Transcription
The story of inheritance begins like many things, with the ancient Greeks. Aristotle, fresh from inventing logic itself, noted that children often look like their parents. But exactly why was far from clear. Sometimes they look like mum, sometimes dad, and sometimes their grandparents.
Aristotle decided that the man determined the form of the child, whilst the woman provided the material. He planted the seed, she provided the soil that fed it. And for hundreds of years, this was as far as people got.
The first clues to what actually goes on inside women came in the 1600s. Two Dutch medics announced that women actually produced eggs, like birds. Then they fought over who'd had the idea first, only to discover that a Dane called Neil Stenson had already had the same idea, re-christening the organs formerly known as female testicles as ovaries.
A few years later, another Dutchman, this time a fabric merchant, made a startling discovery by examining the contents of his trousers with a primitive microscope. Semen seemed to be full of tiny creatures that thrashed around like a snake. He discovered sperm.
While finding sperm and eggs were huge leaps forward, confusion still largely reigned. Most people thought babies must start off as perfect miniatures inside either egg or sperm, but no one knew which. For around 150 years, battle raged between the "ovis" and the "sperms." Few thought they could be equally important; they were just too different. And while the debate continued, no one was any wiser as to how children came to look like their parents or grandparents.
By the 1800s, the inheritance question took another giant leap forward, thanks to some funds. Men like Robert Bakewell were a new breed who saw sheep as machines for turning grass into money. So he bred his best males with his best females. The resulting super sheep suggested offspring were a mixture, but naturally, it wasn't quite that simple.
In Austria, a monk called Gregor Mendel had spent years carefully breeding pea plants: tall with short, yellow with green. His results suggested that instead of a simple blend, each offspring received one element for height or color from each of its parents, but that one could override the other. Imagine a black mouse meets a white mouse. If the black dominates the white, the offspring will be black, but the white doesn't disappear. If the mice children get together, they'll sometimes have white babies.
Meanwhile, other scientists looking for answers resorted to rather desperate measures. One biologist chopped the tails of mice to see if their offspring would also be tail-less. They weren't. Darwin's cousin, Francis Galton, tested whether the thing that caused inheritance lived in the blood by giving blood transfusions to rabbits that turned out to be completely different.
Then, in 1909, came the suggestion that what passed from parent to child could be called a gene. And just a year later, whilst breeding flies, Thomas Morgan showed these genes actually lived on tiny structures inside the cell: the chromosomes. The science of genetics had been born.
Scientists delved deeper until Watson and Crick finally revealed the double helix of DNA. So how does inheritance work? Put simply, we receive half our dad's chromosomes from the sperm and half of our mum's from the egg. On these chromosomes are genes, pieces of DNA containing the instructions to make our bodies. They're the basic units of inheritance and affect whether we, and our children's children, end up tall, short, blue-eyed, or curly-haired.