Henderson - 50 Genetics Ideas You Really Need to Know

CLASSICAL GENETICS

MOLECULAR BIOLOGY

THE GENOME

NATURE AND NURTURE

GENES AND DISEASE

SEX, HISTORY AND BEHAVIOR

GENETIC TECHNOLOGIES

THE NEW GENETICS

you really need to know

Mark Henderson

New York London

2009 by Mark Henderson

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We are living through a revolution in human understanding. For as long as our species has been capable of complex thought, people have wondered where we come from, why we behave as we do, how our bodies work in sickness and in health, and why we all seem so similar and yet display such diverse and wonderful individuality. Philosophy and psychology, biology, medicine and anthropology, even religion, have all attempted to supply answers, and not without some success. But until very recently, we have been missing a fundamental piece of the puzzle, with significance for every aspect of human existence. A knowledge of our genetic code.

Genetics is a young science. It is little more than 50 years since Crick and Watson discovered the structure of the DNA molecule in which organisms cellular instructions are written. The first, incomplete, draft of the human genome was published only in 2001. Yet this infant branch of knowledge is already changing the way we understand life on Earth, and genetic technology is transforming the way we live.

Genetics has shed fresh light on our history, proving the fact of evolution, and allowing us to trace how the first humans emerged from Africa to populate the world. It has brought us new forensic tools that can convict the guilty and exonerate the innocent. And it is explaining how our individuality is forged through nature and nurture. We are also entering a new era of genetic medicine, which promises treatments tailored to patients genetic profiles, spare part tissue grown from stem cells, gene therapy to correct harmful mutations, and tests that highlight inherited health risks that might then be reduced.

These incredible opportunities also stir ethical concerns. Issues such as genetic engineering, cloning, genetic discrimination and designer babies often suggest that DNA stands not for deoxyribonucleic acid, but for controversy.

We are, of course, much more than the sum of our genes. We are rapidly learning that other parts of the genome, such as the segments once derided as junk DNA, are also important, perhaps more so. And as we grasp more about genetics, we are enhancing our understanding of other factors that count tooour lifestyles, our environments, our interactions with other people.

Without genetics, however, we would look at life with one eye. We are lucky enough to live at a time when humanity can finally watch with two.

Charles Darwin: There is grandeur in this view of life that from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Nothing in biology, wrote the geneticist Theodosius Dobzhansky, makes sense except in the light of evolution. It is a truth that applies particularly strongly to its authors specialist field. Though Charles Darwin had no concept of genes or chromosomes, those concepts and all the others that will be described in this book have their ultimate origins in the genius of his insights into life on Earth.

Darwins theory of natural selection holds that while individual organisms inherit characteristics from their parents, they do so with small and unpredictable alterations. Those changes that promote survival and breeding will multiply through a population over time, whereas those that have negative effects will gradually disappear.

As is often the case with truly great ideas, evolution by natural selection has a beautiful simplicity that, once grasped, immediately becomes compelling. When the biologist Thomas Henry Huxley first heard the hypothesis presented, he remarked: How extremely stupid not to have thought of that! Once a skeptic, he became evolutions most vociferous champion, earning the nickname Darwins bulldog.

The argument from design For centuries before Darwin, natural philosophers had sought to explain the extraordinary variety of life on Earth. The traditional solution, of course, was supernatural: life, in all its diversity, was created by a god, and the traits that fit a particular organism to an ecological niche were a function of the creators grand plan.

This argument from design dates back at least to the Roman orator Cicero, but it is most commonly associated with William Paley, an English clergyman. In an 1802 treatise, he likened the intricacy of life to a watch found on a heath, the very existence of which presupposes the existence of a watchmaker. It rapidly became scientific orthodoxyeven Darwin was much taken with it early in his career.

As was already clear to the philosopher David Hume in the 18th century, however, the argument from design begs the question: who designed the designer? The absence of an obvious naturalistic explanation for a phenomenon is a poor reason to look no further. Those who make it, from Paley to todays rebranded intelligent design creationists, are essentially saying: I dont understand, so God must have done it. As a way of thinking, it is no substitute for science.