What came first, the chicken or the egg?
(Top Posts - Science - 053002)

Simple but misleading question in that neither is an
end or a beginning, alone, both requiring other parts
for continuance and for existence, all parts existing
in a long-lived continuum. A lengthy answer entailing
how the chicken and the egg arrived on the scene ...

Details on requisite matter / chemistry for existence
(most of the symbiotic facts of nature entailing the man-
ner in which many life forms in the environment interact
to make life possible) skipped to get to the core of the
chicken or egg question:

The chicken hen contains eggs and the chicken rooster
contains sperm. Each chicken egg within the chicken hen
is potentially a chicken hen or a rooster, neither of which
alone is able to reproduce but which, upon mating and
fertilization by a chicken hen and rooster, may produce
more chicken eggs and ___ (repeat aforementioned steps).

Note, most fertilized eggs don't make it to live birth, either
by act of nature or humans, so a lot of the reproduction
process entails non-procreative fertilizations and non-fertil-
azations.

All sexual life was descended from what was once asexual
life. Asexual life is still prevalent on the globe.

---
Scientists Explore the Why of Sex
http://www.msnbc.com/news/705437.asp?0dm=C12OH
February 13, 2002
---

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}}}} How mixing genes keeps species sound {{{{

Birds do it, bees do it -- even fruit flies do it. Scientists
are studying fruit flies to see precisely how sexual repro-
duction benefits the species

.... it's so widespread among plants and animals that there
must be some payoff. After more than a half-century of
debate and 20 published theories, scientists are still trying
to pin down just what the payoff is.

.... It is easy to forget that sex is not the only game in town
for the plant and animal kingdoms. In fact, there are thous-
ands of asexual species now.

.... It's inefficient and genetically unpredictable. So what's
the appeal of sex, biologically speaking? Most of the world's
species reproduce sexually, but some carry out nature's
orders without a mate.

.... it is rare for an asexual species to persist a very long time
in evolutionary terms, suggesting again there's something
beneficial about sex.

Yet, at first blush, it makes some sense to have self-repro-
ducing females and just dispense with males altogether,
even before you consider things like singles bars. After
all, if your job is to pass on your genes to future gener-
ations -- and according to evolutionary biology, that is
your job -- sex just gets in the way.

Consider the notion of two mating sexes. Each female
passes only half her genes to each offspring, rather than
all of them. And about half her brood on average ends up
without a womb, which chops the next generation's pro-
ductive capacity in half.

What's more, sex breaks up the successful gene combin-
ations found in the parents and gambles on new, untried
mixes in the next generation. Does that make any sense?

Maybe so. It's pretty clear, scientists say, that the evolu-
tionary lure of sex has something to do with that gene-mix-
ing. While clones merely pass along their genetic endow-
ment in a chunk, sexual species shuffle the deck.

To understand that, remember that the genetic makeup
of an organism is somewhat like a baseball team. Every-
body has a full team, with all the positions covered, but
who plays at each spot differs. And there are good
players and bad players in the same way there are good
genes and bad genes.

Clones essentially pass their own rosters on to their off-
spring, while sexual species create new rosters.

.... Why tinker with a successful genetic lineup?

Currently, most scientists offer two general theories
about why sex is so good: It helps a species get rid of
harmful mutated genes, or, alternatively, it helps the
population take advantage of beneficial mutations. Call
it bad genes vs. good genes.

Of course, the explanation could be some combination
of those two ideas, although scientists suspect one or
the other is probably the major factor.

The bad-gene idea says sex can make the faulty genes
sitting ducks for elimination by natural selection, by
separating them from good genes as they pass through
generations. It can group bad genes together so they
get wiped out in batches when the unfortunate recipients
don't reproduce. Sex can also break up harmful combin-
ations of genes, even when each by itself isn't so bad.

The alternative view says sex can help good genes spread
through a species or bring favorable combinations together,
speeding up evolution and helping species adapt more
quickly to changing environments. One version says sex
helps defend populations against evolving parasites and
germs, for example.

.... it appears humans naturally produce harmful muta-
tions so often that we'd go extinct if we didn't use sex
to get rid of them. But it's not clear how often that situa-
tion occurs in other animals, and therefore how widely
the bad-mutations theory of sex can be applied.

.... Most evolutionary biologists probably favor theories
about promoting the spread of good genes rather than
those focusing on eliminating harmful mutations. ...

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The chicken hen and the chicken rooster and the chicken
hen's eggs and the chicken rooster's sperm are a result of
billions of years of evolution.

Analysis of some of the key events in the origins and
evolution of life on earth, events eventually leading to the
chicken hen, chicken rooster, chicken eggs, and chicken
sperm (all four parts required for the furtherance of the
species):

Over 12 billion years ago ...

Everything From Everlasting
Not-Quite Nothing ... (040401)
http://prohuman.net/science/everything_nothing.htm

~4.6 billion years ago ...

Formation of earth and sister planets; intense
bombardment of planet surfaces. Graphic sum-
marizing earth's evolution which originated
in a nebula from a supernova explosion:
http://www.discovery.com/exp/earthjourneys/zoom990621e.html

~4 to ~3.5 billion years ago ...

Life spark (deep sea vents?, meteorite impacts?).

Microbial life (bacteria), Stramatolites (bacterial
skyscrapers).

Hypotheses about the possibility of life's origins in
hydrothermal vents:
http://www.resa.net/nasa/ocean_hydrothermal.htm#origins

Details on current life (300 species) which resides
near hydrothermal vents:
http://www.pbs.org/wgbh/nova/abyss/life/extremes.html

Map of currently known hydrothermal vent locations:
http://www.pbs.org/wgbh/nova/abyss/frontier/vents.html

Life's First Scalding Steps (January 9, 1999):
http://www.sciencenews.org/sn_arc99/1_9_99/bob1.htm

Theories on Origin of Life on Earth:
http://ethomas.web.wesleyan.edu/ees104/lect6b.htm

How did it all begin? The self-assembly of organic
molecules and the origin of cellular life:
http://www.ucmp.berkeley.edu/education/events/deamer1.html

Life's Far-Flung Raw Materials - Life may owe its start to
complex organic molecules manufactured in the icy heart
of an interstellar cloud (July, 1999):
http://www.sciam.com/1999/0799issue/0799bernstein.html

Hitchhiking Molecules Could Have Survived Fiery Comet
Collisions With Earth, UC Berkeley Experiment Shows
(April 6, 2001)
http://www.sciencedaily.com/releases/2001/04/010406073728.htm

Life from space dust? (August 15, 2001)
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1492000/1492411.stm

Triumph of Life
http://www.pbs.org/wnet/nature/triumphoflife/

Origins of Life
http://www.resa.net/nasa/origins_life.htm

DNA From the Beginning - An animated primer on
the basics of DNA, genes, and heredity. ...
http://vector.cshl.org/dnaftb/

~3 billion years ago ...

Volcanic activity, stramatolites:
http://www.discovery.com/exp/earthjourneys/zoom990621a.html

~2.7 billion years ago ...

Spirochetes (bacterial joint ventures). Eukaryotes
(cells with a nucleus) leave evidence of their
existence in the form of steranes in shale
(August 13, 1999):
http://abcnews.go.com/sections/science/DailyNews/origins990813.html

~2.5 billion years ago ...

Atmospheric oxygen explodes as microbes
(cyanobacteria) begin to consume oxygen; Mass
extinction follows - up to 90% of bacteria that
require an absence of oxygen (anaerobic
organisms) die:
http://www.newscientist.com/hottopics/disaster/gasattack.jsp

~1.5 billion years ago ...

Sex Evolves as a Survival Strategy ...

How did sex evolve if we all started out as asexual beings?

From A Walk Through Time, From Stardust to Us, The
Evolution of Life on Earth, by Sidney Liebes, Elisabet
Sahtouris, and Brian Swimme:
http://www.amazon.com/exec/obidos/ASIN/0471317004
For most of our single-celled ancestors, repro-
duction and sex are entirely distinct. Reproduc-
tion involves making more individuals. Most
Earth organisms reproduce in single-parent
style: by fission, budding, or forming small
internal offspring cells.

Sex involves fusion of genetic material from at
least two individuals. Sex evolves as a survival
strategy.

In times of extreme stress--colds of winter,
drying summer heat--our protoctist ancestors
resort to cannibalism to survive. Some do not
totally digest their meal; they become doubled
beings and, gobbling still others to survive,
most bloat up and die.

When the environment rebounds, the survivors
need to shed their doubleness and tripleness to
avoid dying. These problem solvers evolve ways
to regularly double every winter (or dry season)
through sex, and relieve the doubling every spring.

Seasonal cycling is both a beauty and a constraint
for life on Earth. Sex originated for survival, not
for reproduction.

Study Links Origin of Sexual Reproduction With
High Mutation Rates (July 10, 2001)
http://news.nationalgeographic.com/news/2001/07/0709_sexorigin.html
Biologists have long known the advantages of
sexual reproduction to the evolution and survival
of species. Sex helps a fledgling creature pass on
its good mutations and respond better to environ-
mental stresses that would leave its asexual neigh-
bors floundering in the shallow end of the gene
pool.

But a puzzling question is, how did sex begin in
the first place?

Researchers from the California Institute of Tech-
nology (Caltech) and the Jet Propulsion Laboratory
(JPL) propose an answer, based on studies of RNA
material and computer-simulated activity of bacteria.

Claus Wilke of Caltech and Chris Adami, of both
Caltech and JPL, have concluded that asexual bac-
teria can be nudged to evolve into sexual reproduc-
tion if they are subject to high levels of mutation
induced by environmental stress—from, say, radia-
tion exposure or a catastrophic meteor.

.... "The reason the origin of sexual reproduction has
been such a big mystery is that we look at the world
as it is now. But the early world was a much more
stressful place, sometimes changing very rapidly ...
high mutation rates can, under the right conditions,
force an asexual organism to become sexual."

~700 million years ago ...

Was The Humble Sponge Earth's First Animal?
(April 1, 2002)
http://news.nationalgeographic.com/news/2002/04/
0401_0401_shapeoflife1.html

A Surprising Link - That sponges are an essential
part of our evolutionary heritage is a startling reali-
zation for many, but Sogin reached an even greater
revelation when he looked slightly farther back on
the animal lineage.

"The special evolutionary relationship between animals
and fungi was a big surprise," Sogin says. "In many
regards, fungi are similar to primitive plants." Yet the
fungus, he has concluded, shares "a unique, common
evolutionary history with the animal."

Some details of early animal evolution still remain to
be worked out. In particular, Sogin would like to know
whether certain types of fungi are more closely related
to animals than other types.

If they are, it would mean that the entire animal family
is just a branch on the evolutionary tree of the fungi.
In a sense, people—and all animals—would be highly
evolved fungi.

Another unanswered question is how some of the early
branches of the animal family tree fit together. After
sponges, Sogin thinks, jellyfish evolved, and then ane-
mones, which gave rise to the first animal with bilateral
symmetry.

Once the step toward symmetry was made, animal evo-
lution appears to have quickly gained momentum. ...

~600 million years ago ...

Evidence of small animals with soft body parts;
Precambrian mass extinction; 70 percent of flora
and fauna perish:
http://www.wf.carleton.ca/Museum/extinction/vencause.html

Keys to evolution of all life ...

Homeobox Genes (March 19, 1998):
http://www.bbc.co.uk/horizon/hopefulmonsters.shtml

Discovery of the Molecular Basis of Evolution
(November 25, 1998):
http://news.bbc.co.uk/hi/english/sci/tech/newsid_222000/222096.stm

Prions May Play Crucial Role In Evolution
(September 28, 2000):
http://www.sciencedaily.com/releases/2000/09/000928070638.htm

Teaching About Evolution and the Nature of
Science (1998):
http://www.nap.edu/readingroom/books/evolution98/evol1.html

The Evolution of Life on Earth, by Stephen Jay Gould:
http://www.geocities.com/CapeCanaveral/Lab/2948/gould.html

~540 million years ago ...

Cambrian explosion - all of today's animal phyla,
great groups, emerge including the Human
ancestors, the worms (August 25, 1997):
http://www.sciam.com/explorations/082597cambrian/powell.html

~250 million years ago ...

Permian extinction, the *largest extinction event*
in history, ~96% of marine species and ~75% of
vertebrate families disappear - causality suspects:
http://www.wf.carleton.ca/Museum/extinction/permcause.html

~230 million years ago ...

Oldest dinosaurs ever, Prosauropods who walked
the earth 225 to 230 million years ago, discovered;
the creatures had small heads and long necks and
could walk on two or four legs and they ate only
plants; their remains were found in Madagascar
(October 22, 1999):
http://news.bbc.co.uk/hi/english/sci/tech/newsid_481000/481703.stm

BBC - Walking With Dinosaurs:
http://www.bbc.co.uk/dinosaurs

~145 million years ago ...

Origins of birds (evolved from dinosaurs):

Wings for speed (May 6, 1999):
http://news.bbc.co.uk/hi/english/sci/tech/newsid_336000/336192.stm

Bones make feathers fly (August 14, 2000):
http://news.bbc.co.uk/hi/english/sci/tech/newsid_879000/879956.stm

~65 million years ago ...

Cretaceous mass extinction, the 2nd largest
extinction in history with over 85% of all families
disappearing, including most dinosaurs - causality
suspects:
http://www.bbc.co.uk/education/darwin/exfiles/asteroid1.htm
http://www.bbc.co.uk/education/darwin/exfiles/asteroid2.htm
http://www.bbc.co.uk/education/darwin/exfiles/volcano.htm

~56 million years ago ...

Origins of order of birds which includes wild ducks
and the wild jungle fowl ancestors of the modern
domesticated chicken, based on genetic studies.

~8 million years ago ...

Lineage leading to modern gorillas branched away
from remaining African ape species, the combined
chimpanzee and human line:
http://www.bbc.co.uk/science/apeman/fact_file/evolution/apes

~6 million years ago ...

Lineage leading to modern chimps, and that
leading to humans, split:
http://www.bbc.co.uk/science/apeman/fact_file/evolution/apes

~400,000 years ago ...

Recent findings indicate mitochondrial DNA research
might place the common ancestor of modern humans
approximate to this time period (March 11, 1999):
http://news.bbc.co.uk/hi/english/sci/tech/newsid%5F294000/294808.stm

~130,000 years ago ...

Homo sapiens - the 1st truly modern human, found in
Omo in Ethiopia, represents the earliest known example
of a modern human being; its skull size and shape are
completely modern:
http://www.bbc.co.uk/science/apeman/fact_file/species/modern_humans

~13,000 years ago ...

The first farmers grew wheat and rye 13,000 years
ago in Syria and were forced into cultivating crops
by a terrible drought (October 28, 1999):
http://news.bbc.co.uk/hi/english/sci/tech/newsid%5F489000/489449.stm

10,500 years ago ...

Goats domesticated from bezoar goats in the
Near East.

~10,000 years ago ...

Sheep domesticated from Asiatic moufflon in the
Near East.

~9,500 years ago ...

Pigs domesticated from wild boars in the Near East.

~9,000 years ago ...

Cattle domesticated from aurochs and cats domes-
ticated from wild cats in the Near East.

~6,400 years ago ...

Horses domesticated from tarpans in southern
Russia.

~5,250 years ago ...

Development of cuneiform in Mesopotamia.

~5,000 years ago ...

Camels domesticated from wild camels in south
central Asia and southern Arabia.

~4,000 years ago ...

Domestication of the chicken
http://www.ext.vt.edu/resources/4h/virtualfarm/
poultry/poultry_chicken.html

The domestic chicken can be traced back to four
species of wild jungle fowl from Southeast Asia.
However, the Red jungle fowl (Gallus gallus or Gallus
bankiva) is the most commonly found wild species in
the world today and is considered the main ancestor
of the domestic chicken.

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