Tutorial 3: Evolution Flashcards
main concepts within evolution
(1) Organic evolution is a genetic change over time (from generation to generation).
(2) There are four evolutionary forces (i.e. factors that can change gene frequencies).
These are mutation, natural selection, gene flow and random genetic drift.
For now however, we will focus on only one of these forces - natural selection.
(3) Natural selection is dependent upon the environment.
(4) Natural selection is the reason why organisms are said to be adapted to their
environment.
(5) Organic evolution due to natural selection is an inevitable consequence if:
(a) There is inherited variation. This requires:
(i) a system of reproduction,
(ii) genetic material, and
(iii) occasional change in the genetic material (i.e. mutation – which is how
variation arises).
AND
(b) Some inherited differences (variants or forms) have more offspring than
others - i.e. greater reproductive success.
(6) The measure of “reproductive success” is called fitness.
(7) There are multiple bodies of evidence to demonstrate that all living organisms on
this planet have a common ancestry.
In what ways might the peacocks’ tail reduce survival? (There are several aspects to
consider here)
It is large and unwieldy so it requires more energy to drag around.
This energy could be better used for just staying alive.
It is also very visible – so males are potentially more visible to predators and less
able to escape quickly with such a bulky tail.
It is very costly to grow – again using energy that could be used elsewhere.
Note that peacocks shed their tails after the mating season.
In what ways might a peacock’s tail potentially increase that individual’s reproductive
success?
It acts as a sensory cue imparting information about a male’s ’potential’ value as a mate (in terms of the quality of his genes) to peahens who are therefore willing to mate preferentially with the male with the ‘best’ tail. Compared to other males in the population the male with the ‘best’ tail ends up with more partners, which can result in more offspring.
Practice Exam Question: Explain how a peacock’s tail can result in an INCREASE
in fitness even though the survival of the individual may be compromised / adversely
affected.
Fitness consists of survival and fertility. If the increase in fertility (through the ability
to attract multiple mates) outweighs the decrease in survival, then fitness overall is
increased.
Practice Exam Question: Explain how natural selection has acted on the body shapes of indigenous peoples in different climates.
Climate change is a selection pressure
People living in cold climates tend to have large, stout trunks and short thick limbs to reduce heat loss.
People living in hot climates tend to have long thin limbs and small trunks to maximize heat loss.
Those with better suited body shape survive longer and have increased
fitness, therefore trait increases in frequency over time
Comparative anatomy explores and establishes the functional correspondences between body parts of organsis
kom different species that have adapted to different lifestyles (e.p. those between the wings of bats, birds ano
insects) and correspondences of origin (e.g, the wings of flies and mosquitos).
A. While homologous structures show how similar species have changed from their ancient ancestors (divergent
evolution), analogous structures show how different species have evolved to become more similar (convergent
evolution).
B. Species that share a similar appearance sometimes arise because, by leading similar lifestyles, natural selection has
favoured the evolution of similar adaptations. For example, bird and insect wings are similar because they carry out
the same type of function but structurally and embryologically they are very different. These adaptations are referred
to as analogous features.
Homologous structures are the same body parts that are modifled in different ways in different lines of descent from a
common ancestor. Such structures may look quite different and perform different tasks, but they can still be traced
back to a common structure in an animal that was ancestral to both.
D. The physical similarity evident between vertebrates early in embryological development is an example of historical
legacy known as phylogenetic constraint.
Two key features of adaptive radiation are that the descendant species all evolved from a common ancestor and they
are all adapted to occupy different niches.
Continental drift is a major reason as to why we see convergent evolution in the adaptive radiations of marsupials and
nammals.
wrong
Bats, honey gliders, birds and insects represent an adaptive radiation.
Cladogenesis (branching evolution) is the means by which adaptive radiations occur.
A. A living fossil is a modern organism that has changed little from its ancient fossil ancestors.
wrong
For evolution to occur via anagenesis, the environment must remain stable.
C. Anagenesis is the transformation of a single ancestral species into a single descendant species.
D. Archaeopteryx, an organism that shares features with both birds and reptiles, is an example of an intermediate form
representing a group that was very close to a major cladistic event.
