Who are “we”? Politically, I like to say, “I identify as human.” 1 As biological beings, though, our identity does not begin or end with being human. We inherited our genes from ancestors that go back uninterruptedly to the dawn of life. In this chapter, they matured from bacteria to back-boned animals! How did we come to inherit bodies that eat, breathe, and have sex?
Some of these basic life functions are older than bodies themselves. After bacteria, the next breakthrough lifeform was our cell type, the eukaryote. The first eukaryotes, protists, are introduced in Section II. This was the generation that actually did invent sexual reproduction, the subject of Section III.
Long-term biological change is called evolution. Section IV will discuss the fundamentals of sexual evolution before Section V surveys the specific biohistory of our earliest animal ancestors. Most major body features, from the skin to the brain, appeared in the Paleozoic Era at the end of this timscale.
The developing brain takes us directly into science’s third great frontier question: How did living things become conscious creatures? Although we like to imagine a world animated by spirits, all of the conscious behavior that we can directly observe is manifested in individual animal bodies. With self-awareness came primordial activities such as mating, hunting, and communicating. Animal behavior is covered in Section VI.
Finally, Section VII reviews contemporaneous developments in the rest of the world: the geophysical planet as well as the plants and animals outside of our lineage. A linear timeline of geological eons and a few chapter highlights is shown below.
- Mountain icon by Memed_Nurrohmad, Pixabay license, https://pixabay.com/illustrations/mountain-icon-sign-design-symbol-1849091/. Egg / sperm icon “reproduction” by Edwin PM, https://thenounproject.com/term/reproduction/1332876/ . “Yellow sponge with green algae” by Luayana, https://www.dreamstime.com/yellow-sponge-green-algae-white-background-yellow-sponge-green-algae-image120195101 . Fish icon by kreatikar, Pixabay license, https://pixabay.com/illustrations/clipart-fish-sea-water-swim-3418189/. All accessed, saved, and archived 9/12/20. ↩
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