Evolution question: Why is it always said that we all come from a single ancestor?

Question

We being defined as, I dunno, the domain eukarya or something.

Anyways, could we (original organisms, etc.) not have "abiogenesized" in multiple parts of the earth near simultaneously and (maybe) come from different ancestors that eventually evolved to interbreed?

Answer 1

There is a disturbing trend of scientists, teachers, and students coming under attack for expressing support in the theory of intelligent design, or even just questioning evolution. The freedom of scientists, teachers, and students to question Darwin's theory, or to express alternative scientific hypothesis is coming under increasing attack by people that can only be called Darwinian fundamentalists.”

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Answer 2

By the way, to yehoshooa adam: What mental institute did you escape from? An ex-government scientist, familiar with evolution experiments? Did they plant electrodes in your head?

Anyway, to the question, first off, two evolutionary lines evolving to converge enough to interbreed is a statistical impossibility. Not that that's really relevant to your question.

Due to the similarities in the DNA structure of all living things so far discovered, we can say that within all likelihood, all forms of life so far discovered descended from a single common ancestor. If there were any other beginnings, they didn't leave any living descendants that we've found.

Because it was a rather unlikely event, the most probable scenario is that it only happened once.

Answer 3

Short answer, there is no known evidence for it, no known mechanism for non-breeding lines to ever *gain* the ability to interbreed, and many reasons why it would not occur.

It would be theoretically possible, (and fully consistent with the theory of evolution) for life to have started in several places simultaneously and continued evolving along parallel lines ... but the genetic and DNA evidence indicates that there are not multiple lines ... but only one. In other words, there are enough DNA commonalities (right down to letter-for-letter identical strings of genetic material, shared between all life forms from vertebrates, to plants, to fungi, to prokaryotes, and eukaryotes) that these all seem to be from the same strain.

As far as separate lines converging ... there is no known mechanism for this to have happened. Even as it is ... once a species has split into two separately breeding species, it is almost impossible for them to *regain* the ability to interbreed. So if two branches never had the ability to interbreed in the first place, the odds of ever evolving into something that could interbreed would be too small to imagine.

So the "single-ancestor" explanation, is just the simplest explanation for the current evidence.

Answer 4

all eukaryotes are said to come from the same ancestor organisms (which is said to be the decendent of an archaea) because at the DNA level we have homology with just about all eukaryotes in some way shape or form. When it comes to Mammals, most mammals have very similar DNA with only about 1-15% differing ( I am just throwing this numer out, consider man and ape are about 98% homologous but i am sure elephant and rabbit may be 90%?). This is mainly due to that fact that most of our DNA (to our knowledge) does not code for anything, or atleast anything that would be expressed into protein. This "junk DNA" is conserved pretty well throughout eukaryotes. Proteins are even conserved throughout eukaryotes, a fly and a human can even have homology within their DNA with proteins, this does not mean that it has to be 100% right on, however from my personal research i can tell you that some neuronal proteins in flies and humans have up to 30% homology...... This would tell us that we must have all arose from some sort of common ancestor and through the hundread of millions even billions of years of evolution have adapted to our own environment using this basic machinary that we were all given. Plants too... fungus..... all eukaryotes have some homology....

Answer 5

DNA suggests that all organisms have common ancestry. While this doesn't rule out the possibility of some sort of melding of different organisms at a very early time, an event like that, based on the current understanding of biology, is highly unlikely. What would be more likely is that if other forms of organisms originated, they died very quickly due to factors such as environmental change, domination of niche, or good 'old survival of the fittest.

Answer 6

well wheater you believe in evolution or not, that seem to be the common consesus. and yes it is true everyone beguins as a polywog, looking for a mate to egg on. but that does not prove evolution, that has never actualy been observed to happen that way. and without 100% observeable of 100 out of 100 time, duplicateable by at least ten other independant scientists. it cannot be considered as a scientific fact, for acceptance as a law factualy. assumed fanaticial imaginations does not make anything a scientific fact. as far as i am concerned as an ex-scientist. these religious fanatics with their religion of evolution have not proven their case, any more than the christians have proved theirs, about the guy with a faked name, the name that could not of existed 2000 years ago. about a thousand years before the j was even invented.

Answer 7

there is i think some controversy concerning the early phase of evolution, about whether the majority of gene transfer is 'vertical' (transfer by heredity) which produces a birfurcating tree with a single root, or perhaps horizontal gene transfer (non-hereditary transfer, by virus activity for instance) is important. this would produce a pattern more like a web. recent evidence seems to favour the web view - life is still probably all from a single ancestor, but identifying it is trickier.

Answer 8

Well, it could be a possibility, but the fact that we are all DNA based life forms, have cells with roughly the same structure and the first ones only reproduced asexually (thus making interbreeding impossible for the first billion of years of life or so) makes it highly unlikely.

Answer 9

Hello,, I believe it to be true ,if you reversed the clock and started eliminating the growth of the world population eventually you would arrive at a point in time where nobody was around and only microbes and aliens were breeding. Sound kinda like Washington D.C.

Answer 10

Occam's razor: the simplest explanation is most likely the right one.