Natural Selection Flashcards
Natural Selection
Charles Darwin’s theory of natural selection proposed that all species have evolved from simple life forms that first appeared on Earth more than three billion years ago.
Genetic variation
Different individual animals in a population (or species) have different combinations of genes (show genetic variation).
Survival of the fittest
Individuals that are best adapted to the environment will have a greater chance of survival.
Successful breeding
Individuals with the best chances of survival are the most likely to breed successfully (because they survive).
Best characteristics survive
The characteristics responsible for the greater chance of survival are more likely to be passed on to the next generation.
Charles Darwin developed his theory of evolution whilst
aboard the HMS Beagle on an expedition to the Galapagos Islands. He built up evidence to support the theory of natural selection and in 1859 he published his ideas in “On the Origin of Species”.
Controversy around Natural Selection
At the time, Darwin’s ideas were met with significant opposition from the scientific community.
Genes yet to be discovered
At the time, genes had not been discovered and Darwin was unable to suggest a method for the passing of characteristics between generations (from parent to child).
Inconclusive evidence
There were scientists that regarded the evidence presented by Darwin as inconclusive.
Religion
Natural selection challenged the common belief that God created the natural world.
Alfred Russel Wallace
Most people think that Charles Darwin was alone in thinking about natural selection. In fact, Alfred Russel Wallace wrote to Darwin in 1858, expressing his similar thinking.
Island research
Both had spent a significant amount of time on islands.
This decision helped their research on evolution because the isolation of island populations leads to enhanced speciation (the formation of new species) rates.
Joint writings
1858, the two combined their great minds to produce joint writings.
Competition
After the two had produced joint writings, Darwin accelerated the publication of ‘On The Origin of Species’ to be the first of the two to publish.
It is a common misconception that
Darwin was alone in pioneering the thinking behind natural selection. In fact, Alfred Russel Wallace wrote to Darwin in 1858, expressing his similar thinking. This caused Darwin to accelerate the process of publishing his book.
Impacts of the Theory of Evolution
Evolution is the gradual change of inherited characteristics of biological populations over time. It is usually driven by natural selection. The theory of evolution has greatly affected modern biology.
Genetics
Scientists later discovered exactly how traits are inherited; through genes.
Genetics is now a huge area of biology
Which area of biology wouldn’t exist without the theory of evolution?
Genetics
Evolution and Speciation
Evolution is the gradual change of inherited characteristics of biological populations over time.
The Evidence for Evolution
The discovery of genes as a mechanism (way) to inherit characteristics and create variance supported the theory of evolution.
Antibiotic resistant bacteria
Natural selection neatly explains this phenomenon: Bacteria reproduce rapidly. Mutations occur during reproduction. If a mutated bacterium is resistant to antibiotics, it will survive exposure to antibiotics and go on to reproduce. This bacterium will represent the original ancestor of a new resistant strain.
Fossils
Fossils show the gradual changes in organisms over vast periods of time.
Resistant Bacteria
Bacteria reproduce rapidly. Mutations occur during reproduction. This means that bacteria can evolve rapidly.
Example
An example of an antibiotic resistance bacteria is MRSA.
Reducing new resistant strains
Measures must be taken to reduce the emergence of new antibiotic resistance strains: Doctors should avoid prescribing antibiotics unnecessarily, for example for treating non-serious or viral infections. Patients must finish a course of antibiotics to make sure that all of the bacteria are killed. The use of antibiotics in agriculture (for example, cattle feed), should be restricted.
Resistant strain of bacteria
If a mutated bacterial pathogen is resistant to antibiotics, when a person is treated with antibiotics, the bacteria will survive and go on to reproduce. This bacteria is the original ancestor of a new resistant strain.
This bacteria will spread, as there will be no treatment for it, and people are not immune to it (as they were previously treated with antibiotics).
Antibiotics
The development of new antibiotics is a slow and costly process.
It struggles to keep up with the emergence of new strains.
Bacteria reproduce and evolve
Rapidly
To reduce the risks of
bacterial resistance, doctors should avoid prescribing antibiotics unnecessarily, patients must finish a course of antibiotics, and the use of antibiotics in agriculture should be restricted.
Pentadactyl Limbs
By comparing similar structures in similar animals, we may be able to prove that these organisms have evolved from the same organism. An example of this is the pentadactyl limb (which means five digits or fingers).
Many vertebrates (animals with backbones) have a very similar bone structure, even though their limbs looking very different from the outside. This is because organisms have evolved to different lifestyles in different places.
How can looking at similar structures between organisms be used to provide evidence for evolution?
By comparing similar structures in similar animals, we may be able to prove that these organisms have evolved from the same organism.
An example of this is the pentadactyl limb (which means five digits or fingers).
Another example is that many vertebrates have a very similar bone structure, even though their limbs looking very different from the outside.
Which animals have pentadactyl limbs?
Looking at the skeletons of animals shows that most vertebrates (animals with backbones) have pentadactyl limbs. The hooves of horses, flippers of whales, wings of birds and the feet of frogs and lizards all have five digits.
Fossils
Fossils are the remains or traces of ancient life. Fossils are found in rocks and have been preserved by natural processes.
Mineral replacement
Hard parts of organisms are gradually replaced by minerals as they decay slowly, creating a rock-like substance. When the surrounding sediment turns to rock, the teeth-shaped mineral structure remains distinct (different).
Preservation when decay is not possible.
Where decomposers cannot act, preservation is possible.
Decomposers cannot operate in glaciers (extreme, low temperatures) and peat bogs (extreme acidity).
Hardening soft materials
The hardening of soft materials can produce casts or impressions, such as footprints.
For example, clay hardens around an organism that is buried within it. This organism then decays, leaving behind a cast of itself.
Fossils are the remains or traces of
ancient life, which are found in rocks and have been preserved by natural processes.
Human Evolution
Fossils can be dated, so scientists have evidence for what organisms looked like at different periods in time. Comparing the fossils indicates how humans have changed over time.
Ardi
The oldest fossilised human remains are of Ardi (from the species Ardipithicus ramidus) dating back 4.4 million years ago.
Lucy
Another fossil was found called Lucy (from the species Australopithecus afarensis), which has been dated at 3.2 million years old.
Leakey
There have been more recent discoveries by of human fossils by an archaeologist (fossil-hunter) called Leakey, who discovered fossils from 1.6 million years ago.
Stone Tools
Stone tools show how humans have evolved: the more complex the tools used, the more developed the brain of the user. This can be linked with the fossil record.
Basic tools
Very basic tools have been found dating back to 2.6 million years ago, but these were mainly flakes of rock with a sharp edge.
Complex tools
At around 1.6 million years ago tools became more sophisticated and abundant.
Dating tools
Carbon dating a stone tool does not tell us how old the tool is, it only tells us when the rock was originally formed. To determine when the stone tool was in use:
Determine how deeply the artefact was buried. The deeper the object was stored, the older the object.
Use known dates of other items or fossils found at that level.
Compare the design to other stone tools that are already dated.
Classification Systems Classification groups organisms by comparing their similarities and differences:
3-domain system
Carl Woese proposed the 3 domain system. This classifies organisms based on chemical analysis.
The 3 domains are:
Archaea - primitive bacteria.
Bacteria - true bacteria.
Eukaryota - organisms possessing complex sub-cellular structures (protists, fungi, plants & animals).
Traditional (Linnaean) classification system
The traditional classification system, devised by Carl Linnaeus, categorises organisms based on their structure and characteristics. He created 7 different groups - Kingdom, Phylum, Class, Order, Family, Genus, Species.
Traditional (Linnaean) Classification System
The traditional classification system, devised by Carl Linnaeus, categorises organisms based on their structure and characteristics. Linnaeus classified biodiversity into seven different groups. The diagram shows the groups in descending order of size.
To remember the order of the Linnaean classification (in descending size order): King Prawn Curry Or Fried Greasy Sausage.
Which species are being named?
Tiger: Panthera tigris
Lion: Panthera leo
Human: Homo sapiens
The Three-Domain System
The ‘three-domain system’ was proposed by Carl Woese and classifies organisms based on chemical analysis.
Archaea
Primitive bacteria, many of which are extremophiles (i.e. live in extreme environments).
Bacteria
True bacteria
Eukaryota
Organisms that possess complex subcellular structures (e.g. protists, fungi, plants and animals).
