G10 Evidence for Evolution Flashcards
The age of fossils can be determined through different methods, and the most commonly used ones are relative dating and absolute dating.
refers to the method of determining the age of a rock layer and the fossils within based on sequences of events
Relative dating
four major laws in the field of geochronology
law of original horizontality
law of lateral continuity
law of superposition
law of crosscutting
which merely states that depositions for the layers are usually in a horizontal manner
law of original horizontality
which states that layers spread out laterally until they thin at the edges of the area, or into a different rock layer segment
law of lateral continuity
which states that the oldest rock layers are usually found under newer rock layers
law of superposition
which states that rocks and other features are younger than the layers that they intrude into
law of crosscutting
It gives a numerical estimate of the age of the object being tested
This method relies on the decay of certain elements through their half-life
The half-life of an element is the time it takes for that element to be reduced to half of its original amount
absolute dating
Absolute dating will usually involve taking the estimated age of a rock layer, or sometimes, even the fossil itself.
The most commonly used elements for absolute dating are carbon-14 with a half-life of 5,730 years, and potassium-argon dating with a half life of 1.3 billion years
fossil classification
mold fossils
trace fossils
true form fossils
cast fossils
is formed when an impression of an organism is made over a substrate. Most of the time, this creates a concave image (or a “negative”) of the organism in the substrate
mold fossil
is the fossilized remains of the traces of an organism
examples of fossils include remains of footprints, nests, and the like
trace fossil
is the fossilized remains of a part or the entire organism. Examples include dinosaur bones and insects trapped in amber
true form fossil
can be formed alongside a mold fossil
occur when a substance fills in the mold fossil, which forms a replica of the organism from the cast
cast fossil
A fossil record is derived from the discovered fossils all over the world. It shows the history of life as documented by fossils.
are fossils of organisms that are used for determining the age of surrounding rocks, and consequently, the age of the fossils within these rocks
index fossils/guide fossils
four criteria for classifying a fossil as an index fossil
abundance of the fossil
ease of identification
geographic range
temporal range of the fossil
From fossils, scientists were able to construct an evolutionary tree based on the similarities between specific structures of organisms.
Amphibians are known to have descended from fish, and the fossils of these fish have been found. Scientists based the evolutionary tree they created on the development of the different structures found, as well as the change from fins to legs.
Another example is the Pakicetus which is considered to be one of the ancestors of modern whales. They are land animals with long skulls and large carnivorous teeth, and their skulls strongly resemble those of the living whales.
are body parts of different organisms with similar forms but the functions are not necessarily the same
This implies that these structures may come from the same sources but have possibly evolved as a result of different pressures.
Homologous structures
refer to the repeating structures found within one organism
serial homology/homotopy
Serial Homology
Also known as homotopy, serial homologies refer to the repeating structures found within one organism.
These structures perform roughly the same function but may have different specializations.
An example of a serial homology is the presence and structure of human vertebrae.
The Implications of Homologous Structures in Evolution
Homologous structures suggest descent from a common ancestry.
Taking a look at the different functions of homologous structures also gives a perspective of how these structures came to be.
The specific modifications of these structures may show what environmental pressures these animals have faced which led to the adaptation of these modifications.
The limbs of tetrapods (amphibians, reptiles, birds, and mammals) share the same arrangement of bones. They are all composed of the radius, ulna, and humerus. However, these limbs serve different functions.
The upper limbs of bats are for flying, whereas those of humans are used for grasping. In whales, the upper limbs are found in the flippers, which are used for movement in the water.
are ones that have the same function but have evolved differently
Analogous structures
which are traits shared by a group of species but are not present in their common ancestor.
These structures imply an independent development of these structures within these animal groups.
homoplasies
The Value of Analogous Structures in the Study of Evolution
While analogous structures and homoplasies do not give much perspective as to how related lineages have evolved, looking at them can also give a view of the environmental pressures that organisms had to overcome, much like the view the homology gives.
Analogous Structures
The wings of insects and birds both have the function of flight but these traits arose independently from each other.
Homoplasies
An example would be the development of structures that animals use for sight, which is found in many groups but not all found in their common ancestors.
are organs that are present in an organism but do not perform any particular function
Vestigial structures
Vestigial structures are organs that are present in an organism but do not perform any particular function.
Some examples of vestigial structures are the tailbone and appendix in humans.
The Implications of Vestigial Structures in Evolution
Vestigial structures predict the organism’s evolutionary past, suggesting common ancestry with species that have similar structures but are still functioning.
Whales have retained their vestigial hind limb, which is disconnected from the spine.
This vestigial structure is considered to be a remnant of their time on land.
The use of these structures in looking at the evolution of whales, as well as structures observed in the fossil record, have shown a clear picture of the evolutionary history of whales.
The vestigial hind limbs of snakes, much like the vestigial hind limbs of whales, gives a view of how these organisms might have evolved.
Scientists believe that snakes descended from lizards over a hundred million years in the past.
More recent genetic evidence also supports this claim, stating that snakes and lizards are indeed very closely related. In fact, snakes and lizards belong to the same reptilian group known as Squamata
Homologous structures are body parts of different organisms with similar forms but the functions are not necessarily the same. Homologous structures suggest descent from a common ancestry.
Analogous structures are ones that have the same function but have evolved differently.
Vestigial structures are organs that are present in an organism but do not perform any particular function. Vestigial structures predict the organism’s evolutionary past, suggesting common ancestry with species that have similar structures but are still functioning.
Modern studies regarding the evolutionary history of organisms most often use genetic data to infer the relationship between species and groups of organisms.
This is in contrast with earlier studies that purely used morphological and anatomical features for looking at evolutionary relationships.
Morphology and anatomy, along with genetics, are used side-by-side in order to properly gain an insight on how organisms are related.
is a branch of biology that studies genes, heredity, and genetic variation
provides a more complex evidence of evolution
Genetics
a universal genetic message
This genetic message is the same in all organisms on earth. Therefore, it supports the idea that there is a common ancestor for all life forms.
triplets of DNA nitrogen base sequences that code for specific amino acids
details how genetic information is processed into a usable product.
This concept can be summarized into the flow of information, wherein DNA is transcribed into mRNA, and mRNA is translated in order to form proteins.
The Central Dogma of Molecular Biology
The Universal Genetic Code
There is a universal genetic message—the triplets of DNA nitrogen base sequences that code for specific amino acids.
This genetic message is the same in all organisms on earth. Therefore, it supports the idea that there is a common ancestor for all life forms.
The Central Dogma of Molecular Biology details how genetic information is processed into a usable product.
This concept can be summarized into the flow of information, wherein DNA is transcribed into mRNA, and mRNA is translated in order to form proteins.
Since organisms that are closely related share much of their genetic code’s sequences and identity, this means that many of the products of their genes are also shared. This leads to the many physical similarities between closely related species.
Genetic Similarity and Evolution
Organisms with similar characteristics mean that there is a chance that they have shared genes. The study of genetics looks at the similarities in the DNA of organisms in order to infer the possible evolutionary relationship between them.
For example, approximately 96% of human genes are similar to those of chimpanzees, and 90% of these genes are similar to those of cats.
These percentages do not prove that humans evolved from chimpanzees or cats. However, they mean that humans, chimpanzees, and cats may have shared a common ancestor in the past.
The differences between the genes correspond to how long ago the genetic lines between the organisms have changed.
Mutations and Evolution
Certain changes that arose from mutations can be used to determine the evolutionary relationship between species.
For example, suppose that you are looking at three closely-related species and trying to understand which of the three are more closely related.
Suppose that two of them share the same changes, then the chances of these two being more closely related to each other are higher compared to the other one that does not have the change from the mutation.
Mutations can also give an estimate of when divergences from certain lineages have occurred.
Take the example of the three species above again. There are multiple possible situations that can arise regarding their evolutionary history if the timing is taken into account.
One is that the mutation first occurred in the ancestor, and these were passed on to the two species while the other one diverged.
Another possibility is that the ancestor did not have the change from the mutation, but a divergence occurred which eventually led to the formation of the species with the changes from that mutation.
Mutations must persist for evolution to take place.
One instance that this may happen if the phenotype that is the manifestation of these mutations can bestow an adaptive advantage to the organisms that possess them, thereby increasing their fitness and reproductive success.
A higher reproductive success for these organisms means that they have a chance of successfully passing on these genes, including the newly-mutated ones.
Methods in Genetics
DNA Extraction
DNA Amplification
Genetic Sequencing
Analysis
involves the isolation and retrieval of a sample of the organism’s DNA.
The sample collected must be pure, meaning the DNA must come from the organism and that organism alone.
DNA extraction
is needed in order to increase the amount of material in the sample.
effectively increases the amount of DNA by creating exact copies of the desired sample. As shown in the figure below, just after the 35th cycle, 68 billion copies of DNA are already made.
DNA amplification
The amount of DNA extracted is usually small, so a method known as DNA amplification is needed in order to increase the amount of material in the sample.
DNA amplification effectively increases the amount of DNA by creating exact copies of the desired sample. As shown in the figure below, just after the 35th cycle, 68 billion copies of DNA are already made.
In most cases, specific genes are used and analyzed when trying to determine evolutionary relationships.
When amplifying DNA, these genes are usually targeted so that more copies of the desired gene is created. These genes are usually the ones that are sequenced and analyzed.
involves the identification of the individual nucleotides that make up the gene
Genetic Sequencing
Certain softwares are used in order to check the similarity of the nucleotide sequences from the organism compared to other organisms. The more similar they are, the more likely that they are related to each other.
Analysis
Modern studies regarding the evolutionary history of organisms most often use genetic data to infer the relationship between species and groups of organisms.
Genetics is a branch of biology that studies genes, heredity, and genetic variation. Genetics provides a more complex evidence of evolution.
Organisms with similar characteristics mean that there is a chance that they have shared genes. The study of genetics looks at the similarities in the DNA of organisms in order to infer the possible evolutionary relationship between them.
One of the most commonly used methods in looking at evolutionary relationships from a genetic standpoint would be through the use of DNA.
Genetic sequencing involves the identification of the individual nucleotides that make up the gene
once contained the vast majority of the world’s landmasses. It formed more than 300 million years ago and broke up around 175 million years ago.
supercontinent of Pangaea
The supercontinent of Pangaea had two major regions of land, which were
Gondwana
Laurasia
Pangaea was surrounded by the superocean known as
Panthalassa
refers to the movement of populations across a geographical location, most usually a barrier
Dispersal
occurs when populations are isolated by the appearance of geographical barriers that make it impossible for these populations to continue interbreeding.
Vicariance
