Pearson Baccalaureate Biology Standard Level 2nd Edition Print and Ebook Bundle for the IB Diploma
Complete summaries and study guides on the chapters of Pearson Baccalaureate's Biology Standard Level IB book. Detailed summaries of up to 10 pages with illustrations. These documents helped me get a good 6 in the IB exams of May 2019 :)
--> This document is on Chapter 5: Evolution
Evolution
the process of cumulative change in the heritable characteristics of a population.
Over time, if enough changes occur in a population, a new species might form whose members will be so
different from the pre-existing population that they no longer will be able to interbreed. = speciation
Charles Darwin started on a scientific exploration in 1831 → idea of evolution by natural selection
Evidence for evolution by natural selection
The fossil record Animal breeding = artificial Homologous
selection structures
…is the accumulation of evidence After practising selective breeding → Evidence that some
from skeletons and footprints etc. By for hundreds of years, we’ve actually very different
looking at the ratio of radioactive realized that some animals now organism have a
14C to stable 14N, we can determine have unique combinations of common ancestor (e.g.
the age of a fossil (half lives).* characteristics that did not exist pentadactyl limbs)
- no transitional forms in the fossil before.
record supporting Darwin’s Humans’ choice; doesn’t work like
argument that a species’ genetic this in natural ecosystems.
characteristics change gradually
before forming a new species.
* Ageing fossils: Age of rock can be determined by examining differences in the ratios of isotopes
(versions of atoms, different mass). As the radioactive carbon 14C loses its radioactivity with time it
transforms into another atom, 14N. → parent isotope into stable daughter isotope = radioactive decay.
The speed in which this decay happens can be expressed as an isotope’s half-life.
= looking at the ratio of 14C to 14N (and knowing the half-life) one can determine the age of
fossils.
+ later DNA evidence = contradicted in some ways Radiometric dating of fossils:
Darwin’s theory of natural selection + Mendel’s work confirmed by later understanding of DNA/
genetics = Neo-Darwinism (evolutionist theory as it exists today)
Examining differences in the ratios of isotopes (= heavier or lighter versions of atoms). Carbon
-14 which is also present in rock and fossils is radioactive and slowly loses its radioactivity with time and
transforms into another atom, nitrogen -14. This transformation of a radioactive parent isotope into a
stable daughter isotope is called decay, which is expressed as an isotope’s half-life (=time it takes for half
of the parent isotope to decay into a stable daughter isotope). The half-life of carbon -14 is 5730 years and
by looking at the amount of the radioactive isotope, we can calculate the age of fossils etc.
Adaptive radiation:
occurs when many similar but distinct species evolve relatively rapidly from a single species. It happens
when certain members of the population exploit a slightly different niche in an ecosystem in a more
successful way. A new species evolves by natural selection and the presence of some barrier. (e.g.
Darwin’s finches) The bigger the geographical distribution, the more differences in the DNA within a
species. → individuals adapt to soil, climate etc. and only the ones best adapted survive and reproduce =
selective pressure.
→ Continuous variation and the concept of gradual divergence: Concept of adaptive
radiation/selective pressure continues to produce genetic differences over a long enough time. →
emergence of two different species = no reproduction
Transient polymorphism = temporary changes in the form a species:
Peppered moths come in two form. The peppered form (99%) and the melanic or black form (1%).
During the industrial revolution, the air was filled with black soot causing the trees to turn rather black.
Normally the melanic form quite struggles to camouflage itself against the white trees which is why this
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