Darren Naish - Evolution in Minutes

EVOLUTION IN MINUTES

DARREN NAISH

EVOLUTION IN MINUTES

DARREN NAISH

CONTENTS

Introduction

Evolution by natural selection is the foundational concept in our study of the natural world. One of the most significant scientific discoveries ever made, it has revolutionized every aspect of our understanding both of the past, and of the diversity of living things today. It even allows us to make predictions about organisms that will evolve in the future. Indeed, evolution has phenomenal explanatory power: to quote biologist Theodosius Dobzhansky, nothing makes sense in biology except in the light of evolution.

Evidence for evolution is everywhere, and studies show how the processes and events that together drive evolutionary change are continually present in every single community of living things. The result is that at least some knowledge of evolution is essential for anyone interested in the natural world. Nevertheless, the actual mechanism is complex and involves numerous different concepts, processes and events. New discoveries are constantly made. In fact, evolutionary

6 INTRODUCTION

science is often at the forefront of the news as advances in genetics, new fossil discoveries, and new data pertaining to the link between genetics and development are announced.

Some people, however, contend that the fact of perpetual change in nature challenges the words of certain sacred texts. For this reason, evolution is often controversial and even politicized. Religious leaders, politicians, celebrities and artists routinely comment on the topic, and it has been at centre stage in court cases and in arguments about education and public policy. The battle to teach children about evolution remains a pertinent one in some parts of the world.

In this book, we look at the key evidence for evolution, and the developing ideas of the 19th and 20th centuries. We investigate the principles, concepts and trends within evolution, and see how it has affected the history of life on geological timescales, and shaped the development of our own species. We end by considering the future of evolution: human-caused change, genetic modification and the possible role of cybernetics.

The idea that living things change over time is basic, elegant in its simplicity, crucial, and fascinating, but there is still much to learn.

What is evolution?

The term evolution relates to heritable change that occurs in living organisms over generations. That is, to change that occurs as one generation gives rise to the next. Because evolution take place on this gradual, generational scale, changes are often tiny and extremely slow to accrue or become obvious. However, this is not always the case. In organisms that grow and reproduce quickly, evolution can be rapid enough that changes are observed over the course of decades, or even years.

Evolution should not be confused with metamorphosis the process by which living things change during the course of their lifetime. Nor, when we discuss biological evolution, are we discussing such things as the origin of life itself, or cosmological events, such as the creation of Earth or the Big Bang. The process of evolution is typically associated with the changes that affect natural populations of living things. However, organisms modified by people also evolve. In such cases, it can be said that humans control or shape their evolution (see page 26).

8 WHAT IS EVOLUTION?

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Different bill shapes among Galapagos finches offered the young Charles Darwin a vital clue to the evolutionary mechanism.

The evidence for change

The idea that organisms change over the generations is supported by four facts. The first is that some organisms are similar to others, yet different enough that they have alternative lifestyles and do not interbreed. Zebras are similar to horses, for example. The second fact is that humans have modified many organisms flowering plants, dogs and so on by selecting individuals to breed with one another in order to emphasize specific features. If humans can cause such changes to occur over the generations, natural processes can too.

The third fact is that fossils show how living things have become smaller or larger over time, and how their parts changed shape or took on new functions. The fourth fact is that change over the generations has been observed in laboratory and natural settings. Scientists have observed generational changes in microscopic organisms and also in insects, fish, mice, lizards and birds. In some cases, the changes have been significant enough that we can probably talk about witnessing the origin of a new species.

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The origin of species

If evolution refers to heritable changes that occur across generations, then it mostly concerns changes that happen on a small scale in, say, members of a single population of a single species. This is the kind of evolution that scientists have most frequently observed. However, if such changes are happening, it follows that, should they continue for a sufficient period of time, a population will eventually become distinct enough from related populations that a new species will have emerged, or originated.

This issue formed the focus of Charles Darwins pioneering book of 1859, titled The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Darwins model for the origination of species does not pertain to the origin of life as a whole, nor did Darwin understand how the information inherited by organisms was passed down across the generations. Substantial additional research was inspired by his proposal and continues today. Darwins research and reasoning are also themselves a major area of modern investigation.

12 WHAT IS EVOLUTION?