What is evolution?
“Evolution is change in the genetic material of a population of organisms from one generation to the next. “ – Wikipedia. The changes are small between generations however the amount of changes builds up over the course of several generations and can lead to substantial changes or the creation of a new species. Similarities between organisms (more on this later) have led the scientific community that all known species are descended from a common ancestor.
NOTE: EVOLUTION IS USED TO EXPLAIN THE DIVERSITY OF LIFE RATHER THAN THE ORIGINS OF LIFE (ABIOGENESIS )NOTE 2: THE THEORY OF EVOLUTION IS A COMPLETELY SEPARATE THEORY TO THE BIG BANG THEORY (added by Petey)
Terms and definitions-• Common Ancestor-“A group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on earth are descended from a common ancestor or ancestral gene pool.” – Wikipedia.
• Species- A group of organisms which may reproduce and produce fertile viable offspring.
• Organism- Anything which is alive.
• Genome- The total genetic information within an organism.
• Natural selection -the process where heritable traits that make it more likely for an organism to survive long enough to reproduce become more common over successive generations of a population.- Wikipedia
• Phenotype- Any observable trait in an organism E.g. Male/female
• Genotype- An organism’s genetic information for a trait. E.g. XY/XX
• Mutations- Changes in the sequence of genetic material.
• Recessive gene- a gene which is masked by a dominant gene, it is not weaker or worse
• Dominant gene- a gene which masks a recessive gene, it is not stronger or better
How evolution worksHow natural selection worksThere is a misconception that evolution is random process, although mutation is random it is guided through the process of natural selection. Within a species there is a certain extent of variation, these variations affect the chances of an organism from surviving long enough to reproduce. Say for example you have a group of locusts some of the locusts have a resistance to pesticides. Under normal conditions this locusts with resistance have no survival advantage however once the insects are exposed to the pesticides the resistant locusts have a selective advantage over the normal locusts and a greater proportion of the resistant locusts are able to reproduce than the locusts without the resistance. Eventually the resistant locusts make up the entirety of the population.
Nature of DNA+RNABefore I go into mutations and how they affect the organism you need a basic understanding of DNA:
• DNA is made up of 4 nucleotides Thymine (T), Adenine (A), Guanine (G), Cytosine (C)
• DNA is coded in a series of triplets such as AAA TAG ACA
• Each of these triplets codes for one amino acid (see graph below)
• The nucleotide sequences for stop mean start a new protein.
MutationsThere are several types of mutations:
• Deletion- The removal of one or more nucleotides
• Insertion- The addition of one or more nucleotides
• Substitutions- The replacement of a nucleotide for another
• Translocation- swapping of the position of nucleotides
• Frame shift Mutations- An insertion or deletion of nucleotides that is not divisible by three which disrupts the triplet sequence. This can cause major changes in the entire sequence. E.G :
AGT TGA GAT GTC CCG GCA ACG CTG ATC
Ser Stop Asp Val Pro Ala Thr Leu Ile
Now remove the first Adenine
GTT GAG ATG TCC CGG CAA CGC TGA TC
Val Glu Met Ser Gly Gin Arg STOP X
There are also large scale chromosomal mutations:
• Duplications- additional copy/copies of a chromosomal regions leading to an increased dosage of the genes.
• Deletions of large chromosomal regions can lead to the removal of genes
• Translocations- swapping parts of a chromosomes with other chromosomes
• Inversions- reversing the way the chromosome is orientated.
The effect of mutations:
• Silent mutations- mutations which have no effect because the mutation changes the code to an alternative code for the same amino acid.
• Lethal mutations- Mutations which kill the organism
• Loss of function Mutations- Mutations which impair the function or stop the gene working entirely. This is often a recessive gene as a result.
• Gain of function- change in the structure so that it gains new abnormal function. Usually a dominant mutation.
• Back mutation- a mutation which undoes another mutation
Types of Mutations by inheritance-
• Somatic mutations- Non Inheritable mutations
• Germ line Mutation- mutations which may be passed on to the next generation.
Causes of Mutations• Spontaneous Mutations- mutations without a cause, usually a mistake in translation.
• Induced mutation- mutations caused by a mutagenic agent such as radiation and certain chemical substances.
Evidence for evolution:
• Comparative Genomics- The similarities in genomes suggest a common ancestor, for example humans share 94% of our genome with chimpanzees. It is not simply sharing dna; its sharing the same retroviruses, chromosomal fusions, and even molecular biological relationships that represent occurences or changes in dna itself. Virtually all of which just happens to occur along the same dna chains amongst countless thousands of places it could have appeared. Each one of these findings in themselves represent INDIVIDUAL points of comparative data, they are separately arrived volumes of data that when compared with each other..overlap and match. Chromosomes, Dna, Retroviruses, Mitochondrial dna, molecular biology, fossil record ... all form a web of information that simply doesn't contradict itself. (Odin)
• "The simplest and most powerful evidence is provided by phylogenetic reconstruction. Such reconstructions, especially when done using slowly-evolving protein sequences, are often quite robust and can be used to reconstruct a great deal of the evolutionary history of modern organisms.This evidence does not support the rival hypothesis that genetic similarity of two species is the product of common functional or structural requirements, and not common descent (for example, if there is one best way to produce a hoof, all hoofed creatures will share a genetic basis even if they are not related). However, phylogenetic relationships also extend to a wide variety of nonfunctional sequence elements, including repeats, transposons, pseudogenes, and mutations in protein-coding sequences that do not result in changes in amino-acid sequence. While a minority of these elements might later be found to harbor function, in aggregate they demonstrate that identity must be the product of common descent rather than common function." -Wikipedia.
• The Fossil record- "It is possible to find out how a particular group of organisms evolved by arranging its fossil records in a chronological sequence. Such a sequence can be determined because fossils are mainly found in sedimentary rock. Sedimentary rock is formed by layers of silt or mud on top of each other; thus, the resulting rock contains a series of horizontal layers, or strata. Each layer contains fossils which are typical for a specific time period during which they were made. The lowest strata contain the oldest rock and the earliest fossils, while the highest strata contain the youngest rock and more recent fossils."- Wikipedia A great example of the fossil record is the horse which has an almost complete fossil record
• Comparative anatomy- Similar bone structure can be used to show the divergent evolutionary paths
• Vestigial organs and structures- Many species have a vestigial structures such as the human appendix and tail bone which indicate that a common ancestor made use of these structures
• Antibiotic and pesticide resistance- This is evidence of natural selection taking place, and it is an undeniable fact. Currently bacteria are becoming more and more resistant to antibiotics such as penicillin. A perfect example of this is golden staph where there have been reported cases of golden staph which is resistant to even the most potent antibiotics.
• Observed speciation- Speciation has been observed on a significant number of occasions which may be found
here under section 5.1
• Hybrids- Hybrids such as
ligers and
mules provides evidence of a common ancestor between two species.
Acceptance of evolution in the scientific community
In 2007 the Discovery Institute (the main "scientific body against evolution) claimed that 700 scientists had expressed support for intelligent design, although this may sound like a large number this actually means that roughly
99% of scientists support evolution. "And of the 700 'scientists' who have signed the Discovery Institute's letter, a vanishingly small number are biologists---most of them are physicists, engineers, computer scientists and the like. "
Spetznatz[youtube]Ty1Bo6GmPqM[/youtube]
"Additionally, the scientific community considers intelligent design, a neo-creationist offshoot, to be unscientific,[25] pseudoscience,or junk science.The U.S. National Academy of Sciences has stated that intelligent design "and other claims of supernatural intervention in the origin of life" are not science because they cannot be tested by experiment, do not generate any predictions, and propose no new hypotheses of their own."- Wikipedia
If I have made any mistakes or anybody sees improvements could be made to this thread please post suggestions or PM me.
Bibliography:
Observed Instances of Speciation- sourced from
www.talkorigins.orgSupport for evolution wikipedia-
http://en.wikipedia.org/wiki/Level_of_support_for_evolution#cite_note-61Wikipedia evolution page-
http://en.wikipedia.org/wiki/EvolutionSimplified explanation of evolution wikipedia page-
http://en.wikipedia.org/wiki/Introduction_to_evolutionJacaranda Biology 2008 Textbook-
Nature of Biology by Judith Kinnear and Marjory Martin
Evidence of common decent wikipedia page-
http://en.wikipedia.org/wiki/Evidence_of_common_descentFurther Reading/ Viewing -
Donexodus2's series "How evolution works" * props to Cycle4Fun for finding these fantastic resources which do a far better job than this thread
University of Berkley's Evolution 101 *props to Cycle4Fun for finding these fantastic resources which do a far better job than this thread
