BS1070 Notes
Evolution and Natural Selection
Charles Darwin is the primary focus of this area. It started in the 1800s when biologists
began thinking of the diversity of life. There were others at the time who proposed ideas
about populations though. Malthus and Mendal were both in this era too.
The study of fossils was key in Darwin's ideas
George Cuvier was key as well in pioneering palaeontology.
Lamarck’s hypothesis of evolution
French biologist Jean-Baptiste de Lamarck hypothesized that species evolve through use and
disuse of body parts and the inheritance of acquired characteristics. The mechanisms he
proposed are unsupported by evidence
Darwin journeyed on the HMS Beagle all over but on the Galapogos he found the birds had
different beaks depending on what they consumed.
In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with
modification, but did not introduce his theory publicly
Natural selection is a process in which individuals with favourable inherited traits are more
likely to survive and reproduce
In June 1858, Darwin received a manuscript from Alfred Russel Wallace, who had developed
a theory of natural selection similar to Darwin’s
Darwin quickly finished The Origin of Species and published it the next year
Darwin never used the word evolution in the first edition of The Origin of Species
There is also artificial selection which is brought about by humans
Two important points about organisms
Observation #1: Members of a population often vary in their inherited traits
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
Observation #2: All species can produce more offspring than the environment can support,
and many of these offspring fail to survive and reproduce Inference
#2: This unequal ability of individuals to survive and reproduce will lead to the accumulation
of favourable traits in the population over generations
There are several key points about natural selection
Key points of natural selection
,• Individuals with certain heritable traits survive and reproduce at a higher rate than other
individuals
• Natural selection increases the frequency of adaptations that are favourable in a given
environment
Further evidence has emerged for evolution. This can be seen in the emergence of antibiotic
resitant bacteria. MRSA is probably the most well known example of this.
Homology
This is the similarity that comes from common ancestry. Homologous structures are
anatomical resemblances that represent variations on a structural theme present in a
common ancestor. This can be seen in the structure of mammal limbs for example.
Homology is useful in the construction of evolutionary trees.
Convergent evolution
Convergent evolution is the evolution of similar, or analogous, features in distantly related
groups
Biogeography, the scientific study of the geographic distribution of species, provides
evidence of evolution
Earth’s continents were formerly united in a single large continent called Pangaea, but have
since separated by continental drift.
Species and Speciation
The biological species concept emphasizes reproductive isolation.
• Species is a Latin word meaning “kind” or “appearance”
• Biologists compare morphology, physiology, biochemistry, and DNA sequences when
grouping organisms
Reproductive isolation is the existence of biological factors (barriers) that impede two
species from producing viable, fertile offspring. Hybrids can be present though. They are
often infertile though.
There are various barriers that prevent the formation of these creatures though.
, There are limitations of the species model though.
The definition of barrier depends on the ability of a population to disperse –For example, a
canyon may create a barrier for small rodents, but not birds, coyotes, or pollen
Separated populations may evolve independently through mutation, natural selection, and
genetic drift
Reproductive isolation may arise as a by-product of genetic divergence
There is also sympatric speciation that is used too. In sympatric speciation, speciation occurs
in populations that live in the same geographic area
Sympatric speciation can occur if gene flow is reduced by factors including –Polyploidy –
Sexual selection–Habitat differentiation
Hybrid zones reveal factors that cause reproductive isolation
These are border like areas that can be found where species will mate with each other.
Speciation can occur rapidly or slowly and can result from changes in few or many genes
• Many questions remain concerning how long it takes for new species to form and how
many genes need to differ between species
• The rate of speciation can be studied using the fossil record, morphological data, or
molecular data
• The interval between speciation events can range from 4,000 years (some cichlids) to 40
million years (some beetles), with an average of 6.5 million years
Introduction to Adaptation
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