A Review of Brain Development

Reaching back almost to the beginning, our brain uses a communication system found in jellyfish, first appearing 600 million years ago. Their nerves and the manner they send signals are similar to ours. Your brain relies heavily on structures found in the animals that preceded us. The first known animal, sponges, appear just before jellyfish. They basically had a more primitive form of the communication system found in jellyfish BUT our brain still uses part of their communication system. How that process evolved between the first multicellular organism and sponges is unknown since fossils are not available.

Worms are the simplest organisms to have a central nervous system, allowing them to exhibit more complex forms of behavior. Insects have a small but remarkable brain which can, for example, permit the cockroach to dart away as soon as it senses the moving air preceding a quickly descending human foot. The insect brain controls crawling, hopping, swimming, flying, burrowing, mating, and you-name-it.

An animal’s information system runs up the spine to the brain. Vertebrates, with that stiff spine, improve the protection of the information system. In early vertebrates, one part of the brain controlled behaviors that had happened again and again. Those automatic responses are sort of like cruise control on a car. A bird flies straight at your head. You do not stop and ponder, “Hmm. Should I duck?” No. Your conscious brain is too slow; a reflex established in antiquity makes you duck.

Science quarrels when the first brain appears, but the more important question is “What does the brain do?” Basically, it signals; it communicates; it directs traffic.

Without using the term “brain,” signaling began with life. From the beginning, cells had a communication system. Without one, how else could the DNA of the first bacteria direct the organism to make a copy of itself and then reproduce by splitting that copy off? Each of those steps, from no-life to life, from bacteria to eukaryotes, eukaryotes to multicellular, multicellular to jellyfish, required cells signaling one another. For sure, the brain was more organized when vertebrates had it at the end of a central nervous system. But communication among cells had to begin with life itself.

The amphibian transition from water to land made a big impact on the brain’s development. By this time, the brain had a midbrain and forebrain where brain functions for hearing and seeing in a higher and drier world sharpened. One part of the brain included responses like dominance and submission. Sudden movements, intimidating objects and brighter light changed visions centers. A possibly threatening or sight or sound causes us to instinctively turn our face and eyes in that direction.

As the finished reptile appears, the brain controls vital functions like heart rate, temperature, breathing, and balance. The brain, at that point, has a brain stem connected to two spheres (called the cerebellum.) This section helps with learning new motor behaviors, such as swinging a golf club.

In addition, most of science agrees that emotional centers also existed in the reptilian brain. Likely members include the instinct to fight or run which might also be called terror or anger. Instincts regarding sexual drives as well as parenting can be found here.

Dinosaurs, birds and mammals all followed reptiles. Each of those began with the same brain structure – the same brain structure as the reptiles. The human brain contains that section (often called reptilian) which still controls involuntary and instinctive behavior. Contrary to the arrogant beliefs of too many humans, the brain did not start over when homo sapiens arrived.

The Evolution of Emotions

Let’s summarize. To begin, in an initial step, the male does not wait until the female eggs were in water. Instead, like those adventurous placoderms before them, the male fertilizes the eggs while they are inside the female. With internal fertilization step complete, all the ingredients needed to create an image of the parents were together inside the female.

Slowly but surely, the reproduction-in-water issue was solved as a remarkable egg, called amniote, evolved. An interesting story. Let’s set the scene:

  • As water sites got further and further apart, the female did not just drop the eggs anywhere; instead, held the eggs inside longer.
  • Amphibians had a kind of tissue surrounding the yolk in the egg. The extra internal time toughened that tissue. Soon, as the embryo grew, the tissue surrounded it, and closed.
  • As that happened, fluids maintaining life stayed inside the now-enclosed tissue.
  • As time passed, the egg shell itself got more and more resilient. Inside the shell, the embryo’s tissue was surrounded by a fluid which collected waste and passed on air to the embryo.
  • That last amphibian step, egg-to-tadpole-to-frog, now happened inside the tissue.

Imagine how much time that took for the mutation-natural selection sequence to cause the change. This happened only because the female did not just jettison eggs and move on; if a site for laying the eggs was not available, the female held them in.

That was the amniotic egg which led to reptiles – animals that did NOT need to stay near water. Now the females laid the eggs on land. Reptiles of today include turtles, crocodiles, lizards, and snakes. Some still need water nearby; others live in the desert. The process that yielded reptiles was complete about 300 million years ago.

As the time clock moves from 1.2 billion years ago to 300 million years ago, from the first appearance of gender to our ancestor reptiles walking on land, how has the evolution of emotions progressed? Start with these sort of background statements.

The most valid animal emotional behavior data is anecdotal. Accurate reports regarding the emotions and behaviors of animals must come from observing, without interruption, animal behavior in their natural environments. Unfortunately, science does not have much respect for such information. Mark Bekoff, arguably the most trusted name in the area of animal emotions, explains that much more clearly and eloquently.

One anecdote, of course, should not lead to a firm decision; two independent reports with similar results tend to be eye-openers, but when report after report after report have a consistent theme, respect is called for. This “emotion” section will lean heavily on information based on observation and anecdotes. Thankfully, there are many scientists pursuing this line of research.

In earliest posts, some kind of special attraction – a mysterious force – seemed to have an impact on all events. In terms of emotion, attraction and cooperation were already seen. Clearly communication existed as well as some behaviors one would associate with a brain. What additional emotion-based research can be found from 1.2 billion to 300 million years ago?

About a half million years ago, about the time sponges appeared, the ancestors of those cherished lobster dinners, crustaceans, appeared.   One crustacean, the hermit crab, actually has no shell of their own. Instead, they find and live in abandoned shells of others. Research searching for hermit crab emotions unearthed two surprising emotional developments this early. First, the hermit crab reacts to pain, and second, the hermit has enough memory to avoid pain. Emotions and memory.

A little later, before the bony fish appeared, those ferocious placoderms provide fossil evidence of internal fertilization. The author of this Scientific American article writes,“The paired pelvic fins in placoderms permitted the males to deposit sperm into the females. This eventually gave rise to the genitalia and legs of tetrapods. And jaws may have originally evolved to help male fish grab a hold of females and stabilize them during mating, only later taking on the role of food pro­cessing. Sex, it seems, really did change everything.” This certainly appears to confirm that force of attraction and reinforce that if some action is rewarding, that action will be sought again and again.

Fish appeared just a little later. In most cases, fish lay eggs to reproduce. The female lays them; male comes by and fertilizes. But this is not impersonal. In most cases, the male is with the female as the eggs laid, immediately fertilizing them. The fish displayed various forms of protecting their young, including building walls. Here the two genders are working together after fertilization, indicating some sort of bond that holds them together. Examples of fairly elaborate nests out of the reach of predators abound. Having the male and female at the same location is not necessary; but many species apparently enjoy (or something) being together at that time. Attraction. Parenting. Being together. Protecting both the born and unborn. Do not believe people who say this did not begin until mammals.

A device that scared fish was inserted in a fish tank, immediately swimming from the feared object to escape. Next time, they were shown a bright light 10 seconds before the scary insertion. Well, over time fish learned to avoid the fearful event by leaving when the light turned on. Then, seven days went by with no light, no fear. On the eighth day, the light turned on. The fish immediately swam to escaped. So, at this point in the evolutionary process, the fish brain demonstrated hearing, fear, learning, and memory.

Bony fish, from which amphibians evolved, are in our evolutionary line. In about 20% of the specie, one of the parents holds the fertilized egg in its mouth, protecting the eggs from danger while waiting for the fry to hatch. That takes about a week. The story continues: In one specie, the father stays with the fry. If danger is near, the father swims to the fry and takes them in his mouth, holding them until danger is gone. What is seen here certainly seems like parenting, already tucked in the brain of some fish.

Here is a new emotion, branching out a little further. Generally, guppy females seek a male with bright orange coloring. However, when a female sees other females mating with a male with non-orange coloring, she will copy that behavior to also seek a male of similar coloring. Culture, seeking to conform to the group, the female is NOT following her own genetic drive but is responding to the behavior of others, as in “Monkey see. Monkey do.” Living in groups creates a whole new set of responses in the brain. Notice that this behavior is connected to parenting (seeking a mate) but has reached beyond parenting.

The female lays eggs; the male fertilizes, sometimes using internal fertilization. Somehow, they most communicate. They appear to choose to stay close. Why? Was it rewarding or maybe just the expectation of a reward? The no-contact technique was more convenient and much safer. That just provides predators a target twice as big! Does it not seem that something else made them seek one another?

The earlier speculative “automatic response” seems to fit here AND seems to be taking on more specific meaning. Something like the “anticipation of satisfaction” certainly seems to be going on. Even now for humans, the anticipation of satisfaction is a common behavior motivation. Catch that: not an actual satisfactory experience but instead being drawn to one another by the expectation of satisfaction.

Remember, these behaviors impact the structure of the DNA and the brain. Genders cooperating to allow internal fertilization certainly seems linked to emotional responses, stretching further the role of expectation of satisfaction in the mating process. Randomness followed by natural selection certainly is true; but from this perspective, it looks like developing emotions are taking a far bigger role in this evolutionary process than science has been willing to accept.

A substantial reproductive change occurred in this step. Usually, the egg (laid in the water) contains a not-yet-fully-developed amphibian. The animal’s DNA , though, then guides the transition of the newly-born to a land-dwelling amphibian.

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?

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 Reign of the Prokaryotes

Here we pick up from Saturday, with the formation of the planets in our solar system and the continents on our planet, Earth. Most of the junk flying around in space had been gobbled up by the Sun, Jupiter, and the rest of the continents. The Earth finally was freed from a constant bombardment of comets and good-sized asteroids. Damaging asteroid strikes did not disappear; they just became much less frequent.

Volcanoes erupted regularly. Between those violent crashes and the volcanoes, the earth’s boiling hot surface included an atmosphere of methane, steam, hydrogen sulfide (the rotten egg smell), and carbon dioxide, in addition to nitrogen and carbon dioxide. No oxygen, though! The earth finally cooled a little, turning the steam into water. Rain poured down for a long time, filling the oceans.

Around four billion years ago, conditions were cruel. The atmosphere and the oceans were a chemical soup. The oceans were green and acidic, the skies orange with high levels of methane, ammonia and carbon dioxide. A complete list of all the ingredients of both the ocean and the atmosphere are not known for certain, but any living plant or animal of today would immediately die if placed in that environment.

Despite these horrific conditions, life appeared. Out of that fiery, dense Big Bang explosion comes the itty-bitty little particles out of which you, your parents, the ground you walk on, the Moon, the stars – everything! – is made. Little bits of that stuff got together just right and out came the first DNA.

Life begins. In the water. Life’s first DNA. That DNA, though, was NOT simple.

Well-preserved bacteria from the era 3.6 to 3.2 billion years ago was found in Western Australia. General agreement for life’s beginning is 3.7 to 3.8 billion years ago.

What arrived was the earth’s simplest form of life. But what is life?

  • A simple explanation: on one hand are living things, plants and animals; on the other hand, inorganic matter.
  • A more precise definition: Living things take in food, grow, and have wastes; they reproduce; and have DNA.

Those first living organisms were single celled. Biology calls them prokaryotic; “bacteria” is easier to remember.

Here is an introduction to that first life form, the prokaryotes. Each organism was surrounded by a thin membrane. Inside the membrane, nutrients moved around, messages were sent, and a variety of other complex tasks carried out. The instructions for all this action were in the DNA. The DNA directions included how to do those things—move, use food for energy, eliminate waste, and reproduce.

Those first living cells were tiny, tiny, tiny. A piece of paper is about one millimeter thick. Those first cells were 1/1000 of a millimeter! Two examples of prokaryotic organisms today are bacteria and green algae.

Those tiny organisms stored essential genetic information coiled up inside. To create this two-for-one step called reproduction, the cell first had to grow to twice its own size. Then it split into two, creating a matched copy of the original. The process was not really that simple but that is an outline.

Reproduction required no external help. The cell was on its own to grow-split-grow-split- … and on and on. Do not scoff at these prokaryotic cells. They are by far Earth’s most consistently successful organism. The reign of the prokaryotes begins and continues for more than two billion years.

Here is a timeline of the beginning of the story from Big Bang to you.

big bang to you

These little bacteria cells had a little tail; they could move about in the water. Today, they exist in plants and animals as well as in the atmosphere. In your body, they help digest food. They also cause you sickness.

The enquiring mind is saying, “How does science know all this stuff? Do they just make it up?” A complete answer would take a book. Next week, a brief explanation!

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