Heredity and Evolution

Evolution

We have heard this particular statement that we have evolved from our ancestors. What is seen now on planet earth is a result of evolution. So, what exactly is evolution? Is there any science behind it? Come let us find out interesting facts about evolution and speciation.

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The Basic Idea of Evolution

There is a lot of science behind the theory of evolution. Scientists and researchers have done intensive studies to show how living things evolved and how traits and characteristics passed on from generations to generations.

Ultimately, when we speak of evolution, we actually speak of the genetic characteristics that are inherited and passed on from one generation to the other. The whole process of evolution gives rise to biodiversity at all levels, including species, organisms, and even molecules.

An important basis on which the theory of evolution is based on is that all species are related and gradually change over time. But the frequency of an inherited trait that undergoes a change is spread over generations. Genes control the traits. Therefore we can say that the frequency of genes in a population changes over generations.

Acquired and Inherited Traits

Acquired traits are qualities that are developed in an individual in response to certain conditions in the environment. These cannot be transferred to the progeny. They only help an organism to survive. And therefore, they do not direct the evolution process.  Examples include bending of plants due to wind, calluses (Corns or even hard skin) on fingers etc.

Inherited traits are the characters or qualities that are passed on from parents to their offspring i.e. from one generation to the other generation. They have a major role in the evolution process. Some examples include the color hair, eyes, shape of the nose, bone structure etc.

Speciation

Speciation

( Source – Encyclopedia Brittanica)

The formation of new species from the existing species is called as speciation. Here, a single evolutionary lineage splits up into two or more genetically independent lineages. The occurrence of speciation is due to the following reasons:

  • Genetic drift – A random change in the frequency of alleles over successive generations in a population.
  • Gene flow – This speciation occurs between populations which are partly separated but not completely separated.
  • Natural selection – Nature selects and consolidates those organisms which are more suitable and adaptable. They also possess favourable variations.
  • Geographical isolation – This is caused by mountains, rivers, and other geographic features. This form of isolation leads to reproductive isolation. As a result, there is no flow of genes in the separated groups of the population.

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Evolution

Evolution and Classification

So, how does evolution play a role in classifying organisms?  In your previous classes, you have learned how living organisms are classified into various groups and subgroups. The basis of classification is the closeness of the species in each group. Each subgroup of species has a recent common ancestor which again has a distant common ancestor. And, so as you go backward, you will then trace back to the very beginning of life on earth, where all organisms have evolved from a common ancestor. Thus you can see how classification and evolution are interlinked.

Species are classified based on their evolutionary relationships. When species have common characteristics, they are closely related. The more closely they are related, the more likely is the chance of a common ancestor. Similarities between organisms thus allow us to classify them together.

Tracing Evolutionary Changes

speciation and evolution

(Source: DiffernceBetween.com)

When we trace the changes that have evolved over a period of time, we notice that there is a common ancestor. When we trace these evolutionary changes, we can conclude the evidence of evolution through the following:

Homologous evidence – The homologous organs seen in organisms show us they have a common ancestor.  For example, when you look at the forelimbs of whales, humans, birds, and dogs, the bone structure is similar, but they look different on the outside.

Analogous evidence – Some physical features in organisms may look alike. But these have no common ancestor. These traits have evolved independently. The basic structure of the organs is different, but they perform similar functions.

Fossils (Paleontological evidence) – These are the preserved remains of organisms that lived in the past. These fossils also help us trace back the evolution process.

Stages of Evolution

When you see the evidence of evolution, you can come to a conclusion that the stages of evolution have occurred bit by bit, over many generations. An example could be the emergence of feathers, which may have started as a means to provide insulation in cold weather. Slowly, this must have improvised to help in the ability to fly.

The artificial selection also has a role to play in the evolutionary stages. Humans have successfully used this concept, in developing certain varieties of food crops and vegetables, to suit their needs. For example, the different varieties of broccoli, cauliflower, red cabbage, kale etc. have been developed through the artificial selection process.  The common ancestor here is the wild cabbage!

Human Evolution

When we speak about evolution, I am sure, as science students, you all would love to know about human evolution. Even the evolution of humans has been traced using the same evidence such as the fossils, DNA sequencing, time dating, excavating etc. According to established theories, all human beings evolved in the continent of Africa. And therefore all humans are a single species, Homo sapiens.

(Source – Encyclopedia Britannica)

Solved Question For You

Q: Differentiate between homologous organs and analogous organs with examples.

Ans. Homologous organs are the organs that have a same structural design but different function. Eg. The forelimbs of whales, humans, birds, and dogs have the same bone structure. But each performs functions according to the habitat that the animals live in.

Analogous organs are the organs that perform similar functions but have the basic structural design is different. Eg. The wings of a bat and a fly are analogous organs.

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