Francis H.C. Crick, 88, co-discoverer of one of the most important scientific findings of the 20th century, the recognition of the double helix structure of DNA as the blueprint of life, died Wednesday at San Diego's Thornton Hospital. He had colon cancer.

Crick's powerful intellect and willingness to cross the boundaries of scientific disciplines led him and colleague James D. Watson to understand the "twisted ladder" structure of deoxyribonucleic acid, or DNA, which carries information about heredity. What they learned was that each strand of the double helix could become a template for copying an organism's genes, and that replication is the way that every living cell has been created.

After that discovery in 1953, scientific understanding leapfrogged previously insurmountable barriers, ultimately giving birth to the $30 billion-a-year biotechnology industry. Scientists also placed human genes in bacteria to create new drugs and vaccines. They manipulated plant genes to resist disease, used bits of stray DNA to identify criminals, and improved couples' chances of having babies. The discovery helped scientists understand how humans inherit traits and how that system of inheritance further explains evolution.

Crick's work with Watson on the double helix structure, and his subsequent work firming up the foundations of molecular biology, made him a seminal scientific figure.

"He is a giant," said Francis Collins, director of the National Human Genome Research Institute, at the National Institutes of Health. "It's fair to say Francis Crick defined the discipline of theoretical biology, and so far no other practitioners of that art have come up to that standard."

Richard A. Murphy, president and chief executive of the Salk Institute, Crick's research base for the past 28 years, said, "Francis Crick will be remembered as one of the most brilliant and influential scientists of all time."

Stanford University scientist Paul Berg, who won the Nobel Prize in chemistry in 1980 for his genetic engineering work, said in a statement to the Associated Press, "It's almost too difficult to pay him high enough tribute for what he contributed." The news of the double helix discovery was published May 23, 1953, in the British journal Nature, but it was several weeks before the world noticed. Perhaps it was because Crick and Watson so simply understated the conclusion: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."

However circumspect he was in print, the British-born Crick was more certain in person. Watson wrote in his 1968 book, "The Double Helix," that Crick walked into the dingy English pub where they habitually lunched and loudly announced that they had found the secret to life. Crick's wife, Odile Speed, said he made the same announcement to her, but she disregarded it because he was always coming home and saying things like that.

In 1962, Crick, Watson and Maurice Wilkins received the Nobel Prize in medicine for their work at the Cavendish Laboratory at the University of Cambridge. Rosalind Franklin, who also worked on the research, died in 1958 before the Nobel was awarded. It is not awarded posthumously.

Unlike many biologists, Crick and Watson did not conduct experiments. Their technique was thinking, arguing and thinking some more. Watson's sister typed the manuscript for their Nature article. The scientists didn't even build the final model of the double helix, leaving that to Crick's wife, an artist who principally painted nudes.

Crick spent the next 13 years building on the discovery. Crick and Watson suggested a general theory for the structure of small viruses. Crick and Sydney Brenner from the University of Cambridge accurately proposed the existence of small chemicals known as "adapters" that are needed to assemble proteins, one amino acid at a time, from genetic instructions. Crick postulated that it would take three letters of the DNA code to describe amino acids. He made discoveries about the ways in which genes are damaged by certain chemicals.

"No one man created molecular biology. But one man dominates intellectually the whole field because he knows and understands the most: Francis Crick," said the late Jacques Monod, a French Nobel Prize winner.

After incredible work on biology at the molecular level, Crick "decided to attack something really hard," Collins noted. "The mind and the brain."

The nature of consciousness is a solvable, if complex, problem, Crick argued. The human body contains tens of millions of neurons, including in the stomach and intestines. "When you digest your lunch, is that you?" Crick asked in an interview last year. "People think the brain is mysterious but not the weather. Why is that?" The brain may be less enigmatic than the weather, he said, because "we don't yet have a clear understanding of how raindrops form but we do know how individual neurons and synapses work."

His later work was not without its critics, although supporters insist that Crick, true to the scientific method, was simply following questions where they led and posing hypotheses. He suggested that Sigmund Freud was wrong about dreams and that they were simply the result of "cerebral housecleaning" so the memory could store information more efficiently. In other words, "we dream in order to forget."

His 1981 book, "Life Itself," postulated that life began on Earth when microorganisms wafted in from spacecraft. The hypothesis, Crick noted, makes the strong prediction that "the earliest organisms should appear suddenly, without any sign of any precursors here on Earth." That is what the fossil record shows. But many scientists noted that the fossil record is incomplete and that the earliest life forms might have been too small and fragile to be preserved.

Crick later said that writing the book was probably a mistake because inattentive readers got the idea that "I was a bit nutty."

"The important thing is that you have lots of ideas and that you learn most are going to be wrong," he told an interviewer. "The trick is to figure out which are the most promising and work on those."

In his 1994 book, "The Astonishing Hypothesis,'' he outlined an empirical approach focusing on visual consciousness, something that would lead to the death of the soul. "You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules.''

"In the fullness of time,'' he continued, "educated people will believe there is no soul independent of the body, and hence no life after death.''

Francis Harry Compton Crick was born in Northampton, England. His parents bought the inquisitive boy a "Children's Encyclopedia," which answered many questions for him, although he told his mother that he worried that by the time he grew up, "everything was going to be discovered."

He attended University College in London, receiving a bachelor's degree in physics in 1937. His graduate work was interrupted by World War II, in which he served as a scientist for the British Admiralty, working on magnetic and acoustic underwater mines.

He knew no biology and practically no organic chemistry or crystallography, so he spent the postwar years learning those disciplines. He was a 33-year-old doctoral student, working at the Cavendish Laboratory in 1951, investigating the structure of proteins, when he met the 23-year-old American Watson.

"I will always remember Francis for his extraordinarily focused intelligence and for the many ways he showed me kindness and developed my self-confidence," Watson said in a written statement yesterday. "For two years I was almost a family member, the much younger brother prone to intellectually stray. Sharing with him our office . . . was an extraordinary privilege. Until his death, Francis was the person with whom I could most easily talk about ideas."

Crick did not welcome the attention the Nobel brought, nor did he like the limelight from Watson's best-selling "The Double Helix." In person, colleagues said, he was quick-witted and charming. But he refused to sit for most interviews or to travel to most award ceremonies or commemorations.

"He was not about to be distracted by the fact that he was a legend," Collins said, calling him intellectually fearless. He was also known for responding to requests for his time or donations with a preprinted postcard, with one of 13 boxes checked off that said he could not send an autograph, appear for an award, donate his time and the like.

Crick worked at Cambridge until 1977, and then moved to a wood-lined office overlooking the Pacific at the Salk Institute in La Jolla, Calif.

His seven-year marriage to Ruth Doreen Dodd ended in divorce.

Survivors include his wife of 54 years of La Jolla, a son from his first marriage, Michael F.C. Crick of Seattle; two daughters from his second marriage, Gabrielle A. Crick and Jacqueline M.T. Crick, both of England; and four grandchildren.

Francis Crick was praised as "a giant" for his findings and subsequent scientific work.Francis H.C. Crick, left, and James Watson, co-discoverers of the double helix structure of DNA, pose in Cambridge in an undated photo.