Homo Sapiens et al
Lucky us, we are of the species Homo sapiens, the pinnacle of human evolution at the moment. We are most closely related to the great apes — chimps, gorillas, and orangutans — but did not evolve directly from them. Most likely, we evolved from Homo heidelbergensis, an earlier species of human from about 300,000 years ago.
So, you ask, when did the first humans evolve from the apes? Between two million and six million years ago. Of the species of humans that have come and gone since, experts have identified more than 20 so far, the exact number depending on how you define human. The Smithsonian's list of them is here.
When our species appeared, at least eight of those now-extinct species of humans were still around. We almost certainly interacted with them and likely interbred.
If the planet survives, a new species of human ultimately will arise. And we will die out, and their scientists will be studying us.
Speed and Distance
In a vacuum, light travels 186,282 miles per second. Thus, in one minute, light travels about 11 million miles; in one hour, about 670 million miles; in one 24-hour day, 16 billion miles; in one 30-day month, 483 billion miles; and in one 365-day year — a light year — 5.9 trillion miles.
As you know, distance in astronomical terms is measured in light years, which is useful and practical, up to a point. Proxima Centauri, the closest star to the sun, is 4.24 light years away. The center of the Milky Way Galaxy is 26,000 light years away. Andromeda, the closest galaxy to ours, is 2.5 million light years away.
Astronomers say the edge of the observable universe is 42 billion light years away. So, how many miles is that? 5.9 trillion multiplied by 42 billion is… a boatload of miles.
The Thagomizer
Stegosaurus was an herbivorous Jurassic-era dinosaur notable for its tiny head, armored plates along its back, and spiked tail. The distinctive spikes, probably used to defend against predators, had no specific name until cartoonist Gary Larson invented one in 1982.
Almost immediately, the term thagomizer was embraced in scientific circles and accepted as a proper anatomical term for the array of spikes. Today, the word is used freely by the Smithsonian, the BBC, the National Park Service, etc. and is used regularly in technical papers.
To be clear, the dinosaurs died out 65 million years before humans appeared. But in 2010, computer studies of the damage possible when a Stegosaurus swung its tail confirmed that Thag Simmons would have been a goner.
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