Lynn Margulis, a biologist whose work on the origin of cells
helped transform the study of evolution, died on Tuesday at her home in Amherst,
Mass. She was 73.
She died five days after suffering a hemorrhagic stroke, said Dorion Sagan, a
son she had with her first husband, the cosmologist Carl Sagan.
Dr. Margulis, who had the title of distinguished university professor of
geosciences at the University of Massachusetts, Amherst, since 1988, drew upon
earlier, ridiculed ideas when she first promulgated her theory, in the late
1960s, that cells with nuclei, which are known as eukaryotes and include all the
cells in the human body, evolved as a result of symbiotic relationships among
bacteria.
The hypothesis was a direct challenge to the prevailing neo-Darwinist belief
that the primary evolutionary mechanism was random mutation.
Rather, Dr. Margulis argued that a more important mechanism was symbiosis; that
is, evolution is a function of organisms that are mutually beneficial growing
together to become one and reproducing. The theory undermined significant
precepts of the study of evolution, underscoring the idea that evolution began
at the level of micro-organisms long before it would be visible at the level of
species.
“She talked a lot about the importance of micro-organisms,” said her daughter,
Jennifer Margulis. “She called herself a spokesperson for the microcosm.”
The manuscript in which Dr. Margulis first presented her findings was rejected
by 15 journals before being published in 1967 by the Journal of Theoretical
Biology. An expanded version, with additional evidence to support the theory —
which was known as the serial endosymbiotic theory — became her first book,
“Origin of Eukaryotic Cells.”
A revised version, “Symbiosis in Cell Evolution,” followed in 1981, and though
it challenged the presumptions of many prominent scientists, it has since become
accepted evolutionary doctrine.
“Evolutionists have been preoccupied with the history of animal life in the last
500 million years,” Dr. Margulis wrote in 1995. “But we now know that life
itself evolved much earlier than that. The fossil record begins nearly 4,000
million years ago! Until the 1960s, scientists ignored fossil evidence for the
evolution of life, because it was uninterpretable.
“I work in evolutionary biology, but with cells and micro-organisms. Richard
Dawkins, John Maynard Smith, George Williams, Richard Lewontin, Niles Eldredge
and Stephen Jay Gould all come out of the zoological tradition, which suggests
to me that, in the words of our colleague Simon Robson, they deal with a data
set some three billion years out of date.”
Lynn Petra Alexander was born on March 5, 1938, in Chicago, where she grew up in
a tough neighborhood on the South Side. Her father was a lawyer and a
businessman. Precocious, she graduated at 18 from the University of Chicago,
where she met Dr. Sagan as they passed each other on a stairway.
She earned a master’s degree in genetics and zoology from the University of
Wisconsin and a Ph.D. in genetics from the University of California, Berkeley.
Before joining the faculty at Massachusetts, she taught for 22 years at Boston
University.
Dr. Margulis was also known, somewhat controversially, as a collaborator with
and supporter of James E. Lovelock, whose Gaia theory states that Earth itself —
its atmosphere, the geology and the organisms that inhabit it — is a
self-regulating system, maintaining the conditions that allow its perpetuation.
In other words, it is something of a living organism in and of itself.
Dr. Margulis’s marriage to Dr. Sagan ended in divorce, as did a marriage to
Thomas N. Margulis, a chemist. Dr. Sagan died in 1996.
In addition to her daughter and her son Dorion, a science writer with whom she
sometimes collaborated, she is survived by two other sons, Jeremy Sagan and
Zachary Margulis-Ohnuma; three sisters, Joan Glashow, Sharon Kleitman and Diane
Alexander; two half-brothers, Robert and Mark Alexander; a half-sister, Sara
Alexander; and nine grandchildren.
“More than 99.99 percent of the species that have ever existed have become
extinct,” Dr. Margulis and Dorion Sagan wrote in “Microcosmos,” a 1986 book that
traced, in readable language, the history of evolution over four billion years,
“but the planetary patina, with its army of cells, has continued for more than
three billion years. And the basis of the patina, past, present and future, is
the microcosm — trillions of communicating, evolving microbes.”
The genome pioneer J. Craig Venter has taken another step in his quest to
create synthetic life, by synthesizing an entire bacterial genome and using it
to take over a cell.
Dr. Venter calls the result a “synthetic cell” and is presenting the research as
a landmark achievement that will open the way to creating useful microbes from
scratch to make products like vaccines and biofuels. At a press conference
Thursday, Dr. Venter described the converted cell as “the first self-replicating
species we’ve had on the planet whose parent is a computer.”
“This is a philosophical advance as much as a technical advance,” he said,
suggesting that the “synthetic cell” raised new questions about the nature of
life
Other scientists agree that he has achieved a technical feat in synthesizing the
largest piece of DNA so far — a million units in length — and in making it
accurate enough to substitute for the cell’s own DNA.
But some regard this approach as unpromising because it will take years to
design new organisms, and meanwhile progress toward making biofuels is already
being achieved with conventional genetic engineering approaches in which
existing organisms are modified a few genes at a time.
Dr. Venter’s aim is to achieve total control over a bacterium’s genome, first by
synthesizing its DNA in a laboratory and then by designing a new genome stripped
of many natural functions and equipped with new genes that govern production of
useful chemicals.
“It’s very powerful to be able to reconstruct and own every letter in a genome
because that means you can put in different genes,” said Gerald Joyce, a
biologist at the Scripps Research Institute in La Jolla, Calif.
In response to the scientific report, President Obama asked the White House
bioethics commission on Thursday to complete a study of the issues raised by
synthetic biology within six months and report back to him on its findings. He
said the new development raised “genuine concerns,” though he did not specify
them further.
Dr. Venter took a first step toward this goal three years ago, showing that the
natural DNA from one bacterium could be inserted into another and that it would
take over the host cell’s operation. Last year, his team synthesized a piece of
DNA with 1,080,000 bases, the chemical units of which DNA is composed.
In a final step, a team led by Daniel G. Gibson, Hamilton O. Smith and Dr.
Venter report in Thursday’s issue of the journal Science that the synthetic DNA
takes over a bacterial cell just as the natural DNA did, making the cell
generate the proteins specified by the new DNA’s genetic information in
preference to those of its own genome.
The team ordered pieces of DNA 1,000 units in length from Blue Heron, a company
that specializes in synthesizing DNA, and developed a technique for assembling
the shorter lengths into a complete genome. The cost of the project was $40
million, most of it paid for by Synthetic Genomics, a company Dr. Venter
founded.
But the bacterium used by the Venter group is unsuitable for biofuel production,
and Dr. Venter said he would move to different organisms. Synthetic Genomics has
a contract from Exxon to generate biofuels from algae. Exxon is prepared to
spend up to $600 million if all its milestones are met. Dr. Venter said he would
try to build “an entire algae genome so we can vary the 50 to 60 different
parameters for algae growth to make superproductive organisms.”
On his yacht trips round the world, Dr. Venter has analyzed the DNA of the many
microbes in seawater and now has a library of about 40 million genes, mostly
from algae. These genes will be a resource to make captive algae produce useful
chemicals, he said.
Some other scientists said that aside from assembling a large piece of DNA, Dr.
Venter has not broken new ground. “To my mind Craig has somewhat overplayed the
importance of this,” said David Baltimore, a geneticist at Caltech. He described
the result as “a technical tour de force,” a matter of scale rather than a
scientific breakthrough.
“He has not created life, only mimicked it,” Dr. Baltimore said.
Dr. Venter’s approach “is not necessarily on the path” to produce useful
microorganisms, said George Church, a genome researcher at Harvard Medical
School. Leroy Hood, of the Institute for Systems Biology in Seattle, described
Dr. Venter’s report as “glitzy” but said lower-level genes and networks had to
be understood first before it would be worth trying to design whole organisms
from scratch.
In 2002 Eckard Wimmer, of the State University of New York at Stony Brook,
synthesized the genome of the polio virus. The genome constructed a live polio
virus that infected and killed mice. Dr. Venter’s work on the bacterium is
similar in principle, except that the polio virus genome is only 7,500 units in
length, and the bacteria’s genome is more than 100 times longer.
Friends of the Earth, an environmental group, denounced the synthetic genome as
“dangerous new technology,” saying that “Mr. Venter should stop all further
research until sufficient regulations are in place.”
The genome Dr. Venter synthesized is copied from a natural bacterium that
infects goats. He said that before copying the DNA, he excised 14 genes likely
to be pathogenic, so the new bacterium, even if it escaped, would be unlikely to
cause goats harm.
Dr. Venter’s assertion that he has created a “synthetic cell” has alarmed people
who think that means he has created a new life form or an artificial cell. “Of
course that’s not right — its ancestor is a biological life form,” said Dr.
Joyce of Scripps.
Dr. Venter copied the DNA from one species of bacteria and inserted it into
another. The second bacteria made all the proteins and organelles in the
so-called “synthetic cell,” by following the specifications implicit in the
structure of the inserted DNA.
“My worry is that some people are going to draw the conclusion that they have
created a new life form,” said Jim Collins, a bioengineer at Boston University.
“What they have created is an organism with a synthesized natural genome. But it
doesn’t represent the creation of life from scratch or the creation of a new
life form,” he said.
DALLAS (AP) — A Dallas man
who spent more than 27 years in prison for a murder he didn't commit was freed
Tuesday, after being incarcerated longer than any other wrongfully convicted
U.S. inmate cleared by DNA testing.
James Lee Woodard stepped
out of the courtroom and raised his arms to a throng of photographers.
Supporters and other people gathered outside the court erupted in applause.
"No words can express what a tragic story yours is," state District Judge Mark
Stoltz told Woodard at a brief hearing before his release.
Woodard, cleared of the 1980 murder of his girlfriend, became the 18th person in
Dallas County to have his conviction cast aside. That's a figure unmatched by
any county nationally, according to the Innocence Project, a New York-based
legal center that specializes in overturning wrongful convictions.
"I thank God for the existence of the Innocence Project," Woodard, 55, told the
court. "Without that, I wouldn't be here today. I would be wasting away in
prison."
Overall, 31 people have been formally exonerated through DNA testing in Texas,
also a national high. That does not include Woodard and at least three others
whose exonerations will not become official until Gov. Rick Perry grants pardons
or the Texas Court of Criminal Appeals formally accepts the ruling of lower
courts that have already recommended exoneration.
Woodard was sentenced to life in prison in July 1981 for the murder of a
21-year-old Dallas woman found raped and strangled near the banks of the Trinity
River.
He was convicted primarily on the basis of testimony from two eyewitnesses, said
Natalie Roetzel, the executive director of the Innocence Project of Texas. One
has since recanted in an affidavit. As for the other, "we don't believe her
testimony was accurate," Roetzel said.
Like nearly all the exonorees, Woodard has maintained his innocence throughout
his time in prison. But after filing six writs with an appeals court, plus two
requests for DNA testing, his pleas of innocence became so repetitive and
routine that "the courthouse doors were eventually closed to him and he was
labeled a writ abuser," Roetzel said.
"On the first day he was arrested, he told the world he was innocent ... and
nobody listened," Jeff Blackburn, chief counsel for the Innocence Project of
Texas, said during Tuesday's hearing.
He even stopped attending his parole hearings because gaining his release would
have meant confessing to a crime he didn't do.
"It says a lot about your character that you were more interested in the truth
than your freedom," the judge told Woodard after making his ruling.
Blackburn and prosecutors hailed Tuesday's hearing as a landmark moment of
frequent adversaries working together.
Since the DNA evidence was tied to rape and Woodard was convicted of murder,
Innocence Project attorneys had to prove that the same person committed both
crimes. They said they couldn't have done that without access to evidence
provided by Dallas County District Attorney Craig Watkins' office.
"You've got to have very good lawyers with a lot of experience and skill ...
working on both ends of this case, hard," Blackburn said. "And you've also got
to have government power behind what you do."
Under Watkins, Dallas County has a program supervised by the Innocence Project
of Texas that is reviewing hundreds of cases of convicts who have requested DNA
testing to prove their innocence.
While the number of exonerations on Watkins' watch continues to grow, he said
this one was a little different.
"I saw the human side of it, and seeing the human said of it just gives you more
courage to advocate for issues like this," said Watkins, who had breakfast with
Woodard on Tuesday morning. "It gives me that resolve to go even further to find
out who (the killer) is so that we can get him into custody."
Woodard said his family was "small and scattered," although he pointed out a
niece in the courtroom. He said his biggest regret was not being with his mother
when she died.
"I can tell you what I'd like to do first: breathe fresh, free air," Woodard
said during a news conference in the courtroom after the hearing. "I don't know
what to expect. I haven't been in Dallas since buses were blue."
We are fast approaching Father’s Day, the festive occasion on
which we plague Dad with yet another necktie or collect phone call and just
generally strive to remind the big guy of the central verity of paternity — that
it’s a lot more fun to become a father than to be one. “I won’t lie to you,”
said the great Homer Simpson. “Fatherhood isn’t easy like motherhood.” Yet in
our insistence that men are more than elaborately engineered gamete vectors, we
neglect the marvels of their elaborately engineered gametes. As the scientists
who study male germ cells will readily attest, sperm are some of the most
extraordinary cells of the body, a triumph of efficient packaging, sleek design
and superspecialization. Human sperm are extremely compact, and they’ve been
stripped of a normal cell’s protein-making machinery; but when cast into the
forbidding environment of the female reproductive tract, they will learn on the
job and change their search strategies and swim strokes as needed.
Sperm are also fast and as cute as tadpoles. They have chubby teardrop heads and
stylish, tapering tails, and they glide, slither, bumble and do figure-eights.
So while a father may not be entitled to take the same pride in his sperm as he
does in his kids, it’s fair to celebrate the single-minded cellular commas that
helped give those children their start.
Sperm are pretty much the tiniest cells in the human body. The head of a mature,
semen-ready sperm cell spans about 5 microns, or two-thousandths of an inch,
less than half the width of a white blood cell or a skin cell. And a sperm cell
is absurdly dwarfed by its female counterpart, the egg, which, fittingly or not,
is among the biggest cells in the body. At 30 times the width of a sperm, the
egg is massive enough to be seen with the naked eye.
But men have the overwhelming quantitative edge in the gamete games. Whereas
current evidence suggests that a human female is born with all the eggs she will
have, and that only about 500 of her natal stock of one million will ever ripen
and have a shot at fertilization, a male from puberty onward is pretty much a
nonstop sperm bakery. Each testicle generates more than 4 million new sperm per
hour, for a lifetime total of maybe 12 trillion sperm per man (although the
numbers vary with the day and generally slope downward with age).
The average ejaculation consists mostly of a teaspoon’s worth of nonspermic
seminal fluid, a viscous mix of sugars, citric acid and other ingredients
designed to pamper and power the sperm cells and prepare them for difficult
times ahead; the sperm proper account for only about 1 percent of the semen
mass. Yet in that 1 percent may be found 150 million sperm, 150 million human
aspirants yearning to meet their mammoth other halves.
To which one can crack, dream on. Not only are there far too few eggs to go
around, but also the majority of sperm couldn’t fertilize an ovum if it were
plunked down in front of them. “Only a perfectly normal sperm can penetrate an
egg,” said Dr. Harry Fisch, a urologist at Columbia University Medical Center,
“and the majority of sperm are abnormally shaped.” Some may have pinheads,
others have two heads, some lack tails, a third don’t move at all. As a rule,
Dr. Fisch said, a man is lucky if 15 percent of his sperm are serviceable. “One
guy I saw had 22 percent,” he said, “but that’s rare.”
Creating sperm is a complex, multistep operation in which immature cells spend
one or two months wending through a labyrinth of tubules coiled in the testes,
at each stage losing a bit more of the blobby contours and yolky contents of
standard cells and assuming the streamlined profile of sperm cells. The
operation is a delicate one that must be performed at temperatures some 2
degrees below that of the body, which is why the testicles hang outside the
body, where breezes can keep them cool; why a man hoping to become a father is
advised to skip the hot baths and saunas; and why a bout of high fever can
disrupt fertility for months.
The model sperm that emerges at tubule’s end has, like an insect, three basic
body segments. Of crowning importance is the head, which is taken up largely by
a supercondensed tangle of 23 chromosomes, half the complement of DNA found in a
normal body cell and thus the right number to merge with an egg’s 23 chromosomes
and begin tapping out a whole new body. At the tip of the sperm head is the
acrosome, a specialized sack of enzymes that help the sperm penetrate through
what Joseph S. Tash, a male fertility expert at the University of Kansas Medical
Center, calls the “forest” of ancillary cells and connective tissue that
surrounds the ripe, ready egg.
Below the head is the midpiece, which is packed with the tiny engines called
mitochondria that lend the sperm its motility, and below the midpiece is the
tail, a bundle of 11 entwined filaments that thrashes and propels a sperm
forward at the estimable pace of one-twelfth of an inch per minute, the
equivalent of a human striding at four miles an hour.
Sperm do not really hit their stride until they are deposited in the female
reproductive tract, at which point chemical signals from the vaginal and
cervical mucus seem to spark them to life. Released from the buffering folds of
their seminal delivery blanket, they at first swim straight ahead,
torpedo-style, “with very little back and forth of the head,” Dr. Tash said.
They may linger in the cervical mucus for a couple of days, or cross the cervix
and enter the uterus.
If an egg has burst from its ovarian follicle and been plucked by a fallopian
tube, sperm can sense its signature, a telltale shift in calcium ions. The sperm
become “hyperactivated,” said Moira O’Bryan, a sperm expert at Monash University
in Australia, switching to “a crazed figure-eight motion” ideal for boring
through barriers. The ovum eggs them on, signaling some to play the sacrificial
kamikaze and explode their enzyme sacks prematurely, loosening the corridor for
other, shapelier sperm to pass through intact. A few dozen fine-figured sperm
find their way to the final barrier, the egg’s plasma membrane, where they
waggle with all their crazy-eight might and beg to be chosen — but only one will
be taken, will fuse with the egg and be absorbed into its rich inner sanctum.
In a fraction of a second, an electrical, ionic jolt dramatically changes the
egg’s outer coat, to forestall the lethal intrusion of additional sperm.
The wheels are in motion. How do you like your new tie?
