How the works of Charles Darwin and Gregor Mendel contribute enormously to our understanding of the heritability of characteristics

I. Content

1. Introduction

2. Darwin and his work
2.1 Short biography
2.2 Theories

3. Mendel andhis work
3.1 Short biography
3.2 Theories

4. Conclusion
4.1 Summary
4.2 Back to the research question
4.3 Limits

II. Bibliographical References

1. Introduction:

Charles Darwin (1809 - 1882)¹ was the first person who explained an evolutionary theorie and the transmutations ofspecies by natural selection and fitness. He stated that character traits are passing from one generation to another. But he didn’t explain how this took place.

This is where Gregor Mendel (1822-1884)² appears on the scene. He conducted research with pea plants and made genetical experiments. He was one of the major pioner handling with genetics. In the main Mendel figured out that two different types of genes do exist.

I will go more into deep under the chapters 2.2 and 3.2 ‘Theories’.

In the following these themes about genetics and how we -humans and every creature on this earth- are receiving our characteristics, is what I want to single out during this essay.

2. Darwin and his work:

2.1 Short Biography:

Abbildung in dieser Leseprobe nicht enthalten

The most important fact about Darwin’s life for its studies and which can’t be seen in this chart is:

“Darwin's belief in the special creation of species, with which he began the voyage, was shaken by the vast array of species and adaptions the voyage introduced to him. The issue would come especially into focus on the Galapagos Islands, off the west coast of South America. Each island contained its own assortment of species, some found only on that particular island. Local experts could tell at sight from which of the several islands a particular tortoise came. The same was true of many of the bird and plant species Darwin collected.

What all of this implied came gradually to Darwin after his return.”^{3 4}

2.2. Theories:

The first thing coming in my mind, when hearing about the combination of evolutionary theory and Darwin is ‘the fittest survives’. Of course it is not possible to reduce Darwin on this simple phrase. For Mayr⁵ there are five hypotheses belonging to the work ‘On the Origin of Species’ by Darwin:

(1) Naturalism (or materialism): Questions about the origins of species are explained by natural processes and the laws governing them.
(2) Transmutation: Species (and other taxa) are not fixed types.
(3) (Monophyletic) descent with modification: All phylogenetic branching goes back to a common ancestor.
(4) Natural selection: Transmutation and descent with modification reflect differences in reproductive rates caused by differences in relative adaptedness of chance variants to a given environment.
(5) Causal pluralism: Natural selection is the dominant, but not the only, cause of evolution. Subordinate causes include the inheritance of acquired characteristics and sexual selection.

Just to make this complex topic a little bit easier, I want to single out two terminologies, which are for me the most important ones, to comprehend Darwin: natural selection and fitness.

Natural selection is:

“[...] the idea, that traits which are adaptive, leading to increased survival and reproductive potential, are likely to become more prevalent in the species over generations.”⁶

And by ‘Fitness’ the definition is meant:

“[...] the extent to which one's characteristics promote longevity and reproductive potential.

Therefore, those genes which confer fitness are more likely to survive natural selection.

Fitness involves both survival and reproduction.”⁷

But all in all, how did Darwin made these conclusions? We know from the biography, that his most impressing experience took place on the Galapagos Island. He compared this place with the Cape Verde Island (Africa), which had the similar climate and soil (volcanic nature) and also the islands had same height and size. But they did not have the same inhabitants - why?⁸

“For Darwin, the issue came down to this,

Why should the species which are supposed to have been created in the Galapagos Archipelago, and nowhere else, bear so plainly the stamp of affinity to those created in

[South] Africa?”⁹

Darwin had just two possible answers: either they were products of aspecial creation or they were the natural results ofevolutionary adaption to the different islands.¹⁰ He came to the conclusion, that:

“If acts ofspecial divine Creation, then each ofthe many hundreds ofthe island species represented a distinct and separate act of creation. But that seemed odd. All were similar to each other-the tortoises, to other tortoises, the birds to other birds, and the plants to other plants on the various islands, almost as if the Creator was running out of new ideas. On the other hand, if they were the natural results of common evolutionary descent, then similarity and diversity might be expected. For example, the tortoise species on different islands illustrated adaption to distinct environments. The similarities they shared were explained by descent to the present traced from a common ancestor from the past. The first animals or plants washed or blown to these oceanic islands would constitute the common stock from which similar, but eventually distinct, species evolved. Darwin sided with a natural evolution.”¹¹

So taking everything in conclusion, we can state, that both adaption and natural evolution leave an imprint on the characteristics of living organism. But how does hereditiy get along? How does it biologically function? How do parent’s bequest their genes to their children?

To get the answers, we have to switch to Gregor Mendel.

“When Charles Darwin published his ideas on evolution and heredity in 1868, he was completely unaware of the mechanisms by which the instructions for the development of each organism are passed down from generation to generation. However, two years previously,

Gregor Mendel, an Austrian monk, published an account of his breeding experiments with pea plants. Within this work lay the answers to Darwin's problems. Mendelian theory was to become an essential basis for the study of genetics.”¹²

[...]

¹ http://en.wikipedia.org/wiki/Charles_Darwin

² http://en.wikipedia.org/wiki/Gregor_mendel

³ http://darwin-online.org.uk/timeline.html

⁴ Kardong (2008): p.10.

⁵ Mayr in Depewand Weber(1997): p.169.

⁶ AP1123 (UCC; Dr. Mike Murphy): Lecture2-Evolution. 14|01|2011

⁷ AP1123 (UCC; Dr. Mike Murphy): Lecture2-Evolution. 14|01|2011

⁸ Kardong (2008): p.11f.

⁹ Kardong (2008): p.12.

¹⁰ Kardong (2008): p.12.

¹¹ Kardong (2008): p.12.

¹² http://www.fathom.com/feature/122612/index.html