What are the discoveries made that supports the theory of evolution?
The theory of evolution has always been debated over, and other arguments like intelligent design and creationism come in as reasons for the origin of life. However, there are many discoveries made which support the theory of evolution, and many discoveries are constantly being made. Research and experimentation are also being constantly carried out to ensure the validity of these theories.
Discoveries that support the theory of evolution are classified into 6 categories: Paleontology, Comparative Anatomy and Molecular Biology, Biogeography, Recorded Genetic Changes, Vestigial Structures and Embryology
Paleontology:
- Fossil record of change in the earlier species of living organisms
- Remains of living organisms in sedimentary rock gives us an idea of how living organisms looked like in the past
- It is a record of past changes through time and is more or less accurate
- Shows us that a wide variety of living organisms were present from the past till now
- Many of these fossils show similar traits to living organisms now, showing us that species are not rigid and can change into another species over time
- Transitional fossils: fossils showing the middle stage between organisms now and millions of years ago.
- The type of sedimentary rock from which the fossil was found in gives a clue as to how long ago the living organism died
- However there are limitations to how much fossils can tell us about the past. More often than not, bones of living organisms in the past get crushed or consumed before they can be fossilized
- Environments at which the past organisms died also play a part
- Natural disasters can also destroy the fossils before they are fully formed, and all these factors contribute to the large gaps in the fossil records.
Comparative Anatomy and Molecular Biology:
- All living organisms are fundamentally similar: we all start off from cells, we are all made up of cells, and we all live, grow old and eventually die.
- The DNA code is similar for all living things, indicating a molecular unity of life.
- One main anatomical similarity that supports the theory of evolution is that of the bones of vertebrates. All vertebrates have a similar structure of bones, namely the humerus, radius and ulna. These vertebrates retain these traits from their common ancient vertebrate ancestor.
- The concept of common ancestry is obvious; related organisms share many similar characteristics and as the relatedness of these organisms increase, so do the number of comparable characteristics.
- This is also rather obvious in the world we live in now
- However, it is hard for us to determine evolutionary relationships based on comparing anatomies when we look at similar structures in animals, like wings for example. Insects and birds might look as if they have common winged-ancestors but we cannot safely say that just because they both have wings.
- Another limitation we might have when comparing anatomies of living organisms has to do with embryology. Some organisms which do not look the same in the adult form might have looked extremely similar when they were embryos.
- For example, humans and fish share homologous traits because both their embryo stages see their embryos having gill-like features, even if this is not present in the adult stages.
Biogeography:
- Another evidence that evolution has taken place (and is still taking place) is that of geographical distribution of related species of animals. The Earth started off with only one large area of land, and so all animals had the same environment to live in. But as millions of years went by, the large area of land got separated into many different countries and continents and animals of the same species were forced to live away from one another. These animals be then start to look different because of many different factors. However, we understand that they have come from the same ancestors but because of evolution, they have changed slightly.
- Isolated islands like Australia have had animals evolve on their own, which is clearly shown by the unique biotic environments, with unique species of animals which are unable to be found in other parts of the world.
- Biogeography is a part of natural selection, and it causes speciation to occur. Speciation is when the same organisms develop/change based on the requirements of their environment. As years go by, these organisms will eventually make up different species.
Recorded Genetic Changes:
- Natural populations all have genetic diversities; when faced with great environmental changes, many populations will be wiped out, but a few individuals in these populations will survive these changes.
- These individuals will eventually reproduce, and the new generation will be immune to further environmental changes. This is also a part of natural selection, or the survival of the fittest.
- When natural selection occurs, evolution occurs as well.
Vestigial Structures:
- Many organisms have some features which do not seem to be of much use to them. For example, the tailbone of humans and the human appendix. These are called vestigial structures.
- This is evidence that evolution has taken place as these features might have been of great use to the organisms in the past and as environments change, these features serve no purpose eventually as organisms no longer need them for survival.
- However, these features are still retained as they serve anatomical roles.
- Vestigial structures are observed as some parts of past organisms serve no purpose in the near future, but are harmless to the organisms, and hence take a longer time to be phased out from the organisms themselves.
Embryology:
- At many points in time, we claim that organisms which do not look like one another are entirely different and do not belong to a common ancestor. However, embryology then proves us wrong.
- Embryos of different organisms might actually look the same, for example that of the rabbit and the human. We can then infer that these organisms might have shared a common ancestor but because of evolution and environmental changes, these organisms change drastically and become different.
- Embryology suggests that many organisms came from the same ancestor.
Why do scientists readily accept this theory?
In science, a theory is defined as “a set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena”. (http://dictionary.reference.com/browse/theory) Theories are testable and are not fixed. When proved wrong and inaccurate, they can be changed and even dismissed. Evolution is classified as a theory along with others like gravity or the atomic theory, which are all universally accepted by all scientists.
Evolution has been thoroughly tested, and has scientific physical evidences in areas such as biochemistry, paleontology and so on. Evolution also lays the foundation for what we know about genetics as well as adaptation of living organisms to their surroundings, and many more scientific areas.
Another reason why scientists readily accept this theory is because other arguments are invalid and not supported by physical evidences and logical explanations. Intelligent Design and Creationism do not meet the requirements of a scientific theory; they’re not based on direct observations or experiments. Intelligent design is “the argument for the existence of God”, while Creationism is “the belief that humanity, life, the Earth and the universe were created in their entirety by a supernatural deity (usually God)”. (http://en.wikipedia.org) Hence these arguments and reasonings are not accepted by scientists.
How valid are these evidences that support this theory?
Paleontology:
- Largely valid, because there is physical evidence in the form of fossils to support how organisms from the past look like living organisms now, or have some common features. (e.g.: Diacodexis (Dinosaur) à Whale)
- However it is also invalid to some extent as the fossils may have been damaged and interpreted wrongly but archaeologists would not know it.
Comparative Anatomy and Molecular Biology:
- This evidence is rather valid because there is an obvious phenomenon that some animals have similar features and most likely share a common ancestor. Some examples include the dog and the wolf, which have a lot of similar traits. And DNA comparisons also show that many related animals have similar genes, like humans and chimpanzees, having 98.7% of genes similar to one another.
- Bone structures also give an idea that evolution has definitely taken place through the many millions of years as most vertebrates have the same type of bones that make up their limbs even though on the outside these organisms may look entirely different.
- However, this may also be argued as invalid as the similarities both anatomy and molecular structure may be coincidental, but this is not well supported by evidences.
Biogeography:
- Biogeography is largely valid as it proves evolution through speciation over the years. One example would be Darwin’s Finches. –include diagram- Darwin’s Finches show that the Finches generally have the same appearance with the exception of their beaks, which vary according to the environment they lived in.
- However, this evidence might not be very substantial as we have yet to find out the true origin of life. Although it has been proven that land on earth started off as one area of land, we cannot safely say that all animals came from only one ancestor of their kind. There might have been 2 or more different species then, resulting in the biodiversity.
Recorded Genetic Changes:
- These recorded changes are definitely valid as we see very clear changes in living organisms when changes to their environments occur.
- One pertinent example will be the evolution of bacteria through natural selection. Bacteria get immune to antibiotics very rapidly; medical doctors hesitate when giving antibiotics to their patients as the bacteria in the patient’s body may get immune to the antibiotic really soon.
- Insects also evolve really quickly, and this is seen when humans have to constantly come up with new formulae for pesticides to kill insects because they get immune to pesticides very easily.
- Hence from all this, we can safely say that recorded genetic changes is a valid evidence to say that evolution has occurred and is definitely still occurring.
Vestigial Organs:
- The existence of vestigial organs might be a lead that evolution has occurred, but it is a very weak evidence as we cannot safely conclude that these vestigial structures were of use to the past organisms. They might have been used as anatomical structures right from the origin of the organism.
- On the other hand, animals like whales and snakes have vestigial pelvic and leg bones, and from studies, it has been proven that their ancestors could walk on land. Therefore this is a clear example of evolution, although it is not a definite way of proving evolution.
Embryology:
- Embryology safely indicates that organisms in a large group of their kind (e.g.: mammals) share a common ancestor in one way or another because their embryos are extremely similar. From this, we can then conclude that evolution definitely occurs because mammals look extremely different in their adult form because of the different environments they live in.
- Some examples extend beyond animals in a same group. A good example would be the human embryo and the embryo of fishes. Embryos of humans pass through a stage whereby gills are present on them, gills much similar to those on embryos of fishes.
- Therefore, embryology is a good way of proving evolution has occurred when organisms in the adult forms do not show striking resemblances in any way. However, it does not prove to us how it causes the biodiversity of the organisms in today’s world.
Sources:
Lines of evidence
http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_01
Early Theories of Evolution
http://anthro.palomar.edu/evolve/evolve_3.htm
Sparknotes summary
http://www.sparknotes.com/biology/evolution/evidence/summary.html
Picture of Forearmbs
http://faculty.evansville.edu/de3/evolutionweb2/forearms.jpg
Picture of Chimpanzee and Human
http://img.timeinc.net/time/daily/2006/0609/monkey_0930.jpg
Picture of Embryology
http://nitro.biosci.arizona.edu/courses/EEB182/Lecture02/figures/embryo.gif
Beyond Natural Selection
- By Robert Wesson