Evolution-2 Flashcards
what is paleontological evidence for evolution
(i) Fossils are remains of hard parts of
life-forms found in rocks. Rocks form sediments and a cross-section of
earth’s crust indicates the arrangement of sediments one over the other
during the long history of earth.
ii)Different-aged rock sediments contain
fossils of different life-forms who probably died during the formation of
the particular sediment. Some of them appear similar to modern
organisms (Figure 6.2). They represent extinct organisms (e.g., Dinosaurs).
iii)A study of fossils in different sedimentary layers indicates the geological
period in which they existed. The study showed that life-forms varied
over time and certain life forms are restricted to certain geological timespans. Hence, new forms of life have arisen at different times in the history
of earth. All this is called paleontological evidence.
describe embryological evidence support for evolution
Embryological support for evolution was also proposed by Ernst
Heckel based upon the observation of certain features during embryonic
stage common to all vertebrates that are absent in adult. For example,
the embryos of all vertebrates including human develop a row of vestigial
gill slit just behind the head but it is a functional organ only in fish and
not found in any other adult vertebrates. However, this proposal was
disapproved on careful study performed by Karl Ernst von Baer. He noted
that embryos never pass through the adult stages of other animals.
basis of convergent and divergent evolution
Comparative anatomy and morphology shows similarities and
differences among organisms of today and those that existed years ago. Such similarities can be interpreted to understand whether common
ancestors were shared or not.
what is divergent evolution
For example whales, bats, Cheetah and
human (all mammals) share similarities in the pattern of bones of forelimbs
(Figure 6.3b). Though these forelimbs perform different functions in these
animals, they have similar anatomical structure – all of them have
humerus, radius, ulna, carpals, metacarpals and phalanges in their
forelimbs. Hence, in these animals, the same structure developed along
different directions due to adaptations to different needs. This is divergent
evolution and these structures are homologous.
examples of homolgous structures
-forelimbs of various mammals
- vertebrate hearts, brains
-in plants,
- thorn of bougainvillea and tendril of curubita
what is analogy or convergent evolution
Wings of butterfly and of birds
look alike. They are not anatomically
similar structures though they perform
similar functions. Hence, analogous
structures are a result of convergent
evolution - different structures evolving
for the same function and hence having
similarity. Other examples of analogy are
the eye of the octopus and of mammals
or the flippers of Penguins and Dolphins.
One can say that it is the similar habitat
that has resulted in selection of similar
adaptive features in different groups of
organisms but toward the same function:
Sweet potato (root modification) and
potato (stem modification) is another
example for analogy.
what could be the biochemical reason behind the similarity in all organisms
similarities in proteins and genes
performing a given function among diverse
organisms give clues to common ancestry.
These biochemical similarities point to the
same shared ancestry as structural
similarities among diverse organisms
describe the situation of the white and darkwinged moths in england? how did it change bfr and after industrialisation
In a collection of moths made in 1850s,
i.e., before industrialisation set in, it was observed that there were more
white-winged moths on trees than dark-winged or melanised moths.
However, in the collection carried out from the same area, but after
industrialisation, i.e., in 1920, there were more dark-winged moths in
the same area, i.e., the proportion was reversed.
explanation for melanised moths
‘predators will
spot a moth against a contrasting background’
During postindustrialisation period, the tree trunks became dark due to industrial
smoke and soots. Under this condition the white-winged moth did not
survive due to predators, dark-winged or melanised moth survived. Before
industrialisation set in, thick growth of almost white-coloured lichen
covered the trees - in that background the white winged moth survived
but the dark-coloured moth were picked out by predators. Do you know
that lichens can be used as industrial pollution indicators? They will
not grow in areas that are polluted. Hence, moths that were able to
camouflage themselves, i.e., hide in the background, survived
(Figure 6.4). This understanding is supported by the fact that in areas
where industrialisation did not occur e.g., in rural areas, the count of
melanic moths was low.
conclusion of melanised moths
This showed that in a mixed population, those
that can better-adapt, survive and increase in population size. Remember
that no variant is completely wiped out.
describe instances of evolution by anthropogenic action
(i) Similarly, excess use of herbicides, pesticides, etc., has only resulted in
selection of resistant varieties in a much lesser time scale.
(ii) This is also true for
microbes against which we employ antibiotics or drugs against eukaryotic
organisms/cell. Hence, resistant organisms/cells are appearing in a time
scale of months or years and not centuries.
(iii)Man has bred selected plants and
animals for agriculture, horticulture, sport
or security. Man has domesticated many
wild animals and crops. This intensive
breeding programme has created breeds
that differ from other breeds (e.g., dogs) but
still are of the same group.
These are examples of evolution
by anthropogenic action.
what is evolution to nature
This also tells us that evolution is not a directed
process in the sense of determinism. It is a stochastic process based on
chance events in nature and chance mutation in the organisms.
