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Answer:
Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells. Cells first emerged at least 3.8 billion years ago. This was approximately 750 million years after the earth was formed.The origin of cells was the most important step in the evolution of life on Earth. The birth of the cell marked the passage from pre-biotic chemistry to partitioned units resembling modern cells. The final transition to living entities that fulfill all the definitions of modern cells depended on the ability to evolve effectively by natural selection. This transition has been called the Darwinian transition.
If life is viewed from the point of view of replicator molecules, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to keep complex molecules stable in a varying and sometimes aggressive environment; the latter is fundamental for the evolution of biocomplexity. If the freely floating molecules that code for enzymes are not enclosed in cells, the enzymes will automatically benefit the neighbouring replicator molecules. The consequences of diffusion in non-partitioned life forms might be viewed as "parasitism by default." Therefore, the selection pressure on replicator molecules will be lower, as the 'lucky' molecule that produces the better enzyme has no definitive advantage over its close neighbors. If the molecule is enclosed in a cell membrane, then the enzymes coded will be available only to the replicator molecule itself. That molecule will uniquely benefit from the enzymes it codes for, increasing individuality and thus accelerating natural selection.
Answer:
Take it from biology
Explanation:
The history of evolution of cells is the evolution of human cells how can they evolute and why they evolute take help from this note.
All life on Earth evolved from a single-celled organism that lived roughly 3.5 billion years ago, a new study seems to confirm.
The study supports the widely held "universal common ancestor" theory first proposed by Charles Darwin more than 150 years ago.
(Pictures: "Seven Major 'Missing Links' Since Darwin.")
Using computer models and statistical methods, biochemist Douglas Theobald calculated the odds that all species from the three main groups, or "domains," of life evolved from a common ancestor—versus, say, descending from several different life-forms or arising in their present form, Adam and Eve style.
The domains are bacteria, bacteria-like microbes called Archaea, and eukaryotes, the group that includes plants and other multicellular species, such as humans.
The "best competing multiple ancestry hypothesis" has one species giving rise to bacteria and one giving rise to Archaea and eukaryotes, said Theobald, a biochemist at Brandeis University in Waltham, Massachusetts.
But, based on the new analysis, the odds of that are "just astronomically enormous," he said. "The number's so big, it's kind of silly to say it"—1 in 10 to the 2,680th power, or 1 followed by 2,680 zeros.
(Also see "Evolution Less Accepted in U.S. Than Other Western Countries, Study Finds.")
Theobald also tested the creationist idea that humans arose in their current form and have no evolutionary ancestors.
The statistical analysis showed that the independent origin of humans is "an absolutely horrible hypothesis," Theobald said, adding that the probability that humans were created separately from everything else is 1 in 10 to the 6,000th power.
(As of publication time, requests for interviews with several creationist scientists had been either declined or unanswered.)
(Related pictures: "Evolution vs. Intelligent Design: Six Bones of Contention.")
Putting Darwin to the Test
All species in all three domains share 23 universal proteins, though the proteins' DNA sequences—instructions written in the As, Cs, Gs, and Ts of DNA bases—differ slightly among the three domains (quick genetics overview).
The 23 universal proteins perform fundamental cellular activities, such as DNA replication and the translation of DNA into proteins, and are crucial to the survival of all known life-forms—from the smallest microbes to blue whales.
A universal common ancestor is generally assumed to be the reason the 23 proteins are as similar as they are, Theobald said.
That's because, if the original protein set was the same for all creatures, a relatively small number of mutations would have been needed to arrive at the modern proteins, he said. If life arose from multiple species—each with a different set of proteins—many more mutations would have been required.
But Theobald hoped to go beyond conventional wisdom.
"What I wanted to do was not make the assumption that similar traits imply a shared ancestry ... because we know that's not always true," Theobald said.
"For instance, you could get similarities that are not due to common ancestry but that are due to natural selection"—that is, when environmental forces, such as predators or climate, result in certain mutations taking hold, such as claws or thicker fur.
Biologists call the independent development of similar traits in different lineages "convergent evolution." The wings of bats, birds, and insects are prime examples: They perform similar functions but evolved independently of one another.
But it's highly unlikely that the protein groups would have independently evolved into such similar DNA sequences, according to the new study, to be published tomorrow in the journal Nature.
"I asked, What's the probability that I would see a human DNA polymerase [protein] sequence and another protein with an E. coli DNA polymerase sequence?" he explained.
"It turns out that probability is much higher if you use the hypothesis that [humans and E. coli] are actually related."
(Related: "Future Humans: Four Ways We May, or May Not, Evolve.")
No Special Treatment for Evolutionary Theory?
David Penny, an evolutionary biologist at Massey University in New Zealand, called the grand scope of Theobald's study "bold."
Penny had been part of a similar, but more narrowly focused, study in the 1980s. His team had looked at shared proteins in mammals and concluded that different mammalian species are likely descended from a common ancestor.
Testing the theory of universal common ancestry is important, because biologists should question their major tenets just as scientists in other fields do, said Penny, who wasn't part of the new study.
"Evolution," he said, "should not be given any special status."