Seymour Benzer was one of the most brilliant scientists of our era, and a father of modern neuroscience.

He is best known for his pioneering research on the structure and function of genes, discovering in the 1960s the links between genes and behaviour. But he was extraordinarily versatile, excelling in three major scientific fields: physics, molecular biology and behavioural biology.

Before Benzer, it was commonly believed that human behaviour was shaped primarily by the environment — by nurture rather than nature. Benzer showed that genes must be assigned a far bigger role and that behaviour can be dissected by studying the genes.

Benzer began his most important research in the 1950s when geneticists believed that genes were indivisible units, linked together on chromosomes like beads on a string. But Benzer theorised that each gene was made up of discrete segments that could recombine in new combinations when two individuals mated.

Such recombination is, however, very uncommon and difficult to identify, and so testing the theory was extremely difficult. Benzer worked on one of the tiniest life forms known, called a phage. Phages are minute viruses that attack bacteria and reproduce themselves very rapidly — typically about five times each minute.

In some very elegant experiments, he mated two strains of the T4 phage. Each strain had a mutation that did not allow it to grow on the bacterium Escherichia coli (E. coli) that inhabits the stomach. When he spread the offspring of the T4 phage on a cultured layer of E. coli, he saw spots where the phage had killed the E. coli.

Benzer had demonstrated that the phage offspring had inherited healthy segments of the crucial gene from each parent. His findings confirmed the theory of the Nobel prizewinners James Watson and Francis Crick, that a gene consists of many pairs, by showing that genes can be split into individual elements.

In the mid-1960s Benzer began to wonder how genes might affect behaviour. By then, he had two daughters and, as they grew up, he noticed that they developed markedly different personalities, each behaving very differently from the other. “If you have one daughter,” he said, “you don’t notice anything. But if you have a second one, you begin to wonder, ‘Are we doing things differently, or is it genetic?’ ”

To look into this question, he began to study how fruit flies behave. He and his co-workers triggered mutations in the flies by exposing them to toxins. They then looked specifically at the way in which the offspring of the fruit flies are attracted to light. They found some that did not respond to light, others that tried to fly away from it, and yet others that had different odd variations.

By breeding these mutant flies, Benzer could pinpoint the location of some of the genes responsible for these differences in behaviour. He went on to discover genes in the flies linked to memory.

His work sparked off a new field of science — behavioural biology or neurogenetics. Neurogenetists today are continuing Benzer’s work by investigating the relationships between genes and behaviour in other animals, including humans. The work has uncovered the genetic tendency in Alzheimer’s and Parkinson’s, and in diseases of the brain and nervous system.

Seymour Benzer was born in 1921 in New York, the son of Polish immigrants. During his summer holidays in the countryside as a young boy he had his first experiences as a biologist, catching frogs and dissecting them. He was given a microscope for his 13th birthday, a present that “opened up the whole world”, and set him on a firm scientific course.