Evolution Flashcards
(14 cards)
Hypothesis of Evolution in the History
• Long before Darwin was born, several Greek philosophers suggested that life might
have changed gradually over time.
• Aristotle (384-322 B.C.), who greatly influenced early Western science, viewed species
as fixed (unchanging).
• Through his observation of nature, he recognized certain «affinities» among organisms.
• Aristotle concluded that life-forms could be arranged on a ladder, or scale, of increasing
complexity, later called the «scala naturae» (scale of nature)
Lamarck explained his finding using two principles:
1) use and disuse or the idea that parts of the body that are used extensively become larger and stronger, while those are not used deteriorate (e.g. Giraffe stretching
neck)
2) inheritance of acquired characteristics that stated that an organism could pass these modifications to its
offspring
A Darwinian view of life
Charles Darwin (1809-1882) developed his revolutionary proposal over time, influenced by the
work of others and by his travels
• HMS Beagle 1831-1836
Darwin observed many examples of adaptations
• inherited characteristics of organisms that enhance their survival and reproduction in specific environments.
• current species are descendants of ancestral species
1836 Darwin returned
1844 main manuscript
• worried about the acceptance of his ideas
• Wallace developed similar ideas independently
• Pushed Darwin to publish his work
The theory of evolution by natural selection is attributed to Darwin because he developed his ideas earlier and supported the theory much more extensively
1858 Wallace’s paper and extracts of Darwin’s essay were presented to the Linnaean Society of London.
“Evolution” scarcely used in The Origin of Species
• “descent with modification”
Ideas behind most Darwin’s most famous book were:
• the unity of life
• the diversity of life
• striking ways in which organisms are suited for life in their environment
Origin of Species
Darwin developed two main ideas
- Decent with modification explains life’s unit its and diversity
- Natural selection is a cause of adaptive evolution
Artificial selection, Natural selection, and adaption
Darwin argued that a process similar to the artificial selection occurs in nature.
Darwin based his argument on two observations, from which he drew two inferences.
Observation #1:
Members of a population often vary greatly in their inherited traits.
• Example: variation in a population.
• Individuals vary in colors and shell
patterns
Observation #2:
All species are capable of producing more offspring than the environment can support. Many of these offspring fail to survive and reproduce.
• Concept of overproduction of the offspring.
• A single puffball fungus can produce billions of spores that give rise to offspring.
• If all of these offspring and their descendants survived to maturity, they would carpet the surrounding land surface.
Environmental resources are limite
Artificial selection, Natural selection, and adaption 2
Inference #1:
Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.
Inference #2:
This unequal ability of individuals to survive and reproduce will lead to the accumulation of favourable traits in the population over generations
Natural selection
Individuals with certain heritable characteristics survive and
reproduce at a higher rate than other individuals.
• Natural selection increases the adaptation of organisms to their
environment over time.
• If an environment changes over time, natural selection may
result in adaptation to these new conditions and may give rise
to new species.
• Although natural selection occurs through interactions
between individual organisms and their environment,
individuals do not evolve
It is the population that evolves over time
• Natural selection can amplify or diminish only those heritable traits that differ among
the individuals in a population.
• Environmental factors vary from place to place and over time.
• A trait that is favorable in one place or time may be useless in other places or
times.
• Natural selection is always operating, but which traits are favored depends on the
context in which a species lives and mates
Natural selection 2
Natural selection does not create new traits, but edits or selects for traits already present in the population.
The local environment determines which traits will be selected for or selected against in any specific population
Natural Selection: A Summary
• Survival of the Fittest: Individuals with certain heritable adaptive characteristics survive and reproduce at a higher rate than other individuals.
• Natural selection increases the adaptation of organisms to their environment over time.
• Speciation: If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species
The Evolution of Drug Resistant Bacteria
• An example of ongoing natural selection that
dramatically affects humans is the evolution of drug-resistant pathogens.
• This is a particular problem with bacteria and viruses because they can produce new generations in a short period of time.
• As a result, resistant strains of these pathogens can proliferate very quickly.
• An example can be represented by the Staphylococcus aureus.
• The story begins in 1943, when penicillin became the first widely used antibiotic.
• By 1945, more than 20% of the S. aureus strains seen in hospitals were already resistant to penicillin.
• These bacteria had an enzymes, penicillinase, that could destroy penicillin.
• S. aureus is an example taken to highlight three key points about natural selection:
✓ natural selection is a process of editing, not a creative mechanism
✓ in species that produce new generations in short periods of time, evolution by
natural selection can occur rapidly, in just a few years or decades
✓ natural selection depends on time and place
Convergent Evolution
Evolution of similar, or analogous, feature in distantly related groups. Analogous traits arise when groups independently adapt to similar environments in similar ways.
Homology
A second type of evidence comes from analysing similarities among different organisms
Evolution is a process of decent with modification
Characteristics present is an ancestral orgmainsim are altered (by natural selection) in its descendants over time as they face different environmental conditions.
Related species can have different characteristics that have underlying similarity yet function differently
Homology is similarity resulting from common ancestry.
Homologies and «Tree Thinking»
• Biologists often represent the pattern of descent from common ancestors with an evolutionary tree
• a diagram that reflects evolutionary relationships among groups of organisms
• The picture shows an evolutionary tree of tetrapods and their closest living relatives, the lungfishes
• Each branch point represents the most recent common ancestor of the two lineages diverging from that point.
• based on anatomical and DNA sequence data
• Tetrapod limbs: limbs with digits
• Amnion: protective embryonic membrane
• Feathers
The fossil record
• A third type of evidence for evolution comes from fossils.
• The fossil record provides evidence of:
• Extinction of species
• Origin of new groups
• Changes within groups
• past organisms differed from
present-day organisms
Biography
• A fourth type of evidence for evolution
comes from biogeography, the geographic
distribution of species.
• The geographical distribution of
organisms is influenced by many factors
including continental drift
Continental Drift; slow movement of the earths continents over time
Evolution of populations
Genetic variation makes evolution possible.
• Individuals within all species vary in their phenotypic traits.
• Phenotypic variations often reflect genetic variation
• differences among individuals in the composition of their genes or other DNA sequences
• Variation in individual genotypes in the nucleotide sequence of DNA
Mutations are changes in the nucleotide sequence of DNA. Not all phenotypic variation is heritable
Evolution of population 2
➢ Only mutations in cells that produce gametes can be passed to offspring
➢ In Genetics we studied that a mutation represents something negative due to the
absence or alteration of the corresponding protein.
➢ In Evolution the mutation does not mean something negative.
➢ On the contrary, the mutation might represent that trait that gives the offspring
an advantage for example in escaping predators, obtaining food, or tolerating
physical conditions
