Where Did the First Living Cell Come From?

[THE FUGITIVE]

n order for the principles of mutation and natural selection in the theory of evolution to work, there have to be living things for them to work on. Life must exist before it can to start diversifying. Life had to come from somewhere, and the theory of evolution proposes that it arose spontaneously out of the inert chemicals of planet Earth perhaps 4 billion years ago.

Could life arise spontaneously? If you read How Cells Work, you can see that even a primitive cell like an E. coli bacteria -- one of the simplest life forms in existence today -- is amazingly complex. Following the E. coli model, a cell would have to contain at an absolute minimum:

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A cell wall of some sort to contain the cell
A genetic blueprint for the cell (in the form of DNA)
An enzyme capable of copying information out of the genetic blueprint to manufacture new proteins and enzymes
An enzyme capable of manufacturing new enzymes, along with all of the building blocks for those enzymes
An enzyme that can build cell walls
An enzyme able to copy the genetic material in preparation for cell splitting (reproduction)
An enzyme or enzymes able to take care of all of the other operations of splitting one cell into two to implement reproduction (For example, something has to get the second copy of the genetic material separated from the first, and then the cell wall has to split and seal over in the two new cells.)
Enzymes able to manufacture energy molecules to power all of the previously mentioned enzymes
Obviously, the E. coli cell itself is the product of billions of years of evolution, so it is complex and intricate -- much more complex than the first living cells. Even so, the first living cells had to possess:

A cell wall
The ability to maintain and expand the cell wall (grow)
The ability to process "food" (other molecules floating outside the cell) to create energy
The ability to split itself to reproduce
Otherwise, it is not really a cell and it is not really alive. To try to imagine a primordial cell with these capabilities spontaneously creating itself, it is helpful to consider some simplifying assumptions. For example:

Perhaps the original energy molecule was very different from the mechanism found in living cells today, and the energy molecules happened to be abundant and free-floating in the environment. Therefore, the original cell would not have had to manufacture them.
Perhaps the chemical composition of the Earth was conducive to the spontaneous production of protein chains, so the oceans were filled with unimaginable numbers of random chains and enzymes.
Perhaps the first cell walls were naturally forming lipid spheres, and these spheres randomly entrapped different combinations of chemicals.
Perhaps the first genetic blueprint was something other than DNA.
These examples do simplify the requirements for the "original cell," but it is still a long way to spontaneous generation of life. Perhaps the first living cells were completely different from what we see today, and no one has yet imagined what they might have been like. Speaking in general terms, life can only have come from one of two possible places:

Spontaneous creation - Random chemical processes created the first living cell.
Supernatural creation - God or some other supernatural power created the first living cell.
And it doesn't really matter if aliens or meteorites brought the first living cell to earth, because the aliens would have come into existence through either spontaneous creation or supernatural creation at some point -- something had to create the first alien cells.

Most likely, it will be many years before research can completely answer any of the three questions mentioned here. Given that DNA was not discovered until the 1950s, the research on this complicated molecule is still in its infancy, and we have much to learn.

National Geographic below---

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 ancestorâ€"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"â€"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 sequencesâ€"instructions written in the As, Cs, Gs, and Ts of DNA basesâ€"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-formsâ€"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 speciesâ€"each with a different set of proteinsâ€"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"â€"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."

Editor's note: Two corrections have been made to this article. In the first sentence "million" has been changed to "billion." In the seventh paragraph, "10 followed by 2,680 zeros" has been changed to "1 followed by 2,680 zeros." Many thanks to readers for pointing out these typos.