All life on earth

 

All life on earth - everything from bacteria to mushrooms to hippos - shares an astonishing range of detailed biochemical similarities, including the structure of heredity in DNA and RNA, and the universal use of ATP as an energy-storing compound. Two possible scenarios, with markedly different implications for the nature of life, might explain these regularities: either all earthly life shares these features because no other chemistry can work, or these similarities only record the common descent of all organisms on earth from a single origin that happened to feature this chemistry as one possibility among many.
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"War of the Worldviews", p. 352

 

Stephen Jay Gould

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The Second Law of Thermodynamics states that all energy systems run down like a clock and never rewind themselves. But life not only 'runs up,' converting low energy sea-water, sunlight and air into high-energy chemicals, it keeps multiplying itself into more and better clocks that keep 'running up' faster and faster. Why, for example, should a group of simple, stable compounds of carbon, hydrogen, oxygen and nitrogen struggle for billions of years to organize themselves into a professor of chemistry? What's the motive? If we leave a chemistry professor out on a rock in the sun long enough the forces of nature will convert him into simple compounds of carbon, oxygen, hydrogen and nitrogen, calcium, phosphorus, and small amounts of other minerals. It's a one-way reaction. No matter what kind of chemistry professor we use and no matter what process we use we can't turn these compounds back into a chemistry professor. Chemistry professors are unstable mixtures of predominantly unstable compounds which, in the exclusive presence of the sun's heat, decay irreversibly into simpler organic and inorganic compounds. That's a scientific fact. The question is: Then why does nature reverse this process? What on earth causes the inorganic compounds to go the other way? It isn't the sun's energy. We just saw what the sun's energy did. It has to be something else. What is it?

 

Robert M. Pirsig

 

Unfortunately, all life on earth - the only life we know - represents, for all its current variety, the results of a single experiment, for every earthly species evolved from the common ancestry of a single origin. We desperately need a repetition of the experiment (several would be better, but let's not be greedy!) in order to make a judgement. Mars represents our first real hope for a second experiment - the sine qua non - for any proper answer for the question of questions.

 

Stephen Jay Gould

 

All my life, I've wondered about life beyond the earth. On those countless other planets that we think circle other suns, is there also life? Might the beings of other worlds resemble us, or would they be astonishingly different? What would they be made of? In the vast Milky Way galaxy, how common is what we call life? The nature of life on earth and the quest for life elsewhere are the two sides of the same question: the search for who we are.

 

Carl Sagan

 

Many similarities of basic design among animal phyla, once so confidently attributed to convergence, and viewed as testimony to the power of natural selection to craft exquisite adaptation, demand the opposite interpretation that Mayr labeled as inconceivable: the similar features are homologies, or products of the same genes, inherited from a common ancestor and never altered enough by subsequent evolution to erase their comparable structure and function. The similarities record the constraining power of conserved history, not the architectural skills of natural selection independently pursuing an optimal design in separate lineages. Vertebrates are, in a certain sense, true brothers (or homologs) - not mere analogs - of worms and insects.

 

Stephen Jay Gould

 

It is the sun that shares our works.
The moon shares nothing. It is a sea.
When shall I come to say of the sun,
It is a sea; it shares nothing;
The sun no longer shares our works
And the earth is alive with creeping men,
Mechanical beetles never quite warm?
And shall I then stand in the sun, as now
I stand in the moon, and call it good,
The immaculate, the merciful good,
Detached from us, from things as they are?
Not to be part of the sun? To stand
Remote and call it merciful?
The strings are cold on the blue guitar.

 

Wallace Stevens