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On the topic of evolution, are we distant cousins to, say, a blade of grass?

  1. Dec 20, 2012 #1
    Are we distant cousins to every single blade of grass and every single plant and animal on earth? Also, if all life on earth had a single origin somewhere in the ocean, how did grass and plant life spread throughout the world so quickly?
  2. jcsd
  3. Dec 20, 2012 #2


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    Yes, it can be put this way.

    These things are completely unrelated, no idea what you are asking about. Besides - define quickly. If it took a million years for some genus/species to spread through a world on the geological scale it was a blink, but it means just a 20 meters per year (assuming you start from a single point and 40000 km circumference).
  4. Dec 20, 2012 #3


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    As Borek says, evolution has had a long time to work, so the answer to your question may not require multiple origins of life. Nonetheless, it is unclear whether universal common ancestry corresponds to a "single origin". Theobald (Nature, 2010), reporting on a statistical test in favour of universal common ancestry, writes:

    "The theory of UCA allows for the possibility of multiple independent origins of life. If life began multiple times, UCA requires a ‘bottleneck’ in evolution in which descendants of only one of the independent origins have survived exclusively until the present (and the rest have become extinct), or, multiple populations with independent, separate origins convergently gained the ability to exchange essential genetic material (in effect, to become one species). All of the models examined here are compatible with multiple origins in both the above schemes, and therefore the tests reported here are designed to discriminate specifically between UCA and multiple ancestry, rather than between single and multiple origins of life. Furthermore, UCA does not demand that the last universal common ancestor was a single organism, in accord with the traditional evolutionary view that common ancestors of species are groups, not individuals. Rather, the last universal common ancestor may have comprised a population of organisms with different genotypes that lived in different places at different times."
  5. Dec 20, 2012 #4


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    Another thing to remember is that at one time all of the continents were a single mass, they were not separated by vast distances as they are today. The continents eventually split up and drifted apart.

  6. Dec 20, 2012 #5
    Yes, that is highly probable. Multiple points of origin do not logically contradict the theory of evolution. However, evidence collected so far is consistent with there being only one point of origin for life. Every organism that you know about probably has a common ancestor that lived about 4.1 BYA.
    It depends on what you call plant life. I will restrict this discussion to eukaryotes that contain chloroplasts with chlorophyll. There are green bacteria that use a compound with cyanide to gather energy from sunlight. I don't think of them as plants. However, some other scientists prefer to call them plants.

    The paleontological evidence suggests that the first grasses evolved about 100 MYA, but remained restricted to certain parts of the earth for a long time. They did not immediately spread everywhere. Grasses became common all over the earth about 55 MYA. Scientists are still trying to figure out how they spread.

    There were no plants on land until the Silurian, more than 450 MYA. Most of these were very small. The first large land plants evolved late in the Devonian.

    There appear to be some microscopic plants alive in the oceans of the Cambrian, about 550 MYA. There are no fossils of true plants before 1 BYA. Before 780 MYA, the only fossils are those of bacteria. Plants and animals don't appear in the fossil record until about 780 MYA. So it took about 3.1 BY for the simplest plants and animals to evolve from bacteria.

    There do not seem to be any plants that lived anywhere before 570 MYA. There are some blue green cyanobacteria that lived about 4 BYA. They are the earliest forms of life that fossilized. As I said, I don't count them as plants.

    However you define plant, it took millions of years for plants to spread all around the planet. Even the little step of moving from water onto dry land took at least 50 MY. The flowering plants on land took about 50 MY to spread all over the planet. So it appears that plants took a long while to spread.
  7. Dec 23, 2012 #6
    Some misinformation from Darwin123:
    The 'cyan' in their name is not a reference to cyanide. It is a color, and these are alternatively referred to as blue-green bacteria or blue-green algae. Their photosynthetic material is chlorophyll, and theory suggests that cyanobacteria are the origin of plant chloroplasts. There are a few other bacteria using novel compounds for photosynthesis, such as retinal in halobacteria, but none are using cyanide.
  8. Dec 23, 2012 #7
    Actually, the "chlorophyl molecules" in cyanobacteria do contain cyano group ligands that are complexed with a metal. That is why they have the greenish-blue color.

    You probably have it backwards. The cyano-group got its name from the colors the coordinate compounds take on with cyano group ligands.

    However, it doesn't matter. I was trying to communicate a point.

    Plants did not spread overnight. They did not even appear overnight. The OP is apparently imaging the multicellular plants and animals that he can see today, without a microscope. In actual fact, both plants and animals have simple ancestors which don't appear in any way like the large plants and animals that we can see today.

    The OP is free to correct me if I am wrong. However, the OP seems to be talking about flowering plants (i.e., angiosperms). About 85% of the land plants that we see around us with the unaided eye are flowering plants. Maybe 10% of land plants seen with the unaided eye are either gymnosperms, horsetails or ferns. The other plants are either microscopic, marine or rare. He isn't thinking about those.

    The large plants that we see were not around for most of the earths history. Even after they evolved, they did not spread all over the world overnight. They were still limited by slow processes including continental drift. It actually took them a long time to evolve. However, plants took an even longer time to evolve. For most of the earth's history, there were no plants. There were only bacteria.

    All plants and animals seem to have evolved from bacteria. Bacteria are simple organisms that don't look anything like true plants and true animals.

    Cyanobacteria do a lot of things that plants do. They take in carbon dioxide, absorb sunlight, and breath out oxygen. Although there are some species of cyano bacteria today, there is evidence that they existed as long as 3 billion years ago. Many species of cyanobacteria have probably gone extinct, but some species have evolved since then.

    All eukaryotes are probably descended from extinct forms of cyanobacteria. The only fossils that we have that are older than 1 BY are cyanobacteria. Parts of our cells, especially the mitochondria, are similar to cyanobacteria. However, a cyanobacteria is not a full plant or animal by most standards.

    Both plants and animals probably have cyanobacteria as common ancestors. Not as most recent common ancestors, but still common ancestors. Therefore, I hesitate to say that they are plants. They are so simple in structure that they don't resemble plants.

    Cyanobacteria make pond scum look complex. Most pond scum are single celled eukaryotes with chlorophyll. Pond scum is arguably true plants. However, we have no idea how fast they spread through the world.

    Therefore, to ask that plants spread so rapidly is misleading. Plants did not spread through the world rapidly. The spread of plants was very slow, and overlapped the spread of animals which was also very slow. The plants that the OP probably knows best, the angiosperms, are geologically speaking recent phenomenon. The earlier plants took a long time to evolve and spread onto land.

    Plants did not evolve in one place. Their ancestors, the cyanobacteria, may have evolved in one place. The cyanobacteria that lived in the oceans "only" took 200 MY to spread around the oceans. The land really took a long time to be colonized by any living things.
  9. Dec 24, 2012 #8


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    Can you show us a structure? As far as I can tell (but I admit this is not my area of expertise) cyanobacteria use phycocyanine, it has nothing to do with cyanides (which is what I suppose you mean by cyano group ligands).
  10. Dec 24, 2012 #9
    You are completely right. I got the two confused.

    I am the innocent victim of an urban legend. Cyanobacteria are contain microcystin, a cyanotoxin that has nothing to do with the cyano group.

    Cyclic heptapeptides found in MICROCYSTIS and other CYANOBACTERIA. Hepatotoxic and carcinogenic effects have been noted. They are sometimes called cyanotoxins, which should not be confused with chemicals containing a cyano group (CN) which are toxic.”

    Thank you for correcting me. I was the innocent victim of an urban legend. People have been referring to cyanotoxins as cyanide. However, that is really a type of chemical nickname.

    Here is a link in which cyanotoxins are called cyanide. Contrary to this link, cyanotoxins are NOT cyanide compounds.
    “Other reports have suggested that ALL species of Cyanobacteria produce "cyanotoxins" and "cyanide" when killed rapidly. Geosim, a cause of off-flavors in fish, is similarly released by Cyanobacteria, when cells are stressed by fish/animal ingestion or by application of a biocide to the pond, lake, reservoir or river where they reside.”

    It is likely that the chloroplasts in plants evolved from cyanobacteria. It is interesting that the rest of a plant cell was not descended from cyanobacteria.

    One may think of a cyanobacterium as “half a plant cell”. A cyanobacterium is like a chloroplast struggling to make ends meet on its own.

    “Chloroplasts found in eukaryotes (algae and plants) likely evolved from an endosymbiotic relation with cyanobacteria. This endosymbiotic theory is supported by various structural and genetic similarities.[11] Primary chloroplasts are found among the "true plants" or green plants – species ranging from sea lettuce to evergreens and flowers which contain chlorophyll b – as well as among the red algae and glaucophytes, marine species which contain phycobilins. It now appears that these chloroplasts probably had a single origin, in an ancestor of the clade called Archaeplastida. Other algae likely took their chloroplasts from these forms by secondary endosymbiosis or ingestion.”

    I hope you don't ding me for this infringement of the rules. I promise to be good from now on!
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