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- Isn't Evolution "only a theory"?
- What is the meaning of the phrases "natural selection"
and "survival of the fittest"?
- How can Evolution be scientific if it can't be
tested and none of the events described can be observed or re-created?
- Isn't there an increasing number of scientists
who doubt each other's explanations of the evolutionary theory?
- If humans descended from monkeys, why are there
- How can Evolution explain how life first appeared
on Earth if nobody was there?
- Evolution can not explain how something as complex
as a protein, let alone a living cell or a human, could spring
up by chance.
- How is it possible that multicellular life evolved
from protozoa if the Second Law of Thermodynamics says that systems
must become more disordered over time?
- If mutations can only eliminate traits how can
they produce new features?
- How can natural selection explain the origin of
new species and higher orders of life?
- Are there any transitional fossils?
- Living things have fantastically intricate features,
shouldn't they be the products of intelligent design, not evolution?
Many people hold the common belief that a theory is more certain than a hypothesis but less certain than a law. Scientists do not use these terms that way and when scientists talk about the theory of evolution they are not expressing reservations about its truth.
For scientists a theory is a rigorously tested statement of general principles that explains observable and recorded aspects of the natural world. A theory is not just an "idea". Typically considerable evidence is gathered first and the theory will develop from that. A theory can incorporate facts, laws, inferences, and tested hypotheses and is a well-substantiated explanation of some aspect of the natural world. No amount of validation changes a theory into a law.
A scientific theory stands until proven wrong -- it is never proven correct. Darwin's 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. 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.
Fossil record and abundant evidence from species comparisons testifies that organisms have evolved through time and provide the facts of evolution. These facts can be tied together and provide evidence and support for the theory of evolution. The absence of direct observation does not make conclusions from the evidence less certain.
"Survival of the fittest" is a popular term to describe the process of natural selection, a key mechanism that drives evolutionary change. A more technical description speaks of differential rates of survival and reproduction. Rather than labelling species as more or less fit, 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. These better adapted individuals are more likely to successfully reproduce and leave offspring, so that over time their genes spread through the population.
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 only to the ability to survive and reproduce in a particular environment. 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. Diversification of a species from single ancestors may be due to geographical or behavioural reasons and can help a species to adapt in changing environments.
Here is an excellent example of how sympatric speciation can occur
in animals (parasitic indigobirds).
Observation and the collection of evidence are the building blocks of all scientific inquiry; evolutionary science is no different. The field of evolution is divided into at least two broad areas: microevolution and macroevolution. Microevolution looks at changes within species over time using laboratory tests and observation. Macroevolution studies how taxonomic groups above the level of species change from examining collected evidence provided by fossil record and DNA comparisons that help to reconstruct how various organisms may be related.
Microevolution uses tests in the laboratory such as studies of cells, plants and fruit flies and direct observation in the field. These days even most creationists acknowledge that microevolution has been upheld by tests and observation. A good example of a microevolution observational study is Peter & Rosemary Grant's studies of evolving beak shape among Galápagos finches. There is also a good example for microevolution in evolving tusklessness in elephants where poaching pressure is high in Dobson's study. Both of these studies are well covered in Jonathan Weiner's excellent 1995 book titled, "The beak of the finch", (New York:Vintage Press)
Work on macroevolution involves the study of fossils, embryology, comparative anatomy and DNA rather than direct observation. Historical sciences like astronomy, geology and archaeology, as well as evolutionary biology, can test hypotheses by checking whether they accord with physical evidence and whether they lead to verifiable predictions about future discoveries.
All scientists like to debate over various topics and constantly question each other's explanations, and in fact that is the nature of science, but acceptance of evolution as a factual occurrence and a guiding principle is nonetheless universal in biology. Pick up any issue of a peer-reviewed biological journal, and you will find articles that support and extend evolutionary studies or that embrace evolution as a fundamental concept.
Sometimes comments of scientists are taken out of context to better serve the interests of those making the report, even to exaggerate or distort. When confronted by statements of scientific authorities that are supposed to question evolution always ask for the original article or book they came from. The original version from the scientist-author will almost certainly present evolution in a supportive light.
Evolution does not teach that humans evolved from present-day monkeys rather that humans and monkeys share a common ancestor that gave rise to both.
New species evolve by splintering off from established ones, when populations
of organisms become isolated from the main branch of their family and acquire
sufficient differences to remain forever distinct. The parent species may
survive indefinitely thereafter, or it may become extinct. 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. In the case of humans and monkeys both groups have continued to survive from an original source species which has not.
The evolution of early life is one of the most compelling mysteries of modern biology but one that is slowly yielding to patient research. Certain pieces of that puzzle are clearly missing, but others seem very much in place. One of the most firmly established pieces is how the first protective coats formed in the rich organic "soup" from which life evolved. Just as with energy flow, the key to both early and present-day membranes lies in the nature of electrons and their polarity. Just as electrons and nuclei attract one another because of their opposite charges, the oppositely charged ends of polar molecules bind weakly to one another.
Countless microevolutionary and macroevolutionary tests confirm these
explanations however, one of the best current explanations to picture early liposomes forming around concentrations of energy-rich nutrients.
These nutrients formed as the result of the energy of lightning and ionizing radiation
acting on simple chemicals found in the earths' early atmosphere. Astrochemical analyses hint that quantities of these compounds might have originated in space and fallen to earth in comets, a scenario that may solve the problem of how those constituents arose under the conditions that prevailed when our planet was young.
Find more information about the early beginnings of life on this
Most of Earth's history has to be explained in the absence of humankind,
traced back by posing questions and finding the answers that fit
best (and of course can be tested) and make sense. We were not
there when dinosaurs were around or Moas for example (only our
ancestors), but by experimenting with different scenarios we can
aim to get closer to an answer.
Evolution does not depend on chance to create organisms however chance does play a part in evolution for example, in the random mutations that can give rise to new traits. The principal known mechanism of evolution is natural selection which harnesses non-random change by preserving "desirable" features and eliminating "undesirable" ones. As long as the forces of selection stay constant, natural selection can push evolution in one direction and produce sophisticated structures in surprisingly short times.
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. 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.
In the case of the relatedness of humans and single-celled organisms, a journey along two different paths, one starting at the tip of the human branch, the other starting at the tip of a single-celled organism's branch, would ultimately lead to a fork near the base of the tree: the common ancestor shared by these two very different types of organisms. This journey would cross countless other forks and branches along the way and span perhaps more than a billion years of evolution, but it demonstrates that even the most disparate creatures are related to one another, that all life is interconnected.
The Second Law of Thermodynamics states that all chemical and physical processes in a closed system (one that no energy or matter leaves or enters) tend to drive that system toward maximum entropy. Entropy is a physical concept often described as the amount of disorder in a system. The word disorder as a physical term differs significantly from the conversational use of the word. The Second Law states that in a closed system no energy gain or loss can happen, unless other compensating activities are taking place. Earth is not a closed system, because there is a continual input of energy from the sun thus the Second Law of Thermodynamics does not apply to
Simple organisms can fuel their rise toward complexity by consuming other forms of life and nonliving materials.
Mutations do not necessarily "eliminate" traits although they may generate new ones. A mutation can be defined as a change in genetic material that results from an error in replication of DNA. Mutations can be beneficial, harmful, or neutral.
Point mutations (changes at precise positions in an organism's DNA i.e. changes involving a single base in the DNA) have produced many new traits such as bacterial resistance to antibiotics. Apparently harmful mutations may be beneficial in some contexts. A good example is sickle-cell anaemia, a recessive condition caused by a single mutation. While individuals who have 2 copies of the harmful allele face a whole range of health problems (not only severe anaemia), individuals who are heterozygous (possess one normal and one harmful allele) are protected against malaria. This maintains the recessive allele in the population. Similarly, people who are heterozygous for thalassaemia (another form of anaemia) are also protected against malaria. Consequently, both the sickle-cell allele and the thalassaemia allele are more common in regions where malaria is endemic (sickle-cell in Africa, thalassaemia in the Mediterannean).
Molecular biology has discovered mechanisms for genetic change that go beyond point mutations, and these expand the ways in which new traits can appear. Functional modules within genes can be spliced together in novel ways. Whole genes can be accidentally duplicated in an organism's DNA, and the duplicates are free to mutate into genes for new, complex features, which natural selection can then test for possible uses.
Individual new 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 general population changes.
If a population of organisms were isolated from the rest of its species by geographical boundaries,
or behavioural traits, it might be subjected to different selective pressures. Changes would accumulate in the isolated population. If those changes became so significant that the splinter group could not or routinely would not breed with the original stock, then the splinter group would be reproductively isolated and on its way toward becoming a new species (allopatric speciation).
A fossil or group of fossils that represents a series of similar species, genera, or families, that link an older group of organisms to a younger group is called a transitional fossil. Often, transitional fossils combine some traits of older, ancestral species with traits of more recent species (for instance, a series of transitional fossils documents the evolution of fully aquatic whales from their terrestrial ancestors).
Palaeontologists know of many detailed examples of fossils intermediate in form between various taxonomic groups. One of the most famous fossils of all time is
Archaeopteryx, which combines structures peculiar to birds with features of dinosaurs. A sequence of fossils spans the evolution of modern horses from the tiny
Eohippus. Perhaps 20 or more hominids (not all of them our ancestors) fill the gap between Lucy the australopithecine and modern humans.
for well presented information about Archaeopteryx including explanations
of his bird and dinosaur like features. http://www.pbs.org/lifeofbirds/evolution/
is a website also presents good information on how birds developed
"Intelligent design theory" is built on the belief that evolution does not sufficiently explain the complexity that exists in life on Earth and that science should recognize the existence of an "intelligent designer." Proponents criticize evolution by trying to demonstrate that it could not account for life as we know it and then insist that the only tenable alternative is that life was designed by an unidentified intelligence. They assert that their criticism of evolution is scientific, not religious. But the various aspects of intelligent design theory have not yet been subjected to the normal process of scientific experimentation and debate, nor have they been accepted by the scientific community.
Critics have tried to counter Darwin's theory of evolution by citing
the example of the eye as a structure with intricate features that
could not have evolved. They say that the eye's ability to provide
vision depends on the perfect arrangement of its parts and natural
selection could never favour the transitional forms needed during
the eye's evolution--what good is half an eye? However, Biology
researchers have identified primitive eyes and light-sensing organs
throughout the animal kingdom and have even tracked the evolutionary
history of eyes through comparative genetics. Another example of how
complex structures can be broken into less complex but still
functional subunits is the bacterial flagellum.
Proponents of "creation science" hold that intelligent design or special creation- the conviction that God created the universe, including humans and other living things, at one time in the relatively recent past - can be supported using the methods and theory of science. Scientists from many fields have examined these ideas and have found them to be scientifically insupportable. For example, evidence for a very young Earth is incompatible with many different methods of establishing the age of fossils and geological formations. Furthermore, because the basic proposals of creation science are not subject to test and falsification like scientific theories, these ideas do not meet the criteria for science.
No research supporting the claims of intelligent design has ever been published in any recognized, professional, peer-reviewed scientific journal. Finally, the question of whether there is an intelligent designer is un-testable using the methods of science, and therefore is not a scientific claim.