technically, you are 1,000th, 1 millionth, or 1 trillionth cousins with every human, every dog, every tree, and every one of the billions of bacteria you kill every morning when you brush your teeth! https://t.co/deSXkoUYoV Scientists tend to group life into 3 kingdoms: bacteria, archaea, and eukaryotes. We have a lot of evidence to suggest that this latter category (which includes all animals, plants, and fungi) is just a special kind of archaea that swallowed mitochondria without digesting them! https://t.co/wQpCGG2LXw This is called endosymbiosis: a symbiotic relationship between different species, one of which is inside the other. Think of our gut bacteria; they digest food we can't, giving us access to more nutrients, and they get a constant supply of that food, courtesy of their giant host! https://t.co/kldNTh2k5u Since mitochondria are likely descended from bacteria, this would mean that our kingdom is the result of the union between the two other kingdoms!

Plants likely even went one step farther and later swallowed another bacteria, which gave them the ability to photosynthesize! https://t.co/PO9f7J2cG9 The divergence of plants from other eukaryota is estimated to have happened 1.5-1.8 billion years ago. About 1-1.2 billion years ago, fungi and animals started to diverge. Yes, you're more closely related to a mushroom than a tree! We have a lot in common with our fungal cousins. Even before plants gained photosynthesis, they stored their carbohydrate energy in the form of starch, while fungi/animal ancestors used glycogen. This might sound trivial, but it's a huge difference! Starch is more rigid, so glycogen-users tend to be more flexible and mobile. https://t.co/STnhYZtMoB Plants adapted their starch energy storage to evolve cellulose, which is really rigid, to form their protective cell walls. Fungi and animals adapted glycogen to form chitin--our own cellular armor. Many animals (including mammals) have since evolved away the use of chitin. https://t.co/sYnfia1y1V Everything we've talked about so far has been single-celled life. It's hard to pin down when true multicellular life emerged, but it's pretty clear that all three branches of eukaryotes--and some bacteria and archaea--evolved multicellularity independently! It's not as hard as you might think to make the leap from single-celled to multi-celled organisms. Unicellular organisms have formed stuck-together blobs called colonies for billions of years. The molecular prerequisites for shifting to multicellularity were already there. https://t.co/Uswk7aCw3J One striking example is the algal genus volvox. It forms blobs that have an outer layer responsible for obtaining nutrients for the "colony," and inner cells whose only job is to reproduce. This is true multicellularity, because the outer cells cannot reproduce on their own. https://t.co/C1fwOBNQZo As far as we can tell, multicellular life emerged independently DOZENS of times in eukaryotes, although all animals seem to be descended from one multicellular ancestor.

We don't know what the first animal was, but the earliest animal fossils we have are likely sponges. https://t.co/VBJIf1ZNmN Obviously, as humans, we care a lot about the evolution of animals, so I might make a specific thread on animal evolution later. Needless to say, a lot has happened to animals in the past 700-600 million years, although we still represent only 0.4% of all biomass on Earth! https://t.co/eYEfjd7AIh The history of life on Earth is messy and still not fully-understood. But it's really interesting to think about where we came from and what changes led to us being here!

“For a biologist the alternative to thinking in evolutionary terms is not to think at all.” -Peter Medawar https://t.co/Ssoaoswfua