plants and animals--common ancestor?

[CookingWithGas]

I have read discussions about evolution that mention how long ago the human line branched off from other lines based on the variations in the DNA. Lots of animals have common ancestors if you go back far enough. Maybe there is even a single organism that branched into all animals known today.

Both plants and animals are alive, and have DNA. Could there have been a single organism back in the very first genesis of life that spawned both plants and animals? Or are these two things so distinct that they had to have distinct origins? Has anyone ever compared human DNA to a dandelion?

[Podkayne]

Not a dandelion. . . will a banana do? The banana genome has been mapped (a giant leap forward for science!), and we humans have about 30% of our genes in common with bananas.

Plants and animals have a common ancestor that was neither a plant nor an animal, just like humans and chimps have a common ancestor that was neither a human or a chip, and you and your cousin have a common ancestors, grandma and grandpa, who are neither you nor your cousin.

Animals and plants are both eukaryotes, which are cells with nuclei. They are different from bacteria–though, of course, plants and animals have common ancestor with bacteria. The most “primtive” life forms, those closest to the “root” of the tree of life are archea, the extremophiles. (Seems like everything’s “extreme” these days, doesn’t it?) Extremophiles are bacteria that live in extremely hot or cold or acidic or salty environoments.

It may be that life actually started in these environoments. It also could be that life started in gentle environments, some forms evolved to cope with these extreme environoments, and then all life except the extremophiles, which can live deep in the ocean by vents of boiling water, or deep in the earth, or deep under ice was wiped out–by asteroid impact, for example, leaving only extremophiles to repopulate the earth by evolving into all the life forms we see today.

[Podkayne]

Doh! Pardon, “which are cells with nuclei,” should be “which have cells with nuclei”!

[Colibri]

As Podkayne implies, all life on earth shares a common ancestor, as demonstrated by theGenetic Code, which is (with minor exceptions) the same for all known organisms.

From the site:

. . .the Genetic Code in the table above has also been called “The Universal Genetic Code”. It is known as “universal”, because it is used by all known organisms as a code for DNA, mRNA, and tRNA. The universality of the genetic code encompases animals (including humans), plants, fungi, archaea, bacteria, and viruses. However, all rules have their exceptions, and such is the case with the Genetic Code; small variations in the code exist in mitochondria and certain microbes. Nonetheless, it should be emphasized that these variances represent only a small fraction of known cases, and that the Genetic Code applies quite broadly, certainly to all known nuclear genes.

Note that there is no particular reason for any specific combination of nucleotides to code for a particular amino acid. The genetic code is (mostly) as arbitrary as Morse Code. If we ever did discover an organism in which most codons coded for different amino acids, it could be considered evidence for extraterrestrial origin.