Moving to Land: Amphibians

Amphibians evolved from the lobe-finned fish. Most of this change happened in shallow water. The bottom fins (those little sharp parts that help a fish navigate) were in pairs AND were supported by internal bones.

Environmentally, as the amphibians took charge, conditions were unique. Parts of what is now North America, Europe and Asia were near the equator. They were hot, wet, humid with and were hot, wet and humid with oxygen levels up to 31% (compared to 21% now.) The heat and extra oxygen had much to do with rapid growth, leading to enormous and dense swamps filled with mosses, ferns and giant trees. With six-foot long poisonous centipedes and dragonflies the size of a seagulls, the swamps sound quite unpleasant. However, where this dense vegetation once was, in North America and elsewhere, much later it decayed and became coal.

For amphibians, conditions could not have been more ideal.

The lobe-finned fish lived on plants or smaller fish in that very shallow water. Some was on land. Lobe finned fish to follow it, slowly but surely those four fins strengthened, eventually to be called legs. That transition might have taken 30 or 40 million years. An animal living in water has buoyancy for support; as the lobe-finned fish spent more time out of water, those muscles developed.

The fish had a sort of bony arch through which water flowed. The gills in fish have the capacity to pull oxygen out of the water then merge oxygen with nutrients to provide the fish energy. As more time on land strengthened that strong skeletal structure, those gills became pretty inefficient oxygen providers. That had to change. Eventually, that fish-structure shut down and was lost. As adults, the amphibian has primitive lungs and slimy sort of skin that actually pulls in oxygen through the skin. The gills are gone.

Aha! Your arms and legs have developed.

Water was high; amphibians fit in everywhere. Fossils have been found all over the globe. This event happened at a variety of sites at about the same time. Amphibian fossils have been found on every continent; so clearly they prospered.

Well, those ideal started to change as land masses inched toward each other and climate began to cool. Between 375 to 360 million years ago two extinctions occurred, almost ending this long story. Each lasted for a short (by evolution timing) period of about a quarter million years. But — the party ends. Some think the rapid growth of vegetation increased oxygen levels too much. The temperature dropped sharply. An extinction was hard on water-dwellers; perhaps 75% of all water species became extinct.

When the party ended, though, the amphibians were well underway. They needed water to lay their eggs; but they could also escape to land. The timing of the extinction was fortunate for amphibians. One good thing: those deadly and vicious placoderms ruling the seas became extinct. Most species of insects and plants joined the amphibians in survival.

Building a skeleton to hold up the amphibian on land was a key part of the transition. Surely the process of fins pushing around in shallow water and spending a more and more time in shallower water played a key role in the transition from fins to legs. Artifacts also show this was the start of internal fertilization. The article points that the process of the male holding on to penetrate the female strengthened the legs of both genders. Internal fertilization becomes a key part of the evolutionary process.

Catch that? Internal fertilization started? Just checking.

Amphibians, clearly in the evolutionary line that leads to us, vary in reproductive techniques. Some require penetration, some not. Frogs lay eggs but the male and females are in contact at the time of fertilization.

Amphibian reproductive process is a precursor to the next evolving specie, reptiles. Amphibians leave an egg that produces a fish-like animal which then grows to be an amphibian. For example, tadpoles leave the egg as a fish but eventually transition to frogs. As the newborn gets older, though, the DNA directs a slow transition to adulthood. In this process, the adult amphibian moves from breathing through gills to breathing with primitive lungs and through the skin. The amphibian still needs water nearby to be available but has learned to live for substantial periods on land.

Amphibian fossils suggest the transition from fish to amphibians was complete by about 340 million years ago. Those full-blown amphibians quickly became the big guy on Earth, the dominant specie. If the continents had just stayed separated with a lot of land covered with shallow water, the amphibians would still rule. But the earth underneath them foiled their dominance.

As the earth cooled, those water sites amphibians needed were getting further and further apart. As birth sites diminished, what was a female with eggs to lay going to do?   Next, I will summarize the steps upon which science seems to agree.

The Flexible Backbone Appears

As a very cold period ended, huge glaciers that had formed. Moving slowly, they scraping nutrients from the Earth’s crust to be absorbed by the oceans. This led to a buffet of oxygen-producing algae, providing the oceans with a dramatic increase in living organisms over the next fifty or so million years. Sea levels were very high – maybe a third of mile higher than they are today. Temperatures are mild; the first primitive plants moved onto land, probably a form of the green algae from the water. Over time, that green algae transitioned to very large ferns. Conditions were right for some important steps to take place.

About 600 million years ago, a little animal appeared that acted like a fish but looked like a worm. So what?   Remember the jellyfish with a strangely-arranged nervous system? Well – this little worm-like animal had a feature critical to our later development; a nervous system cord attached to a stiff but flexible backbone.

This little worm-like thing signals the development of an internal skeleton. At this point, no bones yet; instead, up the back, a stiff but flexible bone-like structure which has four flexible bony connections to the fins which will eventually become a bony spine with connections to the four limbs. Equally important, as the stiff part becomes our backbone, this step will carry the spinal cord to the brain. In time, segments of muscle, sort of like a string of pearls, wrap around that stiffened segmented part, providing protection.

Paying attention? Your backbone started to develop with a cord to the brain just like yours.

That worm-like animal evolved into a truly weird one – a fish without a jaw. Jawless fish, making their debut in both in ocean saltwater and freshwater lakes, had a fairly rigid backbone. That internal bone had a sort of upside down arch appearance; a like a couple of McDonalds arches.

The animals were ugly but their senses complex. They could sense sound and pitch and had eyes. Bottom feeders without a jaw, they had a sort of throat underneath them that sucked in water, took out the what was needed, and sent it back out through the gills. Actually, the stiff part was more like cartilage then bone; quite flexible. Some, but not all, scientists view jawless fish as the first vertebrates.

Paying attention? They could hear; they had eyes; and they had a throat.

All around them were bigger, stronger invertebrates who viewed the jawless fish as breakfast, dinner, or snack. In response, over time, these jawless fish developed a tough armored plate on the head. As bottom feeders, armor protected them from attacks from above. In time, that water intake hole moved around to the animal’s front leading to a jaw. These animals, by the way, were TRULY ugly. Say “hello” to the placoderms, not only ugly but nasty. They had an “open wide” mouth, sharp teeth, and were covered with protective armor – sort of an armored medieval warrior with weighting in at about a ton. Placoderms. In one bite one could cut a shark in half! Eventually they went extinct, but attention is needed; they were important contributors to the evolutionary line eventually leading to us. Well, at least humans did not inherit that big heavy plate on their heads.

An animal with a flexible backbone followed the placoderm.   The flexible bone is called cartilage, so (ta-daaaa) they are called the cartilage fish; the modern-day shark is the best-known cartilage fish. A your next visit to an aquarium (or being attacked by a shark) watch how smoothly they move through the water. The flexible backbone allows that movement.

When no one is looking, reach up and hold the divider inside your nose with your thumb and a finger. Move it around. That divider is cartilage, given to you before the cartilage fish spun off from placoderms. Another example: the sports page today reports on an athlete with a cartilage tear in the knee. All of us have cartilage bone junctions. And this will really shock you – but it is true: while you were in your mother’s womb, safe and warm, your earliest bones were cartilage. Then they changed to bones. So the cartilage fish took off on their own but before doing so made some contributions to you.

Besides the cartilage fish, a second group split-off from placoderms had backbones without that flexibility. The bones became hard so (ta-daaaa) they are called “bony” fish. By this point, all science agrees; these are vertebrates, the line that led to amphibians then reptiles and finally mammals and us.

Paying attention? Your bone structure has been added.

So while the cartilage fish went off their merry way, the bony fish line itself split into two parts. One group of bony fish remained in the deeper water.

The first group are what we still call “fish.” Between the oceans and fresh water lakes and rivers, as many as 25,000 fish species from the bony fish line are spread around the globe. For a Minnesota-born fisherman like the author, catching walleyes remains a pinnacle event—almost the reason for living.

The other group sought safety from those huge salt-water animals. The other pathway moved into shallower fresh water, in ponds, bays, and little streams caused by very high water levels on earth. This group needed a place where those huge saltwater predators could not go. This line was called the lobe finned fish because their structure was bones and muscles. Funny name; but this animal is in our direct evolutionary line.

OK, folks. Your ancestors moved out of the salt-water oceans to clean, fresh water. Feeling better?

Increased Complexity Appears

This is about how YOU got here, from that first moment of life in a very unpleasant ocean environment to the homo sapien that you are. Well, me too. It is indeed difficult to compare my body now to two extremely small organisms floating around in the ocean 1.2 billion years ago. But in this section, watch your body start to be put together.

With the availability of two genders, living organisms grew larger and more complex. Fossil remains for this next time period are limited. Why? Those developing organisms were soft. The time had not yet come when shells or bones were in place. Bones and shells will survive a billion years, but soft animals without either are hard to find after that long.   Science has cleverly found sound hints, though.   Most agree rapidly increased complexity was happening. By the time the first evidence is available, those DNA controlling lives probably had more complexity than the computer program that makes Google work.

Science does a good deal of information about the environment of this time. Early in this period, all the earth’s land masses had merged into the supercontinent Rodinia, with the equator going right through the middle. But those land masses started to separate, allowed big waterways to open between two big continental plates. Those ocean currents developed disruptive new routes which, apparently, helped the earth get colder.

Around 750 million years ago, that disruption came to a head. When a lot of water is consumed as ice by the glaciers, oceans get shallower. A substantial part of the ocean freezes to the bottom. Habitats are lost. Earth turned really cold, with ice as much as 2/3 of a mile thick covering most of the surface. Continued life could not be sustained in a substantial part of the oceans, but those little cells continued their march. Things warmed but, oops, around 720 years ago, the earth froze solid again. Life on earth was disrupted but not extinguished.

The first solid evidence of increased complexity, an apparent survivor of the last extinction, was finally found. The animal: a sponge. Some say “the lowly sponge” — not fair for a species that has now lived for more than half a billion years. Scientists believe that, over time, those early sponges greatly impacted the ocean by adding oxygen near the ocean’s bottom. With more oxygen available, new habitats and more life appear in deep water.

Sponges still do live at the ocean bottom, tightly attached to rocks. Their home is a structure with a lot of air-holes that absorb water. They are actually quite similar to the sponge used in kitchen or shower. As water moved in and out of the holes, the sponge absorbed nourishment . No food preparation for sponges; lunch comes to them.

Sponges sound simple but the complexity of their structure had gone well past that of those first bacteria or eukaryotes. One more important observation: although they did not have a nervous system, science recently has found they had the genes that were the precursor of the brain – your brain.

Not too much later, jellyfish appeared – yes, the same ones that can make swimming scary.   Sponges stay at a fixed spot; jellyfish search for food – and are still doing it here on Earth. What kind of more complex subroutines had the jellyfish assembled to survive so effectively?

Water supports them; bones had not yet evolved. Jellyfish are assembled symmetrically. The body plan, viewed from above, looks like an upside-down church bell. Down a center shaft water flows; the jellyfish has a subroutine to pull the food out for nourishment, much like the sponge does. The body, which is mostly water, has one multi-purpose opening where nutrients enters, waste leaves, and eggs go out or sperm comes in for reproduction.

The centralized brain had not yet arrived, but the jellyfish did have a pretty complex nerve net reaching up that central opening.   This nerve net guided where to swim for food – and which way was up or down. The nerve net also provided information about the water’s salt level, necessary because the mistake of swimming out of the salt water meant death for the jellyfish. The jellyfish also had eyes that could see; the signals when through the nerve net. To reproduce, the male releases the sperm and the females swims through it for fertilization.   An interesting cooperative system. And, as some unfortunate beach walkers and swimmers know, jellyfish can sting.

The goal is to show YOU your development process. Those little animals were already doing things we humans do. Think sexual reproduction. Sponges reproduce like hermaphrodites (both genders, one animal), just like the first eukaryote. The process was interesting. The sperm was first sent out into the seawater then drawn back into the animal to fertilize the egg. That process needed some sort of signals, some sort of communication between genders.

For the later-appearing jelly fish, the sperm-making male and egg-making female were separate. To reproduce, the eggs go into the stomach then out the mouth of the female jellyfish, followed by the same process from the male jellyfish. The jellyfish did not yet have a brain, per se, but did have a control system that worked like one. Some sort of cooperation, along with communication, had to exist.

A serious misconception is that emotion is unique only to the human brain. Our predecessors had emotions. An “angry sky” is not really angry; but an angry dog really is. Data that go way, way back confirm emotions can be tracked to the first primitive brains – and maybe even further.

Those first paragraphs describing the reproductive strategies of the sponge and jellyfish are based on scientific research by people who do this sort of thing as their life work. Science knows how they reproduce but an interesting question is, WHY do they reproduce? Science implicitly argues that animals go through the reproductive process so babies can be made. Maybe they are right – but – does it not make more sense that animals go through the reproductive process because of an emotional need or an emotional desire? Were reproduction steps painful, would male and female communicate to cause it to happen again? Of course not!

Cooperation is perhaps related to “being together” or “expectation of satisfaction.” Genders seemed attracted to one another. Cells can send signals; communication is possible. That “mysterious thing” seems to be hovering. Those reductionist pure scientists will not agree, but emotion was already underway for the line that led to you and me.

A Mysterious Force

Time for a pondering and thinking and speculating break. Since the appearance of gender seems so critical to that which followed, out of curiosity, suppose those critical first six steps are viewed backwards. To begin, though, remember the following.

Science has pretty much agreed on this: each little step depends on and draws from that which existed before. Close your eyes and try to picture these critical steps – from Big Bang to the appearance of separate genders.

Right after Big Bang, a mysterious force caused matter to seek other matter, thereby stopping the momentum to fly away in straight lines forever. Science calls it gravitational attraction.

Attraction. Keep that word in mind as the next step appears.

Life begins. Little, bitty single cells. Reproduce by making a copy of self and splitting into two. But a Nobel Prize was awarded to Max Delbruck in 1969 about the “…replication mechanisms in viruses.” An earlier Scientific American article by him has this summary: “Some fascinating experiments demonstrated that the tiny organisms which prey on bacteria employ a primitive kind of sexual reproduction.”

In other words, the makings of gender were there. About a billion years later they would separate but they were there — right from the beginning!

Look back. “Each step depends on and draws from that which existed before.” The makings of gender must have been in the noxious water from which life first appeared. Those “makings” would be different from the inorganic material around them; is that an attraction the put together the first DNA leading to first life?

Just pondering here.

In one of these new-fangled complex cells, over perhaps a half billion years, the material that made one gender separated from the material that made the other gender.

Two things to remember: The material from which the two genders was formed came from events that happened earlier. Some sort of force or pressure caused the material to separate from one another. Whatever was necessary to cause genders to separate after a long time in a single cell must have been drawn from those first complex cells.

Those first complex cells were built from material in single-celled organisms preceding them. In the other direction, gender differentiation was drawn from material in those first complex cells. Is that force or pressure causing gender separation part of this package? Did, by any chance, that unknown force have any connection to the merging of the two single-celled organism?

Life begins. Look back. The material appeared in first life had to contain what those two single-celled organisms needed to make that first complex cell. Look forward: First life had to separate from inorganic matter. That DNA assembled in water had to have material from which gender was assembled.

Once again there is a separation. Was that mysterious force separating genders involved in sorting the material needed for first life from inorganic matter?

Right after the Big Bang, a mysterious force caused matter to seek other matter, thereby stopping the momentum to fly away in straight lines forever. Science calls it gravitational attraction.

Think about it. “Attraction” is the key connecting word here, start to finish – at every step. Is that mysterious force already at work?

For this mysterious force to have that kind of impact, cells had to somehow communicate with one another. How could this mysterious force somehow have a way to communicate to guide cells to these dramatic changes?

Cells can communicate. Those very, very first DNA could not have done its job without some kind of electrical burst. Imagining a communication system is hard to accept – but then it is hard to imagine them having a complex DNA as well. The DNA guided each step; communication had to be there.

 

A snowball is flying at your face; you duck, instinctively, without thought. A little hummingbird can sing and fly, do a complex dance to attract a mate, build a nest, find food, and a lot more. Information about how and when to move the wings is signaled from the little bird’s brain. Communication. For DNA to work, a communication system had to exist. Is that how the material defining male and female slowly guided cells together in that chemical soup? Could there be a connection between matter seeking other matter and the elements of that soup sorting organic from inorganic through some kind of communication?

The key here: cells can signal one another; signals are sent from one part to the other. The idea of a mysterious force is not far-fetched.

Taking this approach, life’s beginning is just one stop in a continuous process. Life’s emergence is not a random event but just one stop in the transition from Big Bang to gender. Out of nothing, randomly, comes gender? No. Contemplation time seems to suggest a series of connected events, six events each unique in their own way. After all, each step depended on that which had already happened.

Science has the development of emotions and the brain starting much later than this. But that mysterious attraction certainly sounds like a prelude to emotions. If so, it is not only an emotion but the key emotion. And the fact that cells could communicate certainly sounds like the precursor of a brain which science declares begins much later.

The Mystery of Gender

Two types of single-celled bacteria merge to make a more complex cell.

After all, those bacteria were extremely efficient in passing along their genes to future generations. In their billion years or so of the Reign of the Prokaryotes, they had spread everywhere the oceans took them and even up onto some land masses. If the name of the game is successful reproduction, it sure looks like the prokaryotes had the upper hand. Nothing was broken; why fix it?

In the dog-eat-dog evolution that most people connect with Darwin’s theory, why would two successful and independent bacteria species give up their independence by cooperating to produce a new cell? Why not just keep reproducing their own stuff?

The cause is not explained by Darwin’s mutation followed by natural selection. Teamwork is the agreed-upon cause. Evidence shows that the new eukaryotic cell is clearly related to the two single-celled organisms. Maybe one species used the other as meal, but whatever caused it, symbiosis is the term used for a merger like this – an event that happens when one organism needed something the other organism had. At this time, the environment may be been nearing a Snowball Earth time. Maybe the two organisms needed this merger to stay alive.

What caused the two genders to separate within one of those more complex cells?

Science can tell you everything you want to know about inheritance of traits. But if there exists a scientific answer to the question, “How come the material making up the two genders separated in that cell?”, this researcher’s efforts failed to find it. However, one can find a lengthy list of why this SHOULD NOT have happened. Reasons:

  • Sexual reproduction makes the process less efficient. The result: it burns up more energy than just splitting into two new cells.
  • Look at the complication this adds to reproduction. Bacteria just split cell – and that’s it! The more complicated way: that egg floating around needs a mate.
  • That mates uses energy to get there. That energy might be better spent just splitting like the prokaryotes did.
  • Connecting with a mate brings in the idea of competition. Over time, females invest a lot of energy into being the most attractive so a male is drawn to them.
  • Two genders exist but only one reproduces. The other half does not reproduce.

My statistical side is screaming at me, “No. Genders were not necessary. The deck was somehow stacked to help guide that sorting!” What caused the two genders to become separate from one another?

“The deck was stacked.” How?  Science has pretty much agreed on this: each little step depends on and draws from that which existed before. Keep that mind through this review of the steps to here.

 

Student Performance Diagnostics

How does Foundation for Excellence lead to annual student performance growth?

Figure 1

Working individually after group instruction, fast-learning and/or highly motivated students will demonstrate mastery more quickly.  With 90% mastery before leaving a level, the percent of students reaching the upper level will increase each year.

 

In the usual group instruction model, error baggage will inevitably accumulate over time. Only those who begin at the very top will stay there.

Figure 2With 90% mastery required (instead of the usual 60-65%) AND an accumulation of more students in PR95-99, median scores can be expected to increase each year.

Question: How can the Foundation for Excellence get 90% mastery before a student can move on?

Answer: The task was not simple.

Distribution of Diagnostics by Level and Curriculum area:

Diagnostics Distribution Chart

No error baggage will escape.

If that student leaves group instruction with error baggage, each error WILL be identified and corrected.

Now go back to first page: “an objectives-driven program.” What are the objectives? We’ll get into that on the next Foundation for Excellence post.

Caused by randomness?

Fossil evidence of this trip from single-celled to multicellular is scarce. Those first organisms were soft; a billion years or so later they do not leave any marks. However, scientists, working in their labs, have done a pretty good job of recreating this last transition. The evidence indicates the trip from single-celled to multicellular was a step-by-step process, a convergence, and not one big dramatic change.

In the absence of fossils, estimates of when this last step happened conflict. Based on evidence available suggest multicellular appeared about 1.5 billion years ago, or 2.2 billion years after first life began. However, the appearance of two genders will indeed speed things up.

Now, a quick review of those “six colossal and scientifically explained events.”

six-events

What does science say about those six steps?

Start with the Big Bang.

An inquisitive mind is saying, “What caused the Big Bang?” Science has no response to the cause. Well, “What was there before the Big Bang?”   Some say “nothing.” Others believe the Big Bang is part of an endless cycle, that mass and matter existed previously, slowly crushed down to one point. Then Big Bang 2, and the cycle goes around again – and again – and again — throughout infinity.

But wait: the cycle cannot exist unless it started at some time. So the question remains, “What caused Big Bang?”

What has science to say about gravitational attraction?

Every piece of mass in the universe is attracted to every other piece of mass in the universe. Gravity appeared immediately with Big Bang. What caused that?

Einstein said space and time curved sort of like the capital letter “U.” One side was heavier so the lighter objects on the other side fell toward it. To scientists, that makes sense in the big, big picture but does not explain why the dropped pencil was pulled toward the desk.

Much research effort has been directed toward a little particle called graviton, theorized to be the cause gravitation force. The search to find one has not been successful. It seems the world of gravity and the world of subatomic particles (electron, neutron, and so forth) will live side and never fit into one unified theory.

Newton gave us the equation but not the cause. In his book, Lloyd describes this a “a mysterious thing” and “force of gravity, a kind of invisible glue that makes everything in the universe want to stick together.”

So what caused life to begin?

In the 1950s, two scientists did produce amino acids, the building block for life, from gases which were available at life’s beginning. This caused a good deal of excitement, but no one has been able to make those amino acids produce a cell machine that reproduced itself. Compared to living animals today, the prokaryotes DNA is simple; but compared to no DNA at all, the prokaryotes are very, very complex. Somehow, organic grew from inorganic. That step was not in any way simple!

Trust me, scientists have tried and tried to repeat the process in the lab. But by 2001, a leading science journal reported, “Scientists are far from creating life in the laboratory, and it may never be possible to prove exactly what chemical transformations gave rise to life.” No matter how hard chemists, biologists, and molecular biologists tried, they could not replicate those last steps to life.

Some scientists speculated that life was carried to earth on a comet. Proof of that claim is unlikely. In 2009, Scientific American reported, “Scientists are now aiming at creating fully self-replicating artificial organisms.” Notice this article did not use the word “life.” The target has gone from “life” to “an artificial organism.” A year later, another scientist wrote, “It is virtually impossible to imagine how a cell’s machines could have formed spontaneously as life arose about 3.8 billion years ago.”

One of religion’s sharpest critics (Dawkins) agreed, writing, “The origin of life only had to happen once. We can therefore allow it to have been an extremely improbable event, many orders of magnitude more improbable than most people realize.” In other words, to a person with a Ph.D. in statistics, he is saying, “This event was not caused by randomness.” Hmm.

From one cell to many: Eukaryotes

At first, one cell included both gametes; a cell like that is called hermaphroditic, which means both the two genders still reside in the same membrane. They reproduced with hermaphroditic cells breeding with another. But before long, the two genders separated. One gender produced the egg and the other the produced sperm, just as humans do today. Soon the hermaphroditic cells pretty much disappeared and the single-sex cells dominated. Logic suggests a lot of reasons why that should not have happened:

  • Males compete with one another for the most desirable female with which to mate. Sometimes these competitions get pretty brutal.
  • The process the eukaryote goes through to reproduce is considerably more lengthy in time than is the prokaryotes process. Waste some time, fall behind.
  • And finally, the product of the reproductive process includes males and females. Males cannot reproduce. Thus the system is only half as effective as before.

Despite these, the event happened—and had it not happened, Earth would still have no living things but the single-celled prokaryotes.

The rate of evolutionary progress with the appearance of sexual reproduction increased dramatically. Looking backwards, sexual reproduction was a critical step leading to us. Period. Too many argue, “Well, it had to happen or we would not be here!” That statement assumes that the potential benefits are known by natural selection in advance. But the Darwinian process is randomness; pure, unadulterated randomness. Forecasting the future is not part of the process.

So two prokaryotes species game up their identity to make the eukaryotes but the eukaryotes were not gracious all. Their DNA called for ingesting food. To those new, bigger cells, bacteria were food. In fact, after a while a hole in the greedy eukaryotes membrane appeared, allowing the eukaryotes to swim along ingesting the bacteria. That hole eventually became our mouths. But the gobbling eukaryote was still a single cell.

In time, those special-duty single cells began to work together, sort of like “You make the soil, I’ll get the seeds, Al can plant them, and Louise will pick them.” They attached themselves to one another. But they retained their own DNA. Bigger cells had a competitive advantage. The problem: a single cell had a size limit.

Eventually, in order to get bigger, those the cooperating single-celled gave up their independence, in a one sense, to stay alive. They merged together, and became multicellular. The individual direction-centers were merged into one more complex DNA.

Multicellular means that now a lot of single cells, each with special functions, work together. As life becomes more complicated, so does the DNA at each step of the way. The DNA, remember, is the main library where all the directions are kept. As the organism becomes more complex, progress is maintained in the DNA.

Eukaryotes are the new kid on the block. So what, you say? Plants, fungi and animals will evolve from the new kid on the block. “Animals” include YOU!

timeline

Fossil evidence of this trip from single-celled to multicellular is scarce. Those first organisms were soft; a billion years or so later they do not leave any marks. However, scientists, working in their labs, have done a pretty good job of recreating this last transition. The evidence indicates the trip from single-celled to multicellular was a step-by-step process, a convergence, and not one big dramatic change.

In the absence of fossils, estimates of when this last step happened conflict. Based on evidence available suggest multicellular life appeared about 1.5 billion years ago, or 2.2 billion years after first life began. However, the appearance of two genders will indeed speed things up.

The Beginning of Gender

During the Reign of the Prokaryotes, the continental plates of today, estimated to be about 20 miles thick, were pretty much in place. The location and configuration of those plates can make a huge impact on environment. Earth today has these distinctly separated land masses: the Americas, with one fairly narrow connection from North to South; Africa and Eurasia, again with reasonably narrow connection from Eurasia to Africa. Australia and the South Pole are separate.

Over time, more complex life forms continued to develop, BUT they had to live through some truly dramatic changes on earth. Here are just a few examples.

The land masses move – very slowly, but they move. When one drifts into another one, serious damage can be done. Some land is pushed down; some land is pushed up, making mountains. This is how all of today’s mountains were formed.

At times, all the land masses are connected. One big continent. A supercontinent! One big ocean. One big continent. When a supercontinent is formed, different currents disappeared, which also caused prevailing winds to change. When ocean currents change, rapid cooling or rapid warm up can be triggered.

If all land is massed at one location, the land near the center is no longer impacted by ocean temperature. The ocean is too far away. So the center of this huge land mass can display huge variations in temperature and rainfall.

When a supercontinent begins to break up, the oceans can once again flow between them. New ocean currents form. Sometimes they make the land around them warmer; sometimes colder. Life trying to survive must change enough to survive.

At times, huge land masses would drift over the South Pole. Huge glaciers build up. Impact: those glacier use up a lot of water from oceans. Water levels fall. Continent gets colder. Glaciers form that are 2/3 of a mile thick. When most of the planet freezes, science calls it a Snowball Earth. These have happened more than once. When this happens, habitats disappear; life forms at that time struggle to survive.

Back to first life, the little bacteria. When they had appeared, no competition existed – they could reproduce as fast as they wanted to. And they did!

How? To start with, those first prokaryote cells had a membrane with its DNA (genetic structure) floating around in the center. One cell can reproduce without any outside help. A cell made a copy of its genetic structure, splits in two, and eureka, two cells for the price of one, each with the original DNA. Acting alone, they can reproduce quickly — some as fast as every fifteen minutes! Compare that to your mother’s waiting time of nine months. No wonder they spread from their birthplace all around the world.

Those bacteria, remember, ruled the earth for over a billion years, and during that time mutations led to a whole variety of bacteria species. Instead of swimming around independently, they merged together. Green algae, still all over the earth, is just one of those clusters of bacteria.

So how and why did new organisms appear? Near the end of the Reign of the Prokaryotes, two of those clusters – each cluster representing a different species – joined together. Why? Well, it might have been due to a suddenly tough environment – maybe a Snowball Earth.  Not sure. Did one want to eat the other for dinner? Not sure. Scientists are sure, though, that one cluster sort of dug itself into the other.

So, one species was living inside the other. Remember the definition of life: The need to have food, use those nutrients for energy and growth, and then get rid of unused waste? As independent prokaryotes, they reproduced quickly, dumping their waste. Sounds pretty unpleasant, doesn’t it? Living in each other’s waste?

In any event, it turns out the invader had something the host needed AND the host had something the invader needed. Thus, the merger was, in a sense, a sign of cooperation. Little by little, they became more dependent. Soon, the invader species was there for good. Two species became one. Sounds romantic, eh?

“For good” meant neither one of the original two species was an independent organism, with their own special DNA, like they had been before. Each had sacrificed its independence to create a brand new organism – an organism with its own DNA. And the new organism was much, much more complex than any of the bacteria species. The new organism’s name: eukaryote, pronounced u-car’-e-oat, with emphasis on the car.

Remember when the prokaryotes avoided extinction? That process that saved them was Darwin’s random mutation and natural selection model. However, changing two different species of bacteria into to a new complex membrane with its own DNA is really quite different. Mutation then natural selection does not work here. Science needs another answer.

Here is how science sees this step happening. Those first bacteria cells had their DNA floating around in the membrane. Think of DNA as chief record-keeper. All those DNA records are in a sort of file; each file controls a behavior. Those various files are called chromosomes. Each chromosome was a set of directions for swimming or providing energy or getting rid of waste and so forth.

Careful studies can see pretty solid evidence that the parts of the new, more complex eukaryote came from the structure of the two bacteria species from which they formed. Scientists can see remnants of some of those “files” (chromosomes) that were in the bacteria which are now in the eukaryote.

This important pattern continues: that which is new builds out of that which already exists.

None of those files can function without available energy to do the task. For the more complex cell, nutrients taken in merge with oxygen to provide that energy. This is true of all animals. A very similar cell merger yielded a eukaryote that used carbon dioxide and sunlight to make energy in a different manner. That merger is called plants. So the distinction between plants and animals followed parallel paths, not necessarily at the same place or time. The difference between plants and animals is in how they make energy.

A key file inside the membrane controlled reproduction. The first step in the reproduction of eukaryotes mimicked that of bacteria.

  • First the cell made an exact copy of itself.
  • Then that cell would split, making two cells exactly alike.

Again: eukaryotes building on what the prokaryotes had already done. But after that, the process becomes much more complex. Science believes these are the steps:

  • The DNA “doubled up” as it is today – with two strands (the earlier bacteria had but one strand.) Perhaps the two built off the single-strand DNA from each bacteria.
  • Then, by going through a complicated series of steps confirmed by science, two new cells resulted.
  • The two cells were called “gametes.” The brand new gamete cell is a sex cell.
  • The result of a complicated series of steps was that one gamete represented one gender and the second gamete represented the other gender.
  • Only the sex cell part of the doubled-up strands was used for the new DNA used in reproduction.
  • Science named the smaller, quicker gamete “male” and the bigger, slower-moving gamete female.

Exactly when this happened – perhaps a billion years after the first single-celled eukaryotes – two genders had appear. The author’s first thought was the lyrics of a song: “Then peace will guide the planets, and love will steer the stars.”

Wow! Two billion years of life had passed without any mention of male and female. Two species of bacteria got together and, after some time, merged into a brand new, more complicated cell. After a while, that more complicated cell organizes such that sex cells appear that define gender for the first time. Getting to this point took perhaps a billion years after the first eukaryote cell – a billion years for that incredibly important gender identification step to appear!

Anyway, the story has a few more steps. On Friday, I’ll explain.

Next post: Gametes and more

Previous post: Enter Oxygen