Evolution by Natural Selection Flashcards
What is a Hypothesis?
Hypotheses: a possible explanation for an observation
What is a Theory?
Theory: an explanation for something that has been
observed in nature which can be supported by facts,
generalizations, tested hypotheses, models and laws.
What is the theory of evolution / theory of “descent with
modification”?
Theory of evolution: all things that we see today arose
from things that existed in the past but they look different because things change over long periods of time.
What is biological evolution?
changes in living things over long periods of time.
Definition of species
group of similar organisms that are able to
interbreed and produce fertile offspring.
Definition of population
the sum of organisms of the same species
occupying the same habitat at the same time and having the ability to interbreed.
Definition of variation
small differences that exist between individuals of
the same species or population.
What is a mutation?
change the structure of a gene → altered
genotype → altered phenotype
Sources of variation - small differences that exist between individuals of the same species or population.
- Mutations: change the structure of a gene → altered
genotype → altered phenotype - Variation due to meiosis:
- Crossing over: during P1, the homologous chromosomes swap a segment of DNA.
- Random arrangement of chromosomes: during M1 and M2. Chromosomes arrange randomly at the equator of the cell. - Random fertilization of gametes: egg and sperm cells produced by meiosis are all different so random
fertilization results in different combinations of genetic
material in offspring.
Types of variation: continuous variation
There are a range of different phenotypes for a particular characteristics. E.g. height
- Brought about by many genes working together (polygenic inheritance)
- Environment can affect the appearance of characteristics.
- When plotted on a bar graph – you see a bell-shaped, normal distribution curve is produced.
Types of variation: discontinuous variation
There is no range of different phenotypes for a particular characteristic.
- The characteristic is either present or not. E.g. blood groups (you can either be one blood group or another, there is no in-between phenotype).
- Usually controlled by alleles of a single gene.
- Environment has little effect on this type of variation.
Who created the theory Lamarckism?
Jean-Baptiste Lamarck
What are the 2 main ideas/laws of Lamarck – theory of transformation:
- Law of use and disuse: organs are modified or adapted according to how frequently they are used. If they are used more frequently, they become larger and if an organ is disused, it became smaller
until it totally disappeared. - Law of inheritance of modified or acquired characteristics: the modifications brought about by the use or disuse were able to be transmitted to their offspring.
Rejection of Lamarck’s theories
- Organisms can’t choose to evolve, changes take place randomly.
- There is little evidence to support the idea that changes brought about by adaptation to the environment are inherited from parent to offspring.
Who created the theory of evolution by natural selection, Darwinism?
Charles Darwin
What observations and assumptions is Darwinism based on?
- Variation: there is variation in appearance and abilities of organisms within every species.
- Offspring: species produce a large number of offspring but they don’t all survive.
- Competition: organisms compete for limited resources.
- Genetics: Organisms pass their genes on to their offspring.
- Natural Selection: Organisms with the most beneficial traits are more likely to survive and reproduce.
Why is Darwin’s theory referred to as phyletic
gradualism/gradualism sometimes?
because evolution occurs gradually and uniformly over long periods of time.
What is punctuated equilibrium?
organisms don’t undergo any changes for a long period of time (stasis). Then, suddenly, the species undergo a rapid change over a short period of geological time → a new species.
Could rapid change occur over short periods of time?
YES – when natural selection is strong, rapid
and substantial evolutionary changes can occur.
What is natural selection?
the process whereby organisms better adapted to their environment tend to survive and produce more offspring.
Why would species experience long periods of stasis
without changing?
Stasis is possible when environment does not
change or when changes in the environment oscillate
back and forth. When species shift their geographical
ranges, stasis is also possible.
Definition of Speciation?
formation of a new species
Types of Speciation
- Allopatric speciation
2. Sympatric speciation
- Allopatric speciation (speciation by geographical isolation)
⚫ When a population becomes separated into 2
sub-populations by a geographic barrier (isolation such
as a mountain or river). Each sub-population develops
into a new species.
⚫ The 2 populations become genotypically and
phenotypically different from each other. These
differences may prevent interbreeding even if they mix.
⚫ One or both populations may become a new species.
