THE FIRST PLANTS AND ANIMALS
‘One exercises justice or injustice to plants and animals as well.
Plants and animals also have a right to unfolding and self-realization.
They have the right to live.’
Arne Naess
Plants and animals also have a right to unfolding and self-realization.
They have the right to live.’
Arne Naess
Around 550 million years ago, after a 200-million-year period when ice covered a large proportion of Earth’s surface (an Ice Age), multi-celled beings, still in the water but now in significantly different shapes and sizes, took a huge step. They diverged into what biologists call the kingdoms of plants (technically still algae at this time) and animals.
Experts don’t know how it happened, but early tube-like polyps provide examples of transitional species because, judging from their direct descendants today, they must have behaved like plants at one stage and animals at a later stage.
While immature these descendants attach their bottom end to a rock or another polyp, and at their top end catch food by means of a flowery circle of tentacles around their mouth.
Then at maturity they produce cloned offspring in the form of buds. In species like anemones and corals these stay attached to the parent. But in species like jellyfish the buds break off, hang their tentacles down, and drift until male and female cells unite to make flatter, flabby offspring that can move purposefully. These then swim off in search of a rock or another polyp that they can settle on, and the cycle begins again.
Experts also don’t know how kingdoms branched into the progressively narrower classifications used to structure what we call The Tree of Life, based on kingdoms, phyla (or divisions), classes, orders, families, genera, species and races. (You may remember this as “Kings Play Chess On Fat Green Stools".)
However there is growing evidence that great diversifications happen quickly in evolution - in response to a crisis, or tipping point, of some kind.
The main differences between the plant and animal kingdoms are found in their cell structure and their sources of energy.
Plants and algae have hard-walled cells containing chloroplasts that make food by photosynthesis, and they also gain several trace nutrients by absorbing various minerals dissolved in water. Animals on the other hand have soft-walled cells with no chloroplasts to make food, and so their energy comes from plants. They also need the oxygen released by photosynthesis in order to breathe. Therefore plants are absolutely essential for them.
But neither animals nor plants can live without microbes. Oxygen-avoiding (anaerobic) microbes live in an animal’s stomach, breaking up what it eats into a form that it can absorb or excrete. And oxygen-tolerant (aerobic) microbes break up the waste that an animal excretes into water-soluble elements that plants can absorb.
So back in our story, life on Earth now had a way of being that involved interdependence among very diverse beings. Their vital needs were inextricably intertwined.
From this point microbes, plants and animals have all been integral parts of a complex local web of life, evolving together as they compete for available resources and avoid conflict by settling into separate niches.
By concentrating on certain locations or on certain kinds of food they learn to adjust their boundaries. By feeding on weaker individuals, new growth and infants they restrict but also assist each other’s progress, ensuring that the fittest members of each plant and animal species are the most likely to live to maturity and then reproduce.
Today’s scientists see each being as having a chance to thrive within the environment that it is helping to create. So their focus is on co-evolution rather than evolution, ecosystems rather than habitat, and ecology rather than biology. In this approach, since each species has evolved by learning through feedback loops how far its self-interest extends in its ecosystem, no one way of being can be seen as dominant.
Of course as yet in our story there were only aquatic ecosystems. But they ranged from surface areas, where most animals ate living algae, to ocean floor or riverbed areas, where most animals scavenged for algal or animal remains in sandy sediments built up by microbes that separated minerals out from the water.
And we have at last entered the realm of organisms visible to the naked human eye. From now on we will concentrate on their development.
As plant and animal populations both exploded, another evolutionary step occurred.
A few animals began preying on their fellows rather than eating plants or scavenging. An animal species’ way of being from now on would involve survival by eating plants and/or other animals.
And since animal-eaters have to pursue, catch and then kill for their food, and prey animals have to avoid predators and/or fight for their life, they all need more creative attentiveness and more complex organization than plants do.
So nerve and muscle tissues developed, with the nerves sensing an internal or external signal, and the muscles responding appropriately. At first this involved an automatic (or instinctive) pattern of behaviour. In response to a "possible food" signal an animal moved towards it (the forerunner of pleasure), and in response to a "possible danger of becoming food" signal it moved away (the forerunner of pain). But eventually it would lead to active awareness of sensation (sometimes called sentience).
Now many plants and animals were also growing larger as they competed for an ecological niche. A few were beginning to use colour to attract or warn others, while others were making use of the excess calcium that they took in from the water.
Thus on the ocean floor some polyps were using excess calcium to make protective shelters. With the help of microbes that deposited carbon the shelters slowly built up as coral reefs, which today are one of Earth’s most productive ecosystems. One of them (Queensland’s Great Barrier Reef) is the biggest structure that animals, including humans, have ever made.
In other animals the instruction to excrete calcium somehow changed to an instruction to make a protective sheath on their soft body. When an exterior skeleton and jointed legs eventually formed and the animal survived and reproduced successfully, this led to a new division (or phylum) of animals: arthropods. They included the now extinct trilobites.
All these animals had to shed their old skin before they could grow larger and make a new exo-skeleton. And this is still true for their descendants today. But a few soft animals in another animal division: mollusks, were creating either coiled or cone-shaped shells of calcium that grew with them.
To enhance their attentiveness even further some scavengers developed spots sensitive to light (forerunners of eyes), and some swimmers became sensitive to vibrations through their gills (forerunners of ears). To enhance responsiveness, particularly in the challenging ecosystem near the surface, some developed a central nervous system: another fractal arrangement that picked up signals from various nerves and relayed them to a central processing organ, the brain.
This led to the division of chordates, and then over time a few chordates started depositing calcium inside their bodies to protect their brains and central nervous systems (skulls and backbones). This gave rise to vertebrates, some of which later used calcium to develop jaws for grasping prey more easily.
The asymmetry of immobile sponges compared with the radial symmetry of slow-drifting jellyfish and then the bilateral symmetry of swiftly swimming fish demonstrates how these changes enhanced evolution. In each case the changes helped the animals concerned to find a more secure niche in the now teeming web of life.
And within that web of life microscopic organisms were also diversifying, using silica rather than calcium to make structural improvements. Today this diversity is seen in the micro-plankton that include beautiful diatoms near the surface of the ocean.
And so in several aquatic ecosystems within Earth’s salt waters and fresh waters, plants and animals developed extremely diverse ways of living, including different kinds of asexual and sexual reproduction.
But male and female animal cells were still ejected into the water en masse, with only some managing to pair off. Each resulting egg contained instructions so that the hatchling could develop independently of its parents – but only if it was one of the few that survived infancy. This method of generational transfer is still widespread in aquatic ecosystems today.
Meanwhile tectonic plate movement, driven by activity deep within our planet, had created the huge supercontinent Gondwana and several lesser landmasses. And there were some cosmic players beyond Earth that hadn’t yet made their presence felt.
Experts don’t know how it happened, but early tube-like polyps provide examples of transitional species because, judging from their direct descendants today, they must have behaved like plants at one stage and animals at a later stage.
While immature these descendants attach their bottom end to a rock or another polyp, and at their top end catch food by means of a flowery circle of tentacles around their mouth.
Then at maturity they produce cloned offspring in the form of buds. In species like anemones and corals these stay attached to the parent. But in species like jellyfish the buds break off, hang their tentacles down, and drift until male and female cells unite to make flatter, flabby offspring that can move purposefully. These then swim off in search of a rock or another polyp that they can settle on, and the cycle begins again.
Experts also don’t know how kingdoms branched into the progressively narrower classifications used to structure what we call The Tree of Life, based on kingdoms, phyla (or divisions), classes, orders, families, genera, species and races. (You may remember this as “Kings Play Chess On Fat Green Stools".)
However there is growing evidence that great diversifications happen quickly in evolution - in response to a crisis, or tipping point, of some kind.
The main differences between the plant and animal kingdoms are found in their cell structure and their sources of energy.
Plants and algae have hard-walled cells containing chloroplasts that make food by photosynthesis, and they also gain several trace nutrients by absorbing various minerals dissolved in water. Animals on the other hand have soft-walled cells with no chloroplasts to make food, and so their energy comes from plants. They also need the oxygen released by photosynthesis in order to breathe. Therefore plants are absolutely essential for them.
But neither animals nor plants can live without microbes. Oxygen-avoiding (anaerobic) microbes live in an animal’s stomach, breaking up what it eats into a form that it can absorb or excrete. And oxygen-tolerant (aerobic) microbes break up the waste that an animal excretes into water-soluble elements that plants can absorb.
So back in our story, life on Earth now had a way of being that involved interdependence among very diverse beings. Their vital needs were inextricably intertwined.
From this point microbes, plants and animals have all been integral parts of a complex local web of life, evolving together as they compete for available resources and avoid conflict by settling into separate niches.
By concentrating on certain locations or on certain kinds of food they learn to adjust their boundaries. By feeding on weaker individuals, new growth and infants they restrict but also assist each other’s progress, ensuring that the fittest members of each plant and animal species are the most likely to live to maturity and then reproduce.
Today’s scientists see each being as having a chance to thrive within the environment that it is helping to create. So their focus is on co-evolution rather than evolution, ecosystems rather than habitat, and ecology rather than biology. In this approach, since each species has evolved by learning through feedback loops how far its self-interest extends in its ecosystem, no one way of being can be seen as dominant.
Of course as yet in our story there were only aquatic ecosystems. But they ranged from surface areas, where most animals ate living algae, to ocean floor or riverbed areas, where most animals scavenged for algal or animal remains in sandy sediments built up by microbes that separated minerals out from the water.
And we have at last entered the realm of organisms visible to the naked human eye. From now on we will concentrate on their development.
As plant and animal populations both exploded, another evolutionary step occurred.
A few animals began preying on their fellows rather than eating plants or scavenging. An animal species’ way of being from now on would involve survival by eating plants and/or other animals.
And since animal-eaters have to pursue, catch and then kill for their food, and prey animals have to avoid predators and/or fight for their life, they all need more creative attentiveness and more complex organization than plants do.
So nerve and muscle tissues developed, with the nerves sensing an internal or external signal, and the muscles responding appropriately. At first this involved an automatic (or instinctive) pattern of behaviour. In response to a "possible food" signal an animal moved towards it (the forerunner of pleasure), and in response to a "possible danger of becoming food" signal it moved away (the forerunner of pain). But eventually it would lead to active awareness of sensation (sometimes called sentience).
Now many plants and animals were also growing larger as they competed for an ecological niche. A few were beginning to use colour to attract or warn others, while others were making use of the excess calcium that they took in from the water.
Thus on the ocean floor some polyps were using excess calcium to make protective shelters. With the help of microbes that deposited carbon the shelters slowly built up as coral reefs, which today are one of Earth’s most productive ecosystems. One of them (Queensland’s Great Barrier Reef) is the biggest structure that animals, including humans, have ever made.
In other animals the instruction to excrete calcium somehow changed to an instruction to make a protective sheath on their soft body. When an exterior skeleton and jointed legs eventually formed and the animal survived and reproduced successfully, this led to a new division (or phylum) of animals: arthropods. They included the now extinct trilobites.
All these animals had to shed their old skin before they could grow larger and make a new exo-skeleton. And this is still true for their descendants today. But a few soft animals in another animal division: mollusks, were creating either coiled or cone-shaped shells of calcium that grew with them.
To enhance their attentiveness even further some scavengers developed spots sensitive to light (forerunners of eyes), and some swimmers became sensitive to vibrations through their gills (forerunners of ears). To enhance responsiveness, particularly in the challenging ecosystem near the surface, some developed a central nervous system: another fractal arrangement that picked up signals from various nerves and relayed them to a central processing organ, the brain.
This led to the division of chordates, and then over time a few chordates started depositing calcium inside their bodies to protect their brains and central nervous systems (skulls and backbones). This gave rise to vertebrates, some of which later used calcium to develop jaws for grasping prey more easily.
The asymmetry of immobile sponges compared with the radial symmetry of slow-drifting jellyfish and then the bilateral symmetry of swiftly swimming fish demonstrates how these changes enhanced evolution. In each case the changes helped the animals concerned to find a more secure niche in the now teeming web of life.
And within that web of life microscopic organisms were also diversifying, using silica rather than calcium to make structural improvements. Today this diversity is seen in the micro-plankton that include beautiful diatoms near the surface of the ocean.
And so in several aquatic ecosystems within Earth’s salt waters and fresh waters, plants and animals developed extremely diverse ways of living, including different kinds of asexual and sexual reproduction.
But male and female animal cells were still ejected into the water en masse, with only some managing to pair off. Each resulting egg contained instructions so that the hatchling could develop independently of its parents – but only if it was one of the few that survived infancy. This method of generational transfer is still widespread in aquatic ecosystems today.
Meanwhile tectonic plate movement, driven by activity deep within our planet, had created the huge supercontinent Gondwana and several lesser landmasses. And there were some cosmic players beyond Earth that hadn’t yet made their presence felt.
* * * * * * *
(courses.bio.psu.edu)Photosynthetic diatoms are very important from a global perspective,
being responsible for perhaps 20% of annual global carbon fixation.
They are encased in a glass-like silica shell, invisible to the naked eye,
and are exceptionally beautiful structures.
Each one consists of two components that fit together, like the bottom and lid of a pillbox.
After the death of individual diatoms,
their microscopic shells sink and gradually form thick layers of sediment (diatomaceous earth).
Living diatoms avoid sinking by regulating their cellular ion concentrations.
(Another Google image)
I intend to post one Age each month until December,
and then the Epilogue and Two-Page Timeline in January.
If you would rather have a free email copy of the book, please sign in to my Guestbook
(see my first post: An Introduction),
making sure that you ask for your entry to be kept private.
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