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by
Science@Nasa
Picking Up Where D'Arcy Thompson
Left Off
May 28, 1999: During the May 18th
press conference announcing Nobel Laureate Dr. Baruch Blumberg as the new
head of NASA's Astrobiology Institute, Blumberg posed a challenge to the
scientific community." The mission is to look for life without any
specifications. Nothing in the mission would preclude looking for rather
strange and unusual life forms that we can't even imagine right now," said
Blumberg. NASA Administrator Dan Goldin concurred, stating, "We're looking
for any form of biological life. Single-cell (organisms) would be a grand
slam." In order to effectively search for life on other planets, we first
have to come to an understanding about what life IS. One way to do this is
to study the forms that life can take.
In his 1917 work, "On Growth and
Form," D'Arcy Thompson altered mathematical functions in order to
visualize how species changed shape over time. NASA scientists are using
Thompson's biomathematical studies of life forms on Earth to postulate
about life forms throughout the universe. There are certain universal
conditions that will always affect the shape of a life form, wherever that
life may be." Everywhere Nature works true to scale, and everything has a
proper size accordingly," wrote Thomspon. "Cell and tissue, shell and
bone, leaf and flower are so many portions of matter, and it is in
obedience to the laws of physics that their particles have been moved,
moulded and conformed." Gravity, for instance, acts on all particles and
affects matter cohesion, chemical affinity and body volume. Other
influences that are consistent throughout the universe are temperature,
pressure, electrical charge and chemistry. But before we can conduct a
comprehensive search for unknown extraterrestrial forms of life, there
needs to be an extensive classification of known life forms on Earth. The
history of life on Earth provides us with a good model for how life can
evolve in the universe. Fossils, even microbial fossils, can tell us a
great deal about all the different life forms that have at one time or
another shown their face on our planet." Some fossils in the ancient
Burgess shale are so alien we can't determine which end of the creatures
are up, and yet these monsters evolved right here on Earth from the same
origins that we did," wrote Johan Forsberg, a Swedish psychologist. By
becoming forensic scientists, researchers at the Space Sciences Laboratory
at the Marshall Space Flight Center can develop an encyclopedia of
microbial life forms that have developed on Earth. Because so many life
forms need to be catalogued, the scientists are working to develop a
"D'Arcy Machine" to help them create a comprehensive "Book of Life."
This Book of Life project has three phases. Phase 1 - compiling a
beginning database of microbial life forms - has already been completed.
This image database is composed of 10,000 examples and distinguishes the
basic microbial shapes such as rods, spheres, filaments, clusters that
look like grapes (cocci), and spirochete (spirals). A computer neural
network has been trained to recognize and classify these microbial life
forms with 90 percent accuracy. Phase 2 of the project will expand the
basic database by using a more powerful neural network. Funds from the
NASA Advanced Concepts Office provided Marshall scientists with a
Beowulf-class parallel computer. NASA developed the Beowulf Project to
address scientific problems associated with large data sets. Scientists at
Marshall have named the new parallel computer "Leibniz," after the German
mathematician whose lifelong goal was to organize all human knowledge.
This computer system will expand the image database by acquiring and
classifying new and ambiguous images. To discriminate organic life forms
from inorganic shapes, microbiologists often use the vague criteria, "Does
it look alive to you?" A parallel computer using pattern recognition can
make this task easier and more exact by breaking the starting image down
into identifiable parts." Human judgement is still very much depended upon
for identifying microbial life forms," says Dr. David Noever of NASA's
Marshall Space Flight Center. "Automated filters would be much like the
filters commonly used to sort out useful e-mails from useless ones. The
user of the neural network would get a morning menu of microbial
candidates for further detective work." Although the trained human eye is
better at recognizing microbial life forms, using a computer "filter" to
check for life-like patterns could help cut the immense scale of the Book
of Life project down to a more manageable size.
By Phase 3 of the project, the
neural network will be so advanced in its learning that it will be able to
acquire and classify new images with minimal human supervision. This
network would then be equipped for future search scenarios, including the
examination of meteorites found on Earth and samples retrieved from lunar
or interplanetary space missions. This advanced neural network will be a
fast and efficient classifier of the vast amount of microbial images that
will need to catalogued.
A Big ProblemThis speed and efficiency are extremely important due to the
detail with which the samples must be analyzed. Not only are there a lot
of samples to study, but there are multiple dimensions to consider. D'Arcy
Thompson used mostly linear and quadratic maps to compare different life
forms. Linear maps between two shapes require four coefficient variables,
while quadratic maps use 10 variables.Thompson wrote in "On Growth and
Form," "I know that in the study of material things number, order, and
position are the threefold clue to exact knowledge: and that these three,
in the mathematician's hands, furnish the first outlines for a sketch of
the Universe." While Thompson and other biomathematicians used almost
exclusively linear and quadratic distortions to study how life forms
change over time, it is unlikely that complex life forms throughout the
universe will be confined to these narrow statistical relationships. In a
paper presented last September at the 50th anniversary D'Arcy Thompson
conference in Dundee, Scotland, Noever asked, "What if D'Arcy had had a
computer?" When D'Arcy Thompson introduced the idea of studying organisms
by their geometric shapes, he could only draw figures by hand. The
computers of today can take Thompson's research much further. By
repeatedly comparing and contrasting learnable imagery, a D'Arcy machine
would expand the chapters of the Book of Life Project and give us an
interplanetary version of D'Arcy Thompson's classic "On Growth and
Form."Computers with artificial intelligence using neural networks provide
more opportunities to answer complex astrobiology imaging questions. The
non-linear evolution of artificial intelligence is customized to handle
the learning of multiple patterns or images. Computers with artificial
intelligence could accommodate various influencing variables (such as
gravity) that change over scales much larger than a linear variance can
include. Changes in the effects of gravity on a body can occur, for
instance, when humans go into outer space. Astronauts often experience
fluid retention, excessive bone loss and muscle wasting due to the effects
of microgravity. The neural network at Marshall will be able to rapidly
process the complex computations necessary for mathematically analyzing
the shapes of life (morphometrics). If someone continuously used a hand
calculator to tabulate just linear connections, at a rate of one
calculation per second it would take forty years to finish a billion
calculations. The Linux-based computer at Marshall speeds up this process
dramatically, processing over a billion connections per second.
Writing the Interplanetary Book
of LifeThe powerful capabilities of a D'Arcy classification machine could
also be used to study and catalogue images from the 14 known Martian
meteorites. The total mass to be scanned exceeds 20 kilograms (44 lbs.),
so if micron scale images are included in future projects (1 micron is
1-millionth of a meter, or 1/25,000 of an inch) the combined image
handling capabilities for biogenic classification will exceed several
trillion frames." Looking for life forms in Mars rocks means analyzing
microfossils - like potential nanometer-size - so small that 50,000 could
fit across the width of a single strand of human hair," says Noever. Based
on past performance, the Antarctic meteorite (ANSMET) field teams are
likely to recover at least 1,000 meteorites over the next three years.
Although it is likely that only a small fraction of these meteorites will
be of interest scientifically, already AMNSET has discovered 28 meteorites
that are often sampled for study. Since 1976, 301 individual investigators
representing 24 nations have received more than 10,800 meteorite samples.
To put this scale of computer acquisition and search in context, compare
it to the challenge of creating the 1996 animated feature "Toy Story." It
took nearly 3 hours for a supercomputer to process each one of that film's
140,000 frames. The challenge of classifying images of life forms
constitutes a task exceeding the creation of more than 10,000 high quality
computer-animated films.
Life is not an easy thing to
define. Even now, we're finding life forms on Earth that we never before
thought possible. Extremeophiles (bacteria that live in extreme
environments) have recently been found living in hydrothermal vents and in
high salt environments - areas once thought to be completely inhospitable
to life. In 1997, Stephen Zinder of Cornell University discovered the
existence of bacteria that thrive in the harsh solvents perchloroethylene
and trichloroethylene that are used to clean machine parts. An acid-loving
bacteria, Sulfolobus acidocaldarius, can live under conditions that would
dissolve human skin in seconds.By using a D'Arcy machine to begin a
morphometric study of microbial life on Earth, someday remote and
automated instruments may be able to identify life elsewhere in the
universe - whatever form that life may take.
The Book of Life has Many
Signatures
There are many details that make
up the answer to the question, "What is life?" The following is an
abbreviated list of some of the basic properties of life on
Earth:Symmetries: Bilateral, asymmetry, posterior/anterior, radial
(jellyfish, starfish), internal/external (humans have external symmetry
but internal organs are not all symmetrical)...Appendages: amoebic
extendable, ciliated (with brush-like sweeping motions), attachment pods,
flagella tail (for forward propulsion)...Behaviors: locomotion or
propulsion (dependent on gravity, fluid/gas environment, pressure),
metabolic (feeding and respiration), methods of communication, avoidance
of death...Nervous systems: diffuse (invertebrates), central nerve ring
(starfish), dorsal nerve cord (vertebrates)...Sensitivity to light
(sight): infrared (snakes), ultraviolet (moths, bees), polarized light
(octopus)...Sensory perception for motion, temperature, position, gases
(such as oxygen or carbon dioxide), certain chemicals, vibrations and
electricity vary widely among organisms. Some sense perceptions seem to
operate in a collective or cooperative manner, as in the case of army
ants, termites, or bees, where group intelligence is greater than the
knowledge of the single organism.
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