Evolution-3 Flashcards
what observation was made by darwin on galapagos island
Of particular interest, small black birds
later called Darwin’s Finches amazed him. He realised that there were many varieties of finches in the same island. All the varieties, he conjectured,
evolved on the island itself. From the original seed-eating features, many
other forms with altered beaks arose, enabling them to become insectivorous
and vegetarian finches.
what is adaptive radiation
This process of evolution of different
species in a given geographical area starting from a point and literally
radiating to other areas of geography (habitats) is called adaptive radiation
australian marsupial radiation
Darwin’s finches represent one of the best examples of this phenomenon.
Another example is Australian marsupials. A number of marsupials, each
different from the other (Figure 6.6) evolved from an ancestral stock, but all
within the Australian island continent.
eg: kangaroo, koala, bandicoot, wombat, tiger cat
give an example of convergent evolution and adaptive radiation
When more than one adaptive radiation
appeared to have occurred in an isolated geographical area (representingdifferent habitats), one can call this convergent
evolution.
Placental mammals in Australia also
exhibit adaptive radiation in evolving into
varieties of such placental mammals each of
which appears to be ‘similar’ to a corresponding
marsupial (e.g., Placental wolf and Tasmanian
wolf-marsupial)
mole and marsupial mole
anteater and numbat
lemur and spotted cuscus
flying squirrel and flying phalanger
lamarckism
First theory of evolution by Lamarck (1744-1829).
* Evolution of life forms had occurred but driven by use and disuse of organs.
- Example-
- Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of
their necks. - As they passed on this acquired character of elongated neck to succeeding
generations, - Giraffes, slowly over the years, came to acquire long necks.
- Nobody believes this conjecture any more.
Is evolution a process or the result of a process? T
The world we see,
inanimate and animate, is only the success stories of evolution. When we
describe the story of this world we describe evolution as a process. On the
other hand when we describe the story of life on earth, we treat evolution
as a consequence of a process called natural selection. We are still not
very clear whether to regard evolution and natural selection as processes
or end result of unknown processes.
work of darwin
- Darwin traveled by H.M.S. Beagle.
- The ship left on Dec. 27, 1831 and returned on Oct. 2, 1836.
- He travelled South America, South Africa, Australia and Galapagos Islands.
- Darwin was influenced by two books.
- “Principles of population” of Thomas Malthus.
- “Principles of Geology” of Charles Lyell.
Basic concept of Darwinism-
- Branching descent
- Natural selection
The main features of theory of Natural Selection -1
Over production : (High rate of Reproduction) All organisms have capability to
produce enormous number of offspring.
- Limited carrying capacity of environment : Due to limited space & food.
- Struggle for existence : Every individual competes with other of the same and other
species for basic necessities like space, shelter and food.
The novelty and brilliant
insight of Darwin
he asserted that variations, which are heritable
and which make resource utilisation better for few (adapted to habitat
better) will enable only those to reproduce and leave more progeny. Hence
for a period of time, over many generations, survivors will leave more
progeny and there would be a change in population characteristic and
hence new forms appear to arise.
The main features of theory of Natural Selection- Variations and heredity :
- Micro variations- small, directional & continuous (crossing over & genetic
recombination) - Macro variations- large, non directional & discontinuous (mutations) Not
considered by Darwin. - Two types of mutation-
* Useful and adaptive variations
* Harmful and non adaptive variations
Survival of the fittest or natural selection :
a) The original idea of survival of fittest was proposed by Herbert Spencer.
b) In the struggle for existence only those members survive which posses useful
variations means nature selects fit individuals. This was called Natural Selection. Nature selects for fitness.
c) some organisms are better
adapted to survive in an otherwise hostile environment. Adaptive ability is
inherited. It has a genetic basis.
d)Fitness is the end result of the ability to adapt and get selected by nature.
e) Fitness according to Darwin Reproductive fitness.
Origin of New Species :
a) Variations appearing due to environmental changes are transmitted to the next
generation.
b) So offspring become different from ancestors.
c) In next generation process of Natural selection repeats so after many generation a
new species is formed.
Mutation theory by Hugo de Vries
Hugo deVries based on his work on evening primrose brought forth the idea of mutations – large difference arising suddenly in
a population.
He believed that it is mutation which causes evolution and not the minor variations (heritable) that Darwin talked about.
Mutations are random and directionless while Darwinian variations are small and
directional.
Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step
large mutation).
