3. Observed instances of beneficial mutations
Note: Because this category includes most of the case examples that are in other categories, we have not duplicated most of the other examples in this section.
Beneficial mutations of yeast in a low phosphate environment
In an experiment on evolutionary change,
yeast was placed in a low phosphate environment and scientists observed three beneficial mutations that helped the yeast adapt. The yeast was derived from an clonal line, which is a group of individual organisms with identical genomes. The
first mutation observed affected the permease molecule, and
allowed the yeast to absorb more phosphate, and thus it caused a boom in the population density. The
second mutation changed the yeast's phosphatase, which became more active. Finally, the
thread mutation allowed the yeast to clump together, and thus the population density grew further. (Francis & Hansche, 1972/1973) (Image Source 7)
Yeast adapts to a glucose limited environment via gene duplications and natural selection
As discussed above, in this experiment the hexose transport genes of the yeast duplicated and the duplicated versions mutated, which is an obvious addition of new material to the genome of the yeast.
These new genes allowed the yeast to more efficiently process glucose and thus be more likely to survive.(Brown et al., 1998)
Chlamydomonas adapts to grow in the dark
Chlamydomonas is an
algae that uses photosynthesis as its food source. Thus, it is ill adapted to grow in the dark. However, in an experiment conducted by Graham Bell, the organisms were selected in preference of those which grow in the dark, and a
fter several generations, chlamydomonas developed an ability to use acetate as a carbon source so effectively that the final strain was very adept at growth in the dark. (Bell)
Bacteria evolve to eat nylon
Researchers found a strain of
Flavobacterium in pools containing waste water from a nylon factory.
The strain had evolved to digest nylon, which is a recent modern man-made product.
The enzymes that allowed the bacteria to do so were novel and unlike any of those found in other strains of the same bacteria, and they do not aid the bacteria in digestion of any known materials besides nylon. Although the exact type of mutation is under debate, a large portion of the scientific community accepts the hypothesis that the mutation was caused by a gene duplication combined with a frameshift mutation.(Ohno, 1984) If this is so, this would also be an example of a mutation increasing genetic information in the genome. Gene duplication and frameshift mutations work like this example:
The genetic sequence may start as: THE CAT. The genetic sequence is duplication by a gene duplication mutation: "THE CAT" and "THE CAT". The duplicate is further transformed by a frameshift mutation: "THE CAT" and "HEC ATK", where 'K' is a shifted base pair from a adjacent gene sequence. Thus, information has been added. The genome has the new sequence "HEC ATK", which it had nothing like before.
Resistance to atherosclerosis
Resistance to atherosclerosis was documented in small population in Italy. The resistance was caused by a mutation in the angiotensin-converting enzyme gene, which affects the plasma levels in an individual.(Margaglione, et al., 1998)
E. coli evolves to hydrolyze galactosylarabinose
Scientists observed two mutations arise in a population of E. coli which allowed the bacteria to hydrolyze galactosylarabinose. (Hall and Zuzel 1980)
E. coli evolves to metabolize propanediol
In normal circumstances,
E. coli digest L-fucose and convert it into dihydroxyacetone phosphate and lactaldehyde, the latter of which is a waste product. Then, this waste product is converted into propanediol, which is then excreted from the cell. However, in a laboratory environment rich with propanediol, scientists observed
a mutation in E. coli that allowed it to digest the previous waste material and effectively use it as an energy source. (Lin and Wu 1984)
E. coli evolves to digest citrate
In a long term experiment on evolution with
E. coli, scientists observed
a mutation create a complex, new feature which allowed the E. coli to absorb citrate through its membrane. Because
E. coli is usually distinguished as a species which cannot digest citrate, this could also be considered a speciation event. To the left is an image of the flasks containing the
E. coli mutant from the experiment. (Lenski et al., 2008) (Image Source 8)
Klebsiella bacteria develop a new metabolic pathway to metabolize 5-carbon sugars
Several mutations that occurred in the bacteria
Klebsiella created an entirely new metabolic pathway in order to help metabolize exotic five-caborn sugars such as D-arabinose and xylitol. (Hartley, 1984)
Blowfly Insecticide Resistance
A simple mutation was observed to give insecticide resistance to blowflies. (Newcomb, et al., 1997)
Fungi evolves to harness high radiation levels in Chernobyl, Russia
Researchers found an interesting
new type of fungi directly inside the Chernobyl reactor core. As most know, Chernobyl, Russia was the site of an infamous nuclear disaster over 20 years ago.
The specific fungus appears to not only thrive in the dangerously radioactive environment, but the fungus actually harnesses the radioactive energy то survive. Evidence indicates that this new fungus evolved from the local fungi in the surrounding area.(Monaghan, 2008)
4. Observed instances of large morphological changes
Croatian Lizards change body shape to adapt to a new environment
Lizards of the species
Podarcis sicula from a nearby island were introduced by scientists to a new island previously uninhabited by scientists in 1971. Since then, several evolutionary changes have occurred.
The lizards now have larger heads and stronger bites. In addition, the population has evolved cecal valves, entirely new organs.(see below) (Herral, A. et al. 2008) (Image Source 9)
Anolis Lizards change body shape to adapt to new island environments
An excellent example of evolution in action is a 14-year experiment done with Anolis lizards.(Losos et al, 1997) A single species of Anolis lizards was spread across 14 Caribbean islands none of which had any previous lizard populations. Over the time of the experiment, the lizards each adapted to their respective environments. Several new species of lizards evolved.
The lizards each changed body shape in response to the flora in their environment. In fact, scientists were able to predict exactly how each lizard population would evolve before seeing the results.
Scientists estimate that this change was on the order of 200 darwins, which are measured units of evolutionary change. In comparison, the average rate observed in the fossil record is only 0.6 darwins.(Gingerich, 1983)
Galapagos Finches morphologically change in response to seed sizes
This is one of the most famous examples of evolution in history. In fact, during Darwin's visit to the Galapagos, the unique variation he observed among the finch beaks influenced his ideas on natural selection.
Since then, scientific observation has confirmed that Darwin's initial hypothesis was correct; the finches do evolve in response to the size of available seeds. A large study found that over the years, the size of beaks in the population Geospiza fortis fluctuated in response to the size of the available seeds.(Grant 2002) (Image Source 10)
Autralian snakes adapt to introduction of poisonous toads
The species of toad
Bufo marinus was introduced to Australia in 1935. As invasive species, they have quickly spread and today are quite numerous. This is especially due to their toxic flesh, which kills any predator attempting to grab one to eat.
Since then, at least two species of snakes have evolved smaller heads, and thus smaller bites, in response to the toads. Snakes with smaller heads could not eat the large toads, and thus did not die from the poisonous flesh, and were capable of eating other smaller, harmless species. (Phillips et al., 2004)
Change in size of the bony armor of Stickleback fish
Researchers isolated
specific genetic mutations in a population of stickleback fish that change the size of the fish's bony armor enormously. The photo to the left shows a stickleback with minor bony armor (bottom), and one with an enlarged plate (top).(Kingsley 2004 and 2005) (Image from source)[DOUBLEPOST=1408917012][/DOUBLEPOST]
6. Observed evolution of a multicellular organismAS
Evolution of a new multicellular species from unicellular Chlorella
When a predator was introduced to the environment of the unicellular
Chlorella algae in a lab test, scientists observed the
algae cells bond together in colonies, and eventually became an entirely new multicellular species. One could even argue that this change extends past the species level. In the image to the left, FC is the unicellular chlorella algae, Oc is the predator introduced to the environment, and CC is the new multicellular algae.
This is not simply a "cell colony", but a new multicellular organism. The multicellularity was achieved by a mutation that fused the cell wall of the mother cell and its daughter cell together. Because these cells are thus dependent upon each other for survival, the new organism is multicellular and not a simple bacterial colony.(Boraas et al., 1998) (Note: The Image is also from this source.)
7. Observed endosymbiosis
Endosymbiosis is the evolutionary theory that the organelles in eukaryotes were once separate prokaryotic organisms which were taken in by another prokaryote. This effectively explains the evolution of eukaryotes. This old theory has recently been shown possible by an observed case of endosymbiosis in the laboratory. In this specific case, the unicellular predator
Hatena absorbed the algae producer
Nephroselmis. I
nstead of digesting Nephroselmis, the algae grows inside Hatena, and begins to produce food for both of the organisms. Hatena no longer needs a mouth, and thus this feature completely disappears. Effectively these two prokaryotes form a new eukaryotic cell. On the left is a picture of
Hatena with
Nephroselmis and without (Okamoto, 2005). (Note: The image is also from this source)
Microbiologist K.W. Jeon has done extensive research documenting an example of observed endosymbiosis in the laboratory. His experiment consisted of infecting a population of amoebae with a bacterial strain. While the majority of the amoebae died from the infection, some of the bacterial cells remained within the amoebae cells. Over time, J
eon proved that the amoebae eventually grew dependent on these bacterial cells, effectively creating a newly endosymbiotic eukaryote (K.W. Jeon 1972, 1977, 1987, 1995).
8. Mutation rates
Below we have listed the results of several studies on mutation rates. These results show that mutations aren't extremely rare, and beneficial mutations aren't as uncommon as one might think. Additionally, note that although beneficial mutations are a minority, harmful mutations are selected out of a population and thus have no lasting effects.
A. Most mutations are neutral, and have no effects. Only approximately 1 in 15 mutations have any effect.(Perfeito et al. 2007)
B. 12% (3 out of 26) of random mutations in a strain of bacteria improved fitness in a particular environment.(Remold and Lenski 2001)
C. Another study found that 10% of functional mutations in
E. coli were beneficial. (Perfeito et al. 2007)
D. Another study approximated that there are around 64 mutations in each human zygote.(Drake et al. 1998)
Human evolution
Obviously, the human species is still evolving, and humans have changed quite a bit since our species first arose. We already talked about the evolution of lactose tolerance in a previous post, but there is quite a bit more to cover. Thus, this blog post is all about evolution in humans from the present and recent past.
Brain Evolution
Evans et al. 2005 found that a
gene named Microcephalin regulates brain size in humans. A specific variant of this gene first arose in humans about 37,000 years ago, and has since for been positively selected for in the human population. This study provides strong evidence that the human brain has been undergoing rapid evolution in the recent past.
The Evolution Of Lactose Tolerance
It may come as a surprise to many people living in the Western world that
the majority of adults on Earth are to some degree lactose intolerant. After all, we take lactose tolerance largely for granted in societies dominated by Europeans; in fact, milk and milk based products are essential staples of the daily diets of these countries. From breakfast to dessert, butter, milk, and cheese come with the meal.
However, those with complete lactose tolerance are in the global minority, and are in fact mutants. A few single nucleotide( nucleotides are individual units of DNA) changes confer lactose tolerance through adulthood in European and a few African populations with the mutations seen below:
(Tishkoff et al. 2007) (Image adapted from source)
This is merely a successful example of evolution at the most basic level: a beneficial mutation arising naturally and successfully spreading throughout a population.
Sickle-cell and Malaria Resistance
Sickle-cell is a human blood disorder in which red blood cells take on a sickle shape instead of the normal round donut shape of red blood cells, and is caused by a single point mutation. While having both of the recessive sickle-cell alleles can cause several life-disrupting complications,
being a genetic carrier of the recessive allele has a positive advantage in that it confers some resistance to malaria. Thus, the allele has been positively selected for in recent times throughout Africa, where malaria is extremely common and poses a significant threat. (Kwiatkowski 2005)
Resistance to Heart Disease
Several carriers of a mutant allele called Apo A-1 Milano have been found in Italy. This allele has been shown to confer resistance to Heart Disease even if cholesterol levels of a carrier are extremely high.(Long 1994; Weisgraber et al. 1983)
Resistance to HIV in Humans
Resistance to HIV has been found to be conferred by a mutation in some Caucasian individuals with a mutant form of a gene called CCR-5. (Samson et al. 1996)
Tibetan Adaptations to High Altitudes
Considered to be one of the fastest known examples of human evolution in recent times,
several mutations in Tibetans have allowed them to adapt and survive at high altitudes. About 30 different genes which regulate metabolism and oxygen have specifically undergone natural selection to confer these beneficial changes. (Yi et al. 2010)
И Мики дали гореневеденото соодветствува со твоето тврдење дека:
1. Денешните здрави науки ја растурија еволуционата философија, која своето опстојување го има само во образовниот систем и низ медиумите, но не и надвор од нив.
2. Времињата во кои еволуцијата беше „монополистичка„ вистина, веќе се се зад нас.[DOUBLEPOST=1408917095][/DOUBLEPOST]
И сега, како ќе го опишеш начинот на кој ДНК поприма нови инфомации, кои, пренесувајќи се на наредното поколение, дава еволутивен скок во облик од ново битие?
Читај, ти посочив линкови. Не можам сега да одвојам толку многу од моето време за да те учам.