Encyclopedia of Evolution.pdf - Online Reading Center

Further Reading
Wise, Steven M. Rattling the Cage: Toward Legal Rights for Animals.
Boston: Perseus, 2000.
———. Science and the Case for Animal Rights. Boston: Perseus,
2002.
anthropic principle The anthropic principle is the concept
that the universe has characteristics that, beyond coincidence,
have allowed the evolution of intelligence. Because the proponents
(mainly cosmologists) of this concept do not specify that
a higher being is responsible for creating these characteristics,
the anthropic principle differs from creationism and intelligent
design, which attribute all complexity to a creative
intelligence. First named in 1973 by cosmologist Brandon
Carter, the anthropic principle maintains that human observers
can deduce certain characteristics about the universe simply
from the fact that they exist and are capable of studying
it. In its strongest form, the anthropic principle insists that
no universe could exist that did not have characteristics that
would allow the evolution of intelligence at some point in its
history. This principle relates to evolutionary science in that,
if the principle is true, the evolution of intelligence could not
have been a contingent (or chance) event.
Many cosmologists, such as the British Astronomer
Royal Sir Martin Rees, consider the anthropic principle to be
a tautology: Humans are here because humans are here. Others
claim that it provides useful insights. From the evolutionary
perspective, to say “the universe is just right for life” is
backward; instead, life has evolved to fit the conditions of the
universe. If the conditions had been different, life would have
evolved differently. Anthropic theorists point out that physical
constants of matter and energy took form during the first
brief moments after the big bang (see universe, origin of)
and that if these constants had been just a little bit different,
nothing remotely resembling life could have evolved at all.
They present examples such as these:
• During the expansion of the universe right after the big
bang, small deviations from the uniform field of energy
precipitated the formation of galaxies and stars. If those
deviations had been slightly less, galaxies and stars would
never have condensed; if those deviations had been slightly
more, all the matter in the universe would have condensed
into massive black holes.
• A force known as the strong nuclear force, one of the four
fundamental forces, holds protons and neutrons together.
If the strong nuclear force had been even 2 percent stronger
than it is, protons would have bound into diproton pairs,
which would have become helium atoms, and the universe
would have had no hydrogen atoms. Helium atoms are
very nonreactive, and nothing much would have happened
in the universe, which might have been a helium cloud for
all eternity. Hydrogen, on the other hand, undergoes thermonuclear
reactions (producing helium) that allow stars to
ignite.
• During atomic fusion, seven one-thousandths of the mass
of the hydrogen becomes energy, while the rest of the mass
becomes helium. If more energy were lost during fusion,
anthropic principle
all of the energy would have been used up by now. If
just slightly less energy were lost, fusion would not have
occurred at all and the universe would consist only of
hydrogen.
• A slight difference in atomic forces might also have prevented
the formation of carbon atoms in the interior of
large stars. Without carbon, life may not have been possible
(see origin of life).
• The force of gravity seems to be just right. If the force of
gravity had been slightly more, stars such as the Sun would
have burned out in less than a year; if the force had been
slightly less, stars would never have condensed and ignited
at all.
Because the physical constants are “just right” for the evolution
of intelligence, the anthropic principle has been called
the “Goldilocks principle,” both by admirers and detractors.
Anthropic theorists ask, could all this just be good luck?
Another possible example of a cosmic coincidence is that
the cosmological constant is much smaller than it might have
been. Physicist Albert Einstein posited a cosmological constant
in his 1917 theory of the history of the universe. This
constant is a number in the equation that accounts for the
presence of dark energy, which is invisible but which causes
the universe to expand faster as time goes on. Later, Einstein
concluded that there was no empirical evidence that this was
occurring, and he called the cosmological constant his “greatest
blunder.” Some evidence from the late 1990s suggests that
the rate of expansion of the universe may itself be increasing,
making it the first evidence to be consistent with a cosmological
constant. Cosmologists remain unsure whether there
even is a cosmological constant, but if there is, humans are
pretty lucky that it is not any bigger than it is, or the universe
would have expanded so fast that galaxies and stars would
never have formed.
Life is possible on Earth because of water. Water is a
molecule with highly unusual properties, mostly because the
molecules stick together with hydrogen bonds. If the laws
of chemistry had been slightly different, such that hydrogen
bonds could not form, there would have been no life on Earth,
or presumably anywhere else in the universe. This represents a
non-cosmological example of the anthropic argument.
Rees and other cosmologists point out that if Earth had
been a little different, life could not have evolved. If it had
been a little larger, or a little smaller; a little closer to the
Sun, or a little further away, no life of any kind could have
evolved. So unusual are the conditions of the Earth that some
scientists have suggested that, although bacteria-like lifeforms
may be abundant on planets throughout the universe,
complex life may be exceedingly rare and may not even exist
anywhere else (see essay, “Are Humans Alone in the Universe?”).
Given the possibility that there may be an uncountable
number of Earth-like planets in the universe, it may not
be unlikely (indeed, it may be inevitable) that intelligent life
would have evolved.
The anthropic principle suggests that there is only one
universe, and it is one that is strangely suitable for intelligent
life. Some cosmologists, such as Rees, have suggested