Evolution in Beak Size

Evolution generally happens over hundreds of years and is usually not noticeable in one’s lifetime. The evolution of beak shape in Galapagos finches is an exception to this. The Galapagos finches have a variety beak shapes. They range from long and skinny to deep and thick. Their beaks are adapted to the type of seed they eat. The small beaked finches feed off small fleshy seeds. The thick beaked finches feed off tough thick seeds. The range of beak morphologies directly reflects the foods they eat. The sizes of these beaks are generally pretty even. During years of extensive drought a shift in beak size can be seen. The drought has to occur over a few generations for the results to be seen. The thick beaked finches can eat tough seeds that are resistant to drought. These birds are unaffected by drought. The thin beaked finches often struggle during the drought years. Their small fleshy seeds become very sparse. Their beaks don’t allow them to eat the tough seeds and the birds often die as a result of starvation. Their death means that they cannot pass on their thin beaked genes. The thick beaked finches are healthy and can reproduce. Their thick beaked genes are passed along, creating a shift. The shift is towards thicker beaks. The thick beaked finches are able to continue to pass along their genes while the thin beaked finches continue to struggle. There are finches with intermediate beak size and are also able to pass along their genes. Over a few generations you are able to see a shift toward thicker beaked finches.

http://www.truthinscience.org.uk/tis2/index.php/component/content/article/53.html

For more information:

http://www.truthinscience.org.uk/tis2/index.php/component/content/article/53.html

http://www.pbs.org/wgbh/evolution/library/01/6/l_016_01.html

Age Structures

Age structure diagrams are tools that we use to determine how a community is growing. Developing and developed countries tend to have very different age structures. The population is divided into age brackets. For example ages 0-2, 3-5, and so forth. Then a census is taken to see how many individuals in the country are in each bracket. In the United States a census is taken every 10 years. It can be a very tedious process collecting the population’s ages. The information is then further divided into males and females. Once the population is tallied it can be described by age structure, or the portions of the population in each age class. There are three types of age structure: rapid growth, zero growth, and negative growth. The rapid growth structure has a very wide bottom and it progressively thins out. It looks similar to a triangle. This is considered rapid growth because there are many individuals in the reproductive stage of their life that will continue to contribute to the growth of the population. Countries that have this trend include Nigeria and Guatemala. Zero growth means exactly what it sounds like. There is not any growth occurring in the country. There are equal numbers of individuals in each age bracket. Spain and Austria have a trend like this. The third structure is Negative growth. In this structure there are less individuals in their adolescents and reproductive ages than there are those who are past reproduction. This means that the country will not grow and actually decrease in size in the next few years. Germany and Bulgaria have a trend like this. These structures can give insight into how a country is growing.

http://skepticlawyer.com.au/page/2/

For more information:

http://esa21.kennesaw.edu/activities/populationage/populationage.pdf

http://people.oregonstate.edu/~muirp/agestruc.htm

The origin of Homo sapiens

The origin of modern Homo sapiens is very controversial. Some early species, such as Homo ergaster, Homo erectus, Homo neanderthalensis, Homo heidelbergensis, and possibly even Homo antecessor, are all possible ancestors of the species Homo sapien. Recent studies have shown that Homo sapiens most likely descended from populations in the Homo ergaster and Homo erectus group. Modern Homo sapiens first appeared in the fossil records about 100,000 years ago in Africa and Israel. Later fossils were found also in Europe and Asia.
Scientists have debated three different models for explaining the origins of modern humans. These are the African replacement model, the multi-region model, and the assimilation model.
The Recent African Origin model was given a huge boost in 1987, when a paper published in the scientific journal Nature, Mitochondrial DNA and Human Evolution, rocked the palaeoanthropology world. It showed that part of our genome, inherited only through mothers and daughters, derived from an African ancestor about 200,000 years ago. This female ancestor became known as Mitochondrial Eve.Although the paper was contested, the results strongly supported the views that the Natural History Museum’s human origins expert Chris Stringer and others had been developing that we had a recent African origin. In the following decade, more genetic data both from recent human people and Neanderthal fossils were collected supporting the Recent African Origin model. The idea gained momentum and with it the view that when modern humans began to leave Africa around 60,000 years ago they largely or entirely replaced other archaic human species outside the continent.
The Multi-regional model, by contrast, put forward parallel lines of evolution in each inhabited region of Africa, Europe, Asia and Australasia, glued together by interbreeding across the human range.Under this model, there was no real origin for the modern form of Homo sapiens. A feature like a chin might have evolved in a region such as Africa and spread through interbreeding, followed by selection if it was an advantageous characteristic. Another feature, like our high forehead, might have evolved elsewhere and then spread through interbreeding.
Another group of scientists embraced a third theory: the Assimilation model. Like the recent African origin model, this gave Africa a key role as the place where modern human features evolved, but it imagined a much more gradual spread of those features. Under this view, Neanderthals and archaic people like them were assimilated through widespread interbreeding. This meant that the establishment of modern human features occurred via a blending of populations rather than a rapid replacement.
Information acquired from: http://www.nhm.ac.uk/nature-online/life/human-origins/modern-human-evolution/where/index.html
So which of these models is right? It is unknown. Though there are many hypotheses and evidence of many different results, scientists do not fully understand the origins of the species Homo sapien.
For more information about this topic:
http://anthro.palomar.edu/homo2/mod_homo_4.htm

Endosymbiosis

Endosymbiosis is discussed in chapter 15 of the textbook as an explanation for how organelles were formed.  Chloroplasts and mitochondria serve as prime examples for this theory. Both have their own DNA present in the organelle that is not present in the nucleus of the cell and a double membrane that could be formed by the bacteria. Both organelles also have their own form of replication within the cell that is similar to bacteria. The formation of chloroplasts and mitochondria are the result of secondary endosymbiosis.
Even though endosymbiosis is called a theory does not mean that it is completely accepted. There is evidence for but there is also against the theory. The double membrane that is usually an argument for the endosymbiotic theory but some argue it because the differences between the mitochondrial membranes and the membranes of bacteria are different. Another point that is argued is the form of replication that mitochondria have begins at a different location than in bacteria. The largest argument against the theory is the lack of a good mechanism for how gene transfer could have occurred between the organelle and the cell, especially during the beginning of the process.
I find it interesting how there can be a universally accepted theory that can still be debated. There are arguments for and against. I would go with the proendosymbiosis theory but i enjoyed learning about arguments against the theory.


http://www.evolutionnews.org/2012/01/on_the_origin_o054891.html
http://learn.genetics.utah.edu/content/begin/cells/organelles/
http://www.biology.iupui.edu/biocourses/N100/2k2endosymb.html

Humans and Chimps

The idea that humans evolved from within the apes has many people doubting evolution. They can not fathom that humans and primitive apes are related to one another. Evolutionists have been slowly proving this, and it is looking more and more like a possibility. Through the use of morphological and molecular evidence apes and humans are being linked. Humans are a fairly young species. In fact humans and chimpanzees shared a common ancestor about 5.4 million years ago. This number is fairly small in the big scheme of evolution. The fossil evidence linking humans to apes is relatively thin, however, it is getting better. With every new discovery we get closer to linking humans and chimpanzees. The bones of early humans can tell us a lot. For example, Australopithecus gahri, Australopithecus africanus, and Australopithecus afarensis had skulls with small brain cases and large protruding faces. Examining the hips, knees, feet, and vertebral column suggest that they walked in an upright position. They did not use their arms and did not drag their knuckles. Of the few intact skulls that have been found the size of the brain case can be very helpful when determining where the skull is placed in a lineage. Humans today have very large brain cases and the earliest skull has a very small brain case. Humans can be seperated from chimpanzees and other hominins by looking at five distinct things. There five things are: bipedalism, skulls, child dependency, tools, and teeth. No hominin found to date has the exact same characteristics as humans. While other parts of the body such as the hips can be evidence into the lives of the species, analyses preformed today rely mainly on the skulls and teeth. The phylogenetic relationships among the species of fossil hominins have not been definitively established. Many still are devoting their lives to finding the missing piece of the puzzle. There are still gaps in the phylogenetic tree that are critical to linking humans and chimpanzees.

http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_5.htm

Other helpful links:

http://anthro.palomar.edu/hominid/australo_1.htm

http://www.baskent.edu.tr/~zuyen/courses/psk104/03-EarlyHominins.pdf

Vicariance Events

Vicariance events are speciation events where a species' distribution becomes segmented and the separated populations evolve due to different selecting factors, causing the populations to become unique species. There are numerous ways that this can occur: by something as long and slow as the rising of a mountain range or the separation of Gondwana to something as quick as an erupting volcano. Many endemic species are due to vicariance and the separation of Gondwana. The island of Madagascar is an excellent example because of its location during the separation process; it was in the middle of two larger land masses that would eventually become the four southern continents (South America, Africa, Antarctica, and Australia) and another land mass that would become India. This make it easier to understand how Madagascar can have only one extant freshwater fish species who's closest relative is located on nearby Africa, but all the other freshwater species present have their closest relative on India and Australia.



Vicariance events do not have to be as dramatic as a super-continent dividing. It depends on whether the event makes it where gene flow can not occur; we have looked at examples where two populations have been separated but are still the same species because there is still gene flow between the populations like with the water snakes around Lake Erie. The gene flow between them kept one color morph of the snake from becoming its own unique species.

http://www.sciencedaily.com/releases/2012/08/120829151239.htm
http://evolution.berkeley.edu/evolibrary/news/091001_madagascar

Some information about hybridization

Can hybridization create new species distant from the parental species? If hybrid offspring occupy habitats that are different from the habitats that their parents live in, it is possible that the hybrid offspring will have higher fitness in the novel habitat than either of the parent species. So how are hybrids created, and why would this event occur? There are two types of hybrids (which are both self explanatory): man made hybrids and natural hybrids. Hybrids are created when two closely related species are able to breed. The best way I can explain it is through an example. Though Napoleon Dynamite was a comedy movie, Napoleon was not joking when he was saying there was a such species called the "liger." A lion and tiger hybrid. I always thought it was a joke, but these things actually exist, along with hundreds of crazy and bizarre others. Upon doing research for this blog post, I stumbled upon a fun page titled the 20 coolest hybrid animals, which I will post a link at the bottom of this post just for fun. Also at the bottom is a link to a page titled blogging about bonking, which I thought was hilarious, but it has a lot of information about hybrids and how they occur.

http://www.buzzfeed.com/toyota/the-20-coolest-hybrid-animals-3d8x

http://howanimalsdoit.com/2012/01/07/the-science-and-magic-of-hybrid-animals/