Questions about Evolution
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Natural Selection

Here are all the basic questions answered.

Q: What is evolution?

A: Biological evolution refers to the cumulative changes that occur in a population over time. These changes are produced at the genetic level as organisms' genes mutate and/or recombine in different ways during reproduction and are passed on to future generations. Sometimes, individuals inherit new characteristics that give them a survival and reproductive advantage in their local environments; these characteristics tend to increase in frequency in the population, while those that are disadvantageous decrease in frequency. This process of differential survival and reproduction is known as natural selection. Non-genetic changes that occur during an organism's life span, such as increases in muscle mass due to exercise and diet, cannot be passed on to the next generation and are not examples of evolution.

Q: Isn't evolution just a theory which hasn't been proven by anyone?

A: In science, a theory is a rigorously tested statement of general principles that explains observable and recorded aspects of the world. A scientific theory therefore describes a higher level of understanding that ties "facts" together. A scientific theory stands until proven wrong -- it is never proven correct. The Darwinian theory of evolution has withstood the test of time and thousands of scientific experiments; nothing has disproved it since Darwin first proposed it more than 150 years ago. Indeed, many scientific advances, in a range of scientific disciplines including physics, geology, chemistry, and molecular biology, have supported, refined, and expanded evolutionary theory far beyond anything Darwin could have imagined.

 

Q: Are all species related?

A: Yes. Just as the tree of life illustrates, all organisms, both living and extinct, are related. Every branch of the tree represents a species, and every fork separating one species from another represents the common ancestor shared by these species. While the tree's countless forks and far-reaching branches clearly show that relatedness among species varies greatly, it is also easy to see that every pair of species share a common ancestor from some point in evolutionary history. For example, scientists estimate that the common ancestor shared by humans and chimpanzees lived some 5 to 8 million years ago. Humans and bacteria obviously share a much more distant common ancestor, but our relationship to these single-celled organisms is no less real. Indeed, DNA analyses show that although humans share far more genetic material with our fellow primates than we do with single-celled organisms, we still have more than 200 genes in common with bacteria.

It is important to realize that describing organisms as relatives does not mean that one of those organisms is an ancestor of the other, or, for that matter, that any living species is the ancestor of any other living species. A person may be related to blood relatives, such as cousins, aunts, and uncles, because she shares with them one or more common ancestors, such as a grandparent, or great-grandparent. But those cousins, aunts, and uncles are not her ancestors. In the same way, humans and other living primates are related, but none of these living relatives is a human ancestor.

Q: What is a species?

A: Members of one species do not normally interbreed with members of other species in nature. Sometimes, members of different species, such as lions and tigers, can interbreed if kept together in captivity. But in nature, geographic isolation and differences in behavior, such as choice of habitat, keep these sorts of closely related animal species apart. Similarly, closely related species of plants can sometimes be hybridized by horticulturists, but these hybrids are rarely found in nature. A species, then, is defined by science as a group of interbreeding or potentially interbreeding populations that is reproductively isolated from other such groups.

Q: What do genes have to do with evolution???

A: Genes are the portions of an organism's DNA that carry the code responsible for building that organism in a very specific way. Genes -- and, thus, the traits they code for -- are passed from parent to offspring. From generation to generation, well-understood molecular mechanisms reshuffle, duplicate, and alter genes in a way that produces genetic variation. This variation is the raw material for evolution.

Q: So what does sex have to do with evolution?

A: Sexual reproduction allows an organism to combine half of its genes with half of another individual's genes, which means new combinations of genes are produced every generation. In addition, when eggs and sperm are produced, genetic material is shuffled and recombined in ways that produce new combinations of genes. Sexual reproduction thus increases genetic variation, which increases the raw material on which  selection operates. Genetic variation within a species -- also known as genetic diversity -- increases a species' opportunity for change over successive generations.

Q: Is evolution just a random process?natural

A: Evolution is not a random process. The genetic variation on which natural selection acts may occur randomly, but natural selection itself is not random at all. The survival and reproductive success of an individual is directly related to the ways its inherited traits function in the context of its local environment. Whether or not an individual survives and reproduces depends on whether it has genes that produce traits that are well adapted to its environment.

Q: Are evolution and 'survival of the fittest' (see Theories page) the same thing?

A: Evolution and "survival of the fittest" are not the same thing. Evolution refers to the cumulative changes in a population or species through time. "Survival of the fittest" is a popular term that refers to the process of natural selection, a mechanism that drives evolutionary change. Natural selection works by giving individuals who are better adapted to a given set of environmental conditions an advantage over those that are not as well adapted. Survival of the fittest usually makes one think of the biggest, strongest, or smartest individuals being the winners, but in a biological sense, evolutionary fitness refers to the ability to survive and reproduce in a particular environment. Popular interpretations of "survival of the fittest" typically ignore the importance of both reproduction and cooperation. To survive but not pass on one's genes to the next generation is to be biologically unfit. And many organisms are the "fittest" because they cooperate with other organisms, rather than competing with them.

Q: How does natural selection work?

A: In the process of natural selection, individuals in a population who are well-adapted to a particular set of environmental conditions have an advantage over those who are not so well adapted. The advantage comes in the form of survival and reproductive success. For example, those individuals who are better able to find and use a food resource will, on average, live longer and produce more offspring than those who are less successful at finding food. Inherited traits that increase individuals' fitness are then passed to their offspring, thus giving the offspring the same advantages.

Q: How do organisms evolve?

A: Individual organisms don't evolve. Populations evolve. Because individuals in a population vary, some in the population are better able to survive and reproduce given a particular set of environmental conditions. These individuals generally survive and produce more offspring, thus passing their advantageous traits on to the next generation. Over time, the population changes.

Q: So this proved God isn't real right?

A: Wrong, Many people, from evolutionary biologists to important religious figures like Pope John Paul II, contend that the time-tested theory of evolution does not refute the presence of God. They acknowledge that evolution is the description of a process that governs the development of life on Earth. Like other scientific theories, including Copernican theory, atomic theory, and the germ theory of disease, evolution deals only with objects, events, and processes in the material world. Science has nothing to say one way or the other about the existence of God or about people's spiritual beliefs.

Q: How long does evolution take?

A: Even though evolution is taking place all around us, for many species the process operates so slowly that it is not observable except over thousands or hundreds of thousands of years -- much too long to witness in a human lifetime. There are cases in quickly reproducing life forms like bacteria and fruit flies, however, where evolution can be seen happening in a matter of weeks for the bacteria and many months for the flies. In these cases the relatively large number of generations in a given period of time is key, since evolutionary change occurs incrementally from one generation to the next. All else being equal, the more generations you have, the more quickly evolution happens.

Q: How can evolution produce such amazing organs, like the eye, or reproductive system.

A: In the process of natural selection, individuals in a population who are well-adapted to a particular set of environmental conditions have an advantage over those who are not so well adapted. These individuals pass their genes and advantageous traits to their offspring, giving the offspring the same advantages. Generation after generation, natural selection acts upon each structure within an organ like the eye, producing incremental improvements in the process. Each tiny change in a structure is dependent upon changes in all the other structures. In this way, individual parts of a system evolve in unison to be both structurally and functionally compatible. Eventually, over thousands and sometimes millions of years, the small improvements add up -- the simple, systematic process has produced an almost unfathomably complex organ. Recently, scientists have found clues to the evolutionary pasts of some of the most complex organs, helping to clarify how this process works.

Q: Can one species become another?

A: One species does not "turn into" another or several other species -- not in an instant, anyway. The evolutionary process of speciation is how one population of a species changes over time to the point where that population is distinct and can no longer interbreed with the "parent" population. In order for one population to diverge enough from another to become a new species, there needs to be something to keep the populations from mixing. Often a physical boundary divides the species into two (or more) populations and keeps them from interbreeding. If separated for long enough and presented with sufficiently varied environmental conditions, each population takes its own distinct evolutionary path. Sometimes the division between the populations is never breached, and reproductive isolation remains intact purely for geographical reasons. It is possible, though, if the populations have been separate for long enough, that even if brought back together and given the opportunity to interbreed they won't, or they won't be successful if they try.

Q: If humans evolved form apes, why are there still apes these days?

A: Humans did not evolve from present-day apes. Rather, humans and apes share a common ancestor that gave rise to both. This common ancestor, although not identical to modern apes, was almost certainly more apelike than humanlike in appearance and behavior. At some point -- scientists estimate that between 5 and 8 million years ago -- this species diverged into two distinct lineages, one of which were the hominids, or humanlike species, and the other ultimately evolved into the African great ape species living today.

Q: Are we influencing evolution?

A: Most scientists would agree unequivocally that humans have greatly affected the process of evolution, from the rise of antibiotic and pesticide resistance to the largely human-caused increase in the extinction rate. Our effect on the process of evolution even extends to our own species' evolution. Technology and culture have protected us to a great extent from the selective pressures that drive evolution, allowing many people -- especially those in developed nations who, without medical intervention, would not live to reproductive age -- to pass their genes on to the next generation. Other scientists note that technology and culture have changed but not eliminated the role of natural selection on our species. We now adapt to crowding, pollution, and new disease rather than the necessity to escape from large predators. Humans will change in the future, but are unlikely to evolve into a new, separate species because no human group is truly isolated anymore, given our transportation systems. Without genetic isolation, there is no further opportunity for speciation among humans.

Q: Could apes ever evolve into some other humanlike creature?

A: It is possible that in many millions of years present day apes could evolve into some other humanlike species. It is, however, very improbable. First of all, humans did not evolve from any of the species we know as apes today. At some point 5 to 8 million years ago, the common ancestor of humans and modern apes diverged to form the two separate lineages we know today. The species at the end of these lineages are a result of a very specific combination of selection pressures and genetic mutations over millions of years. This same combination is highly unlikely to occur ever again.

Q: Why do some species survive while others become extinct?

A: Extinction is often caused by a change in environmental conditions. When conditions change, some species possess adaptations that allow them to survive and reproduce, while others do not. If the environment changes slowly enough, species will sometimes evolve the necessary adaptations, over many generations. If conditions change more quickly than a species can evolve, however, and if members of that species lack the traits they need to survive in the new environment, the likely result will be extinction.