Draft Intro: Early Life On Earth

Yep, this is the chapter that ends with “And then the fish walked out of the water onto dry land.”

Luckily for us all, while there was Devonian/Carboniferous seaweed at that point, as well as greenery on land, no cat was around to gobble up the famous four-footed fishy ancestor of so many modern living beings during its world-changing move.

Cats hadn’t evolved yet.

In fact, at the roughly 4-billion-year mark in Earth’s history where we left off in earlier posts, the biological domain that all of today’s macroscopic life belongs to — Eukarya — didn’t even exist.

White cats and evolutionary rules

“Macroscopic” is the opposite of “microscopic”: you can see it without a microscope. (Scientists do get technical and define Eukarya in terms of having a cell nucleus as well as complex internal cellular “stuff” that makes macroscopic life possible.)

The Blob doesn’t count — it’s probably multicellular and definitely carnivorous, unlike single-celled Bacteria and Archaea. (Image: Wikipedia)

After all, when was the last time you saw a bacterium oozing down the street or a fabulous archaean sunning itself at the edge of Yellowstone’s Grand Prismatic Spring and waving at the tourists?

The rules of evolution, broad and simple as they are, won’t allow that at this moment in time and space. Every natural form of life must stay within the borders of its own evolutionary “story.”

Oh, sure, there are occasional accidents, like that time when some type of virus infected an ancestor of Seaweed Cat up there (there’s a wide variety of known viruses and only a few of them make you sick; of course, as we’re seeing now, just one of those can ruin everything).

This shows one of the ways that a mutation can be passed along during reproduction. (Image: Dynamic Science

The virus that colored Seaweed Cat and maybe also your own kitty moved in at just the right point on the ancestor’s double-helix DNA to produce white fur in some offspring. (David et al.)

If it had happened before the African wildcat was domesticated into a house cat, this color mutation wouldn’t have lasted long.

Natural selection would see to that.

Not only does white fur make this little desert predator more obvious to its prey and to larger carnivores, it also lets more sunlight reach the wildcat’s skin, causing overheating, sunburn, and even skin cancer.

White African wildcats wouldn’t survive long enough to pass the mutation to the next generation.

But just the opposite happened when white fur happened in house cats. In a process known as artificial selection, people loved the look, so they collected and bred white cats.

Over time, therefore, artificial selection fixed this mutation in domestic cats.

Nothing lasts forever in a constantly changing world, though.

If having white fur ever becomes harmful again, fewer and fewer white cats will survive long enough to make kittens, and eventually the mutation will disappear.

Evolution is descent with modification, and one of its most basic rules is this: the future belongs to those who show up for it and bring their own building materials.

One consequence of this is our own five fingers and toes on hand and foot, respectively, as we’ll see towards the end of the chapter, if we can survive the second of the “Big Five” mass extinctions.

It’s much less famous than the end-Cretaceous event, but still, paleontologist Gerta Keller describes it as:

…a major thriller, complete with multiple impact events, major magmatic eruptions, climate and sea-level changes, ocean anoxia and multiple extinction events.

That four-footed Devonian/Carboniferous fish wasn’t just going on an adventure. It was a rugged survivor, looking for a better place to live and reproduce!

Featured image: DreamerAchieverNoraTarvus/Shutterstock

Sources: To be listed in the final chapter; specific references in this post include:

David, V. A.; Menotti-Raymond, M.; Wallace, A. C.; Roelke, M.; and others. 2014. Endogenous retrovirus insertion in the KIT oncogene determines white and white spotting in domestic cats. G3: Genes, Genomes, Genetics, 4(10): 1881-1891.

Keller, G. 2005. Impacts, volcanism and mass extinction: random coincidence or cause and effect? Australian Journal of Earth Sciences, 52(4-5): 725-757.

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