Top 10 Evolution Breakthroughs of Life (Part II)

We left off in “The Top 10 Evolution Breakthroughs of Life (Part I)” with two of the biggest evolutionary breakthroughs of all- multi-cellularity and sexual reproduction. Once those two evolutionary breakthroughs hit, it was a whole new game for life! In fact, those events launched breakthrough #6-

6.  The Cambrian Explosion: the rise of predators, prey and body plans- oh my!

Up until about 540 million years ago, multicellular organisms were simple creatures like sponges. These free-form animals have no specialized cells and are about as basic as multicellular life can can be. Then something incredible happened. Suddenly, the number, variety and complexity of multicellular species in the oceans skyrocketed. This burst of new, diverse species is known as the Cambrian Explosion and it happened over a brief period of time. A brief period, in this case, was about 70 million years.

An early arthropod, trilobite, Arctinurus boltoni, from Rochester Shale, New York. Exhibit in the Houston Museum of Natural Science. (Photography was permitted in the museum without restriction.) Photo by Daderot via Wikimedia Commons

Trilobites were among the earliest arthropods. This trilobite fossil of an 8 inch Arctinurus boltoni is from the Rochester Shale, New York, from an exhibit in the Houston Museum of Natural Science. Photo by Daderot via Wikimedia Commons.

The spectrum of species flourishing during the Cambrian Explosion can be seen in the extraordinary fossil record of this period. There’s genomic evidence, however, that the variety of genetic expression had been ramping up for a long time before it showed up in the fossil record.

There were a number of factors contributing to this rise of new species. A major player was a surge in atmospheric oxygen. Prior to the Cambrian Explosion, oxygen was only about 1% of the atmosphere. Remember the culprit of breakthrough #2 in Part I? Well, those cyanobacteria continued to pump out oxygen for the next billion years plus and it accumulated like mad. While atmospheric oxygen rose to a whopping 10%, close to half what it is today, it’s still debated when this happened and how much it contributed to the explosion of new species. Still, the extra oxygen meant animals had more potential energy available to grow larger and more complex.

As the range of animal types grew, some became better hunters and others developed ways to survive being hunted. The predator-prey relationship became a fundamental driver of evolutionary adaptation.

All animals began developing ways of sensing light, which would lead to the evolution of eyes. Some animals adapted to being hunted by evolving hard exoskeletons for protection. These were the first arthropods, the ancestors of all spiders and scorpions, lobsters and centipedes. During this period, arthropods evolved legs, allowing them to scurry about the sea floor more quickly. It was a great adaptation helping them to chase dinner and escape trouble.

Mollusks, too, appeared on the scene with their protective shells that kept predators at bay. These were the first snails and oysters, some of which later lost their external shells to become octopuses and squid.

Some animal species adapted by becoming more efficient predators with flexible internal spines that helped them swim fast and maneuver with great precision. From these first vertebrates evolved fish. From those fish descended all amphibians, reptiles and mammals.

During the Cambrian period, the structural blueprints for animals were developed. There were two broad categories- bilateral symmetry, like sharks and trilobites, and radial symmetry, like starfish and anemones. Within the basic plans, designs for the configuration and organization of internal cavities were developed. It was during this period that the foundational body plans of all future animals evolved.

As diverse, adaptive and successful as many of these animal species were at the time, they lacked one thing that would become an essential gear for nearly every animal to come-

A fossil of one of the first jawed fish, the placoderm from exhibit at the Smithsonian Museum. Photo by James St. John, courtesy of creative commons

A fossil of one of the first jawed fish, the extinct placoderm, from an exhibit at the Smithsonian Museum. Photo by James St. John, courtesy of creative commons

7. JAWS!

Chew on that for a minute.

I bet you haven’t given much thought to the unsung virtues of the humble jaw. But imagine swimming about in the ocean with all the other jawless creatures trying to keep food from getting away while you try to suck it down. It had to be a huge challenge!

Around 380 million years ago, that simple hinged apparatus evolved in fish. Now fish could grab a meal and trap it securely. With some nice dental work added, fish could get a start on digestion by gnawing, cutting and chewing. This made snacking a breeze!

The adaptive advantage of the jaw was enormous. Those without jaws had less ability to take a bite out of the food chain. This adaptation was so successful, it became required gear in nearly every living animal on Earth.

Right about the time jaws evolved, life started feeling emboldened to make a geographic leap that put us where we are today.

8. Land ahoy!

About 44o million years ago, life was ready to take its show on the road. Or more accurately, onto land. This bold move was not for the faint of heart.

If you think about it, living in water is quite a lot easier than living on land. For one thing, you don’t have to fight gravity in the water. The water surrounds and supports your whole body. This makes hanging out a lot less energy-consuming than holding yourself up against gravity on land.

As far as reproduction goes, if you produce enough sperm and ova in the water, you don’t have to be close to your mate to have offspring. You can just float your gametes in their general direction and the currents take care of the rest.

And possibly the worst thing about living on land- it will dry you out!

Among the first plants to move on land are Marchantiophyta, also known as liverworts. Photo by Miguel Pérez.

Among the first plants to move on land were Marchantiophyta, also known as liverworts. Photo by Miguel Pérez.

So, it’s rather strange any living thing would venture out of the sea when life on land is relatively difficult.

But venture they did. Plants were the first to take the daring leap landward.

Plants had always lived closer to the surface of the ocean to get the enough sunlight for photosynthesis. So it makes sense plants prefer the shallower waters along shorelines where sunshine is plentiful. It was only a tiny stretch for them to take root around tide pools and make their way ashore.

Insects were next to make their move. They had already evolved legs, and because it was much safer from predators on land, relocating was a no-brainer. And the air was so oxygen-rich, insects could easily get enough of it with the same lungs they had underwater. They could even absorb oxygen directly through their thin shells. Once insects took the dry road, fish got wise and followed the food chain ashore.

Of course, it wasn’t a cake walk for bigger creatures to follow. Fish not only had to develop lungs but had to grow legs because fins on land just wouldn’t stand up. But it’s fascinating to see that once insects made it to dry land, it didn’t take long in geological time for fish to catch up. It was a speedy 50 million years from the time the first insects made it ashore until the first tetrapods, four-legged former-fish, followed behind. In evolutionary terms, the tetrapods scampered out of the water and chased down dinner in no time at all! These daring tetrapods are the ancestors of all amphibians, reptiles, dinosaurs, birds and mammals.

The tiktaalik is thought to be the first fish to transition from the sea to life on land. Artist's rendering of the tiktaalik based on fossil evidence. Illustration courtesy of U.S. National Science Foundation.

The tiktaalik is thought to be the first tetrapod to transition from the sea to life on land. Illustration courtesy of U.S. National Science Foundation.

But land was no place to start a family. Sexual reproduction in a waterless atmosphere still hadn’t evolved. Animals continued to return to the sea to produce offspring.

Meanwhile, plants were venturing further and further inland, growing giant fern and liverwort forests. More and more oxygen filled the air as plants flourished. The landscape began to change, too, as rocks were cracked by plants’ roots and oxygen worked to corrode just about everything. Fungi followed behind, breaking down dead vegetation and bringing about organic decay. Smaller and smaller rocks combined with decayed organic matter, forming rich soils in which more plants grew and thrived, and where insects could burrow and make homes.

As atmospheric oxygen skyrocketed, insects grew enormous, dominating the land.

It wasn’t until animals could reproduce on dry land that they could leave the oceans behind and venture further inland.  When eggs evolved hard shells which could effectively encase and protect the developing young in a water and nutrient sac, the great leap landward was complete.

But it was how plants evolved next that would completely change life for animals on Earth.

9. Flowering plants: nature’s food court

Do you like cashews? How about chips and salsa? Or do chocolate covered strawberries tickle your fancy? Whatever your favorite snack, chances are it relies heavily on the fruit of flowering plants. Flowers are among the most recent evolutionary breakthroughs, evolving on plants about 150 million years ago. Their emergence bestowed an incredible new source of energy for species of animals all over the world.

Orange minivet sips nectar from the flower of a Thai eucalyptus. Photo By Wan Punkaunkhao.

Orange minivet sips nectar from the flower of a Thai eucalyptus. Photo By Wan Punkaunkhao.

Flowers evolved as fragrant and delicious lures for insects and little critters to move reproductive cells in pollen from one plant to another. But to make and maintain a flower requires a staggering amount of the plant’s energy. The payoff in reproductive success has to be worth the energy expenditure paid up front. And pay off it does! Tiny creatures love the nectar hidden within each flower. Birds and bees get sticky pollen all over themselves and scatter it widely as they fly about. Reproduction using flowers and pollen is a tremendously fruitful endeavor!

Once a flower’s seeds are pollinated, the new offspring grow within the flower, which itself grows into a protective, nutritious, high-energy package- a fruit. The fruit surrounds and nourishes the seeds until they sprout into seedlings. These fruits also happen to be delicious to animals of all kinds. As a result, these flowering plants have become one of the most essesntial sources of energy for animals around the globe.

There are an estimated 250,000 species of flowering plants, more species than any other life form on Earth. They produce zucchinis and barley, gooseberries and cocoa beans, pears and carrots, seagrasses and grapes, walnuts and tea, peaches and wheat. If it’s plant-based and you eat or drink it, it’s from a flowering plant.

When humans moved from hunting and gathering to agrarian societies, it was to cultivate these flowering plants for their fruits. The breaking of bread, raising glasses of wine to friends and loved ones, holiday feasts that mark the seasons of our lives are all centered around the fruit of these flowering organisms. They’re woven into the fabric of our existence as much as any living things in creation.

The fact we are aware of our lives is possibly the greatest evolutionary breakthrough of all-

10. Consciousness: the awareness of existence

Here we are.

Red fox. Photo by RT Images.

Red fox. Photo by RT Images.

We know we’re here.

We’re conscious we exist.

You, gentle reader, know who you are. Wherever you may be, you’re conscious you’re reading these words. Perhaps you even have a sense of this humble writer, typing out this article, endeavoring to share the wonder and miracle of life all around us.

We have evolved from chemical compounds in a lifeless sea to this moment when we recognize and experience this universe from which we are born.

There’s a lot research recently on how to define and measure consciousness. Some postulate consciousness is the degree to which an entity integrates the information it processes.

The laptop I’m writing on is processing information at a staggering clip. But this electronic device cannot begin to integrate informatation with the depth and understanding of a red fox as she surveys her surroundings near the edge of a clearing at dusk.

We humans can and will research and deliberate, form theories and write articles on consciousness for years to come. But for all the brilliance of our consciousness to investigate and discover, to learn, create and reflect, to love, suffer and evolve, perhaps there are some things which cannot be understood through the mind alone.

Perhaps some things are better left a mystery. Perhaps, consciousness is one of them.

Or perhaps, some day soon, in 27 million years or so, we will evolve breakthrough #11 and consciousness will be merely a stepping stone to…

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