The infinite variety: the beginning of life



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THE INFINITE VARIETY: THE BEGINNING OF LIFE

Foreword




This material was originally prepared for a first year tutorial system at the Zoology Department and is built around the David Attenborough film series “Life on Earth”. At the time of development there was no intention to develop it as eLearning content. With the introduction of the Ecological Informatics courses at the University of the Western Cape, it became necessary to provide a basic review of how Biodiversity evolved? In updating extensive use of hypertext is used so you can dip and out at various points of the material and get additional information. This material should be used in conjunction with viewing of the material “Life on Earth” by David Attenborough, but we also encourage you to follow the hyperlinks and examine the classifications provided.
It should be realized that science and especially our understanding of how biodiversity evolved is continuously changing – so we have had to correct certain information and provide text boxes with the latest information and access to recent scientific papers.






For both updating and providing supplementary information I have used the public domain Wikipedia Encyclopaedia, and unless otherwise stated all images and nomenclature/classifications were sourced from Wikipedia and Wikispecies.




At the end of each chapter are some self-study questions plus the link to the really excellent Public Broadcasting Service (PBS) “Shape of Life” series which is available for viewing from the following url:

http://www.pbs.org/kcet/shapeoflife/episodes/index.html. It is very important that this material is reviewed in combination with this online course and in the absence of access to the “Life on Earth” is a good substitute.

This resource was developed using standard html and ccs and should work under all platforms and browser configurations, but extensive use of pop-up is made which means that you must enable pop-ups and your browser is java-enabled.


For registered UWC students assessment criteria will be provided separately through continuous assessment (using electronic quizzes), discussion forum and a course-project.
Good Luck with your Biodiversity studies.


Richard Knight


Coordinator: National Information Society Learnership- Ecological Informatics

c/o Department of Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17

Bellville 7535

South Africa


Phone: 27 + 21 + 959 3940

Email: rknight@uwc.ac.za




Darwin and the Giant Tortoises
The world is rich in animals and plants, some of which still remain to be discovered. A small area of the Tropical Forests of South America will still yield insects that have never been described, the difficulty is finding a specialist whose is able to classify them. The understanding of such biodiversity would have been almost impossible, if it had not been for Charles Darwin and his trip around the world. For example Darwin described the adaptations of the Giant Tortoises (Geochelone nigra) that occur on the Galapagos Islands in the South Pacific.
Tortoises occurring on the well-watered islands, with short, cropped vegetation had gently curved front edges to their shell.

An example of dome-shell Galapagos Tortoise that occurs on the well-watered parts of the islands.
Tortoises occurring on more arid islands had to stretch their necks to reach branches of cactus and other vegetation. Consequently, these later individuals had longer necks and a high peak to the front edges of their shells, which enabled them to stretch their heads almost vertically.

A “saddle-back” Galapagos Tortoise that inhabits drier areas of the islands and has a longer neck and a high peak to the front edge of its shell, this enables it to stretch it neck further out and obtain food higher up off the ground.
Observations such as these were the foundations for the theory of evolution, which suggests that species were not fixed for ever but changed with time and thereby contribute to the immense diversity of life.
Geochelone nigra
Galápagos Tortoise



Scientific classification

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Testudines

Family: Testudinidae

Genus: Geochelone
Binomial name Geochelone nigra (Quoy & Gaimard, 1824)
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Darwin's argument for the evolution of different necks in these tortoises was as follows:- all individuals of the same species are not identical. In a single clutch of eggs there will be some hatchlings, which, because of their genetic constitution, will develop longer necks than others. In times of drought such individuals will be able to reach leaves higher off the ground than their siblings and therefore will survive. The brothers and sisters in the clutch who possessed shorter necks would be unable to stretch and reach food and therefore would starve to death. Since this time natural selection has been debated and tested, refined, quantified and elaborated. Later discoveries about genetics, molecular biology, population dynamics and animal behaviour have developed the theory of natural selection still further. It remains the key to our understanding of the natural world and it enables us to recognize that life has a long and continuous history during which organisms, both plants and animals, have changed, generation by generation, as they colonized all parts of the world.



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