- A Trait of an organism which is not inherited but develops in response to the environment is called acquired trait
- Example- When a women eats a lot of food ,She becomes fat and gains weight.
- This is an Acquired Trait.
- Inherited Traits – Only those traits which can be transmitted to future generation in which changes have occurred in the Genes (DNA) present in the reproductive cells of the parent organisms.
A Small Example To Show Variation
- Consider a group of twelve red beetles.
- They live, let us assume, in some bushes with green leaves.
- Their population will grow by sexual reproduction, and therefore, can generate variations.
- Let us imagine also that crows eat these beetles. The more beetles the crows eat, the fewer
beetles are available to reproduce
- Now Imagine there is some variation comes in the color of the Beetle due to reproduction
- In place of red ,Green Coloured Beetle is produced
- and that green colour is transferred to Progeny
- Because of the Green colour of the beetle, Crows cannot find them easily because of same colour of green leaves and Beetle.
- Now Numbers of Green Beetle Increases.and it gave a survival advantage
- In Conclusion the process of natural selection in which the characteristics that help organism to increase its population is passed on
- Genetic drift too causes drastic change in population-Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.
- The Process By which new species develop from the existing species is known as speciation .
The factors affecting Speciation are
- Geographical isolation of a population caused by various types of barriers (such as mountain ranges,
rivers and sea). The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Variations caused in individuals due to natural selection.
- There is an enormous ‘number’ and ‘types’ of living organisms (plants and animals) on this earth.
- Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced
- Pterosaur is an ancient flying reptile which lived on the earth about 150 million years ago
Evidences for Evolution
(i) Homologous organs– Those organs which have same basic structure (or same basic design) but different functions are called homologous Organs .
Example– the forelimbs of a man, a lizard (reptile), a frog (amphibian), a bird and a bat seem to have basic bone design
(ii) Analogous organs- Those organs which have different basic structure (or different basic design) but same functions are called Analogous organs.
Example Wings of Bird and bat
(iii) Fossils-The remains (or impression ) of dead animals or plants that lived in the remote past are known as fossils.
How do we know how old the fossils are?
There are two components to this estimation.
- One is relative. If we dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.
- The second way of dating fossils is by detecting the ratios of different isotopes of the same element in the fossil material.
Evolution by Stages
- Take an example of our eye to understand the process of evolution
- The complex organism like our eye have been created in stages over many generation
- First of all the rudimentary eye like of a roundworm might have formed
- And at later stages the eye would have formed
Sometimes an evolutionary change produced in an organism for one purpose later on becomes entirely different functions .
For example a bird evolved feathers as a means of providing insulation to their bodies in cold weather but later became useful for the purpose of flying .
even dinosaurs had feathers but they could not fly .
The presence of feathers on birds tells us that the birds are closely related to reptiles
Evolution by artificial selection
- Different looking organisms can in fact be created from the same basic design of the ancestor
- Selective breeding /Artificial selection is a technique used when breeding domesticated animals, such as dogs, pigeons or cattle. Some of these animals may have traits that a breeder will want to carry over to the next generation. The breeder will therefore select those animals to breed which have that quality, rather than those that do not.
- Cabbage,Broccoli,Cauliflower ,Kohlrabi and kale might have developed from Wild Cabbage
Evolution Should not be equated with progress
- It will all depend on the environment.
- Also, it is not as if the newly generated species are in any way ‘better’ than the older one.
- It is just that natural selection and genetic drift have together led to the formation of a population that cannot reproduce with the original one.
- So, for example, it is not true that human beings have evolved from chimpanzees.
- Rather, both human beings and chimpanzees have a common ancestor a long time ago
- Excavating, time-dating and studying fossils, as well as determining DNA sequences – have
been used for studying human evolution.
- All humans are a single species
- The earliest members of the human species, Homo sapiens, can be traced from Africa
- Some Ancestors Left Africa while few stayed in Africa
- The migrants slowly spread across the planet – from Africa to West Asia, then to Central Asia, Eurasia,
South Asia, East Asia.
- Like all other species on the planet, they had come into being as an accident of evolution, and were trying to live their lives the best they could.