FOR Marina Silva, life began in the heart of the Amazon. From the age of 11, she walked nine miles a day helping her father collect rubber from trees.
These days, as an icon in the environmental movement, she has dedicated her life to protecting that same rainforest.
Illiterate and seriously ill from hepatitis, Ms. Silva left her home when she was 16 and headed by bus to the city of Rio Branco seeking medical care and an education. There she learned how to read and write, graduated from college and became a teacher and a politician.
She worked closely with her friend Chico Mendes, the rubber tapper and environmental activist, before he was gunned down in 1988 by ranchers opposed to his activism. When Luiz Inácio Lula da Silva was elected Brazil’s president in 2002, he picked Ms. Silva to be his environmental minister, and on her watch Brazil devised a national plan to combat deforestation and created an indigenous reserve roughly the size of Texas.
Last week Ms. Silva shook up Brazilian politics by announcing that, after nearly three decades, she was leaving Mr. da Silva’s Workers’ Party to join the Green Party, where she is likely to be its candidate in next year’s presidential election.
Her story — that of a humble woman who overcame extreme poverty and illness to become a force in Brazilian politics — could prove an inspiration to Brazilians in their search for a president to replace the popular Mr. da Silva, himself a product of humble beginnings, political analysts said.
“Marina is a person that earned her own wings, and it is not surprising to discover that those who have wings can fly,” said Jorge Viana, the former governor of Acre, Ms. Silva’s home state.
Her candidacy would pit her against Dilma Rousseff, President da Silva’s chief of staff and his choice to succeed him. Political analysts say the two women have been at odds since 2003 over the country’s economic development policy, including energy projects that Ms. Silva has questioned for environmental reasons.
Ms. Silva has “shaken up the race, mixed up all the cards,” said David Fleischer, a political science professor at the University of Brasília.
If either woman wins, history will be made. Brazil has never had a woman as president. In addition, the country has never had a black president; Ms. Silva is black.
Ms. Silva resigned as environmental minister last year, after expressing concerns that the government might give in to pressure from business interests to ease off emergency measures she put in place to counteract a jump in Amazon deforestation. She returned to the national Senate, where she continued to press her environmental agenda.
IN an interview here, Ms. Silva, 51, said she grew frustrated with the internal struggle to persuade members of the Workers’ Party to pursue a more sustainable economic development strategy.
“With the opportunity to try to construct this new future for Brazil and for the planet, I prefer to put my hopes in this movement,” she said of her switch to the Green Party.
While many admire her, some political analysts say they believe that Ms. Silva’s past serious health problems could become a political liability in a presidential contest. Hepatitis, malaria and heavy metals contamination have caused her to be hospitalized for long stretches.
Concerns about Ms. Rousseff’s chemotherapy treatment for a melanoma have dogged her in recent months and led some supporters of Mr. da Silva to urge him to back a different candidate for his successor. Brazilians still remember the case of Tancredo Neves, a popular president-elect who became severely ill in 1985 and died before taking office.
Still, Ms. Silva has spent a lifetime proving doubters wrong.
BORN in Seringal Bagaço, a small community of rubber tappers in Acre, Ms. Silva was one of 11 children, three of whom died. The family’s nearest neighbor lived about an hour away on foot through the thick forest. Reaching Rio Branco, about 43 miles away, sometimes took a week during the rainy season, when the family car would get stuck in the muddy road, she said.
Disease was common in the Amazon, and it took its toll on her family. Her mother died when Ms. Silva was 11. Two younger sisters later died with measles and malaria.
At 11, she began working with her father as a rubber tapper. They would typically leave the house at 5 a.m. and return about 12 hours later. To increase the family’s productivity, her father would go to one area of the forest and she and her sisters to another.
To keep her from being robbed or tricked by rubber buyers, her father taught her simple mathematics at an early age, she said.
After Ms. Silva became ill with hepatitis, she resolved to head to Rio Branco to find treatment. She wanted to become a nun and study.
She enrolled in a course for illiterate adults, worked as a maid and soon finished primary school. During vacation breaks, she returned to her father’s home and helped him collect rubber.
She dropped her idea of becoming a nun and entered college, graduating at 26 with a history degree.
While at the university, she joined the Revolutionary Communist Party, a clandestine group working to oppose Brazil’s military dictatorship.
During that period, she met Mr. Mendes, a rubber tapper who organized workers to warn about the dangers of burning and clearing the forest and about the displacement of traditional Amazon communities.
Ms. Silva joined Mr. Mendes’s movement, which involved peaceful demonstrations, and it led her into politics. After being elected a town councilwoman in Rio Branco, she went on to become a state legislator and a federal senator.
With her staunch advocacy of the Amazon, Ms. Silva “was clearly the candidate of the Brazilian environmental movement,” said Steve Schwartzman, the director of tropical forest policy at Environmental Defense Fund in Washington and a longtime friend.
“Marina was part of the movement that made the Amazon and deforestation and the possibility of a different development model a national issue in Brazil in a way it had never been before,” he said.
Her advocacy won her acclaim from international environmental groups around the world, which say that clearing of the forest for Brazilian industries could be affecting global climate change. Although deforestation continues, the rate slowed significantly from 2004 to 2007.
But in May 2008 Ms. Silva resigned her position, blaming “stagnation” within the government on its environmental policy. She had become increasingly isolated in Mr. da Silva’s government over her criticism of some proposed hydroelectric dams and of genetically modified crops.
STILL, most of the policies she set in motion have continued, environmentalists said.
She credited Mr. da Silva, whom she considers a “living hero” along with Nelson Mandela and Barack Obama, for Brazil’s progress on protecting the environment. But she said the government must preserve the advances it had made.
“I was fortunate to achieve some things, but they were far short of what Brazil and the world needs us to do,” she said.