Change Through Time: Theories and Evidences of Evolution

Scientists speculated that organisms change over time. The British naturalist Charles Darwin made the most important contribution to scientific knowledge in 1859 on how organisms change or evolve over time. Darwin explained that the environment selects the kinds of adaptations in organisms that will help them to survive.

(Charles Darwin)

Scientist believed that this change affected a group of organisms called species.

Theories of Evolution

Darwin was not the first to propose a theory explaining the variety of life on earth. One of the most widely accepted theories of evolution during Darwin's time was that proposed by Jean-Baptiste de Lamarck.

(Jean-Baptiste de Lamarck)

Lamarck's Theory

In 1809, Jean-Baptiste de Lamarck, a French biologist, presented his work Zoological Philosophy to explain the origin of species.

(Zoological Philosophy)

His theory proposed the following ideas like

1.) Acquired traits are inherited and passed on to offspring

2.) Organisms possess sertain traits because they constantly use them. This is referred to as "law to use and disuse" or as we might say it now, "use it or lose it."

Lamarck's Hypothesis

• Ancestral giraffes probably had short necks subjected to frequent stretching to reach leaves of trees.
• The offspring had longer necks that were also subjected to frequent stretching.
• The continued stretching eventually produced the modern long necked giraffes.

Darwin Theory

As mentioned earlier Charles Darwin, a British naturalists, published his masterful book the Origin of Species in 1859. In this work, he demonstrated that all living things on earth evolved from other living things. Based on his observations and studies during his voyage of exploration around the world aboard H.M.S Beagle, he developed the Theory of Natural Selection.

(Origin of Species)

His ideas became the foundation of modern evolutionary thought.

1.) Each species produces more offspring than can survive.

2.) These offspring compete with one another for the limited resources available to them.

3.) Organisms in every population differ from one another.

4.) The offspring with the most favorable traits or variations are the most likely to survive and therefore produce more offspring.

Darwin's Hypothesis

• Ancestral giraffes probably had necks that varied in length that each inherited from their parents.
• Natural selection led to survival of the long necked giraffes.
• Finally, only the long necked giraffes survived.

Evidences of Evolution

We know that Lamarck's theory was wrong. Acquired changes that is changes at a macro level in somatic body cells, cannot be passed on to germ cells. For example, if you were to lose one of your fingers, your children would not inherit this trait.

But how did Darwin, who lacked the understanding of genetics, that we have today, come to dismiss Lamarck's ideas? What led him to this idea of natural selection?

In essence, nature selects which living things survive and reproduce.

I find support for the theory of evolution in the following areas.

1.) Biogeography is the study of the distribution of flora (plants) and fauna (animals) in the environment. Scientists have found related species in separated regions of the earth. For example, Darwin observed that animals in the Galapagos Island shared similar characteristics with those in the mainland of South America. Scientist say that these animals have similar characteristics because they share common ancestors. There may be other explanations for similar traits but it is pretty safe to say that they share a common ancestor.

(Biogeography)

2.) Paleontology or the study of fossils. Paleontology has revealed to us the great variety of organisms and the major lines of evolution.

(Paleontology)

3.) Embryology or the study of the development of an organism. If you look at the early stages in vertebrate development, all embryos look alike.

(Embryology)

4.) Comparative Anatomy or the study of physical structures of various animals. Scientists have discovered that some animals have similar structures that perform different functions.

(Comparative Anatomy)

As shown above are all the same appendages but they have evolved to perform different function. These structures called homologous structures also point to a common ancestor.

In contrast some animals have features with the same function but are different in structures. Consider a bat's wing and an insect's wing. Both are used to fly. While they have the same function, they evolved totally differently from one another. These are called analogous structures.

5.) Molecular Biology. Perhaps the most compelling proof of all is the similarity at the molecular level. With the help of technology, scientists can now examine the nucleotide and amino acid sequence of different organisms. These analyses reveal that organisms that are closely related have a greater sequence in common than distantly related species.

For example, we don't look like chimpanzees but studies reveal that approximately 99% of the genetic code is identical to that of a chimpanzee.

Image Source:

0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12

Summarize by @lapilipinas

Reference: 

http://schoolbag.info/biology/ap_biology/79.html

Special Thanks to Google Search and Wikipedia for the references.

Thanks to sir @pfunk helping me, how to quote the sentence or the paragraph from my source and  for the advice  to post the site as reference instead thanking Google and Wikipedia as references......

Please, don't sleep in the class.