WEIT Chap4

The Geography of Life

==Intro: The distribution of species around the world are surprisingly specific. To understand the distribution of species, we must take in account the movement of continents, for example Gondwana which 40 million years ago was a supercontinent that joined South America and Australia. In each place inhabitants live because they are adapted to their land. But also huge changements occured all along the years since the very first species, due to those geological relations. We name it the biogeography. Nowadays, we justify biogeography with two important developements:

-The molecular taxonomy is an accumulation of DNA informations that can tell us the evolutionnary relationship between species and also the approximate times when they diverged from their common ancestors. The change of DNA sequences shapes helps us estimating the divergence times of species in poor fossil records. -Continental drift, which is the past movements of continents.

We'll notice that natural selection is different on continents and on islands. Every theory-most of them are Darwin's-developped in our chapter contradicts the ideas of creationism, and proves that evolution can be justified by natural selection.

== co [[ Utilisateur:Pierre.brawand|Pierre.brawand]] 19 avril 2011 à 22:45 (CEST)

Continents

What is convergent evolution?

Convergent evolution explains how two differents spieces that live in similar habitats can look and behave in the same way , because of similar selection pressures from their environment.
Convergent evolution proves three evolutionary theories:

1. Common ancestry, which explains the features shared (or not shared) between two infraclasses of mammals.

2. Speciation is the process by which a common ancestor can generate several different offsprings.

3. Natural selection expresses how each spieces adapted to its own environment.

How can similar species live in similar habitats but on different continents?

The continental drift explains this particularity. Million years ago, the continents weren't situated as they're now. It was attach into one landmass. Which means that some place in our actuals continents contain the same habitats but are now in completly differents places on the earth. It explains the fact that species or plant living in one area should be the descendants of earlier species that lived in the same place. The organisms continued to evolve even if they weren't living in the same place anymore. The habitats staid similar in differents continents, for example Africa and South America were part of the Gondwana. To be precise the organisms disperse and colonize a new area and finally can evolve. Tha's why there should be descendants. The common ancestor is directly link to the explanation of descendants of similar species in similar environment.

Islands

Darwin realised that islands play a very important role in the theory of evolution. Before we got to this evidence, we have to distinguish two types of islands: the continental and the oceanic ones.

What is a continental island?

It's an island which was once connected to a continent but was separeted from it either with the increase of sea levels which formed a barrier or by moving continental plates. Examples: Madacascar, Great Britain.

What is an oceanic island?

This kind of island was never connected to a any continent. They came out of the seafloor "beneft of life", as for instance growing volcanoes. Examples: Hawaïan Islands, Galàpagos Archipelago.

What are the main differences between continental and oceanic islands?

There are many types of native species we can oberve on continents and continental islands that are absent on oceanic islands. Darwin "noticed" that this was hard to explain from a creationist point of view, because the question would be why would a creator put some species on certain islands and not on others? Moreover, why should the way in which the island was created make a difference? Particularly, on oceanic islands live small flowering plants that can evolve into trees.

AllanP 5 avril 2011 à 14:37 (CEST)
EstelleV 5 avril 2011 à 14:49 (CEST)
HéloiseD 7 avril 2011 à 11:09 (CEST)

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