Question

In "why the evolution is true"What type of mammals were discovered on the islands and why are they important?

Answer 1

Evidences of evolution

Species have evolved from a common ancestor, rather than created separately. Evidences supporting the evolu­tion model come from multiple, distinct areas of biology and geology. These pieces of evidence can be grouped into four categories:

• Direct observation of evolutionary change
• Homology and development
• Vestigial traits

• Fossil record and biogeography

Direct observation of evolutionary change

Small-scale evolution can be observed in nature or generated experimentally in the laboratory. The classic story of the peppered moth in Britain during the industrial revolution is an example of microevolution. Grant and Grant have recorded evolutionary change in beak shape within and among populations of Darwin's finches, over periods as short as two years.

We can also drive genetic change in laboratory populations of Drosophila and other model organisms in the laboratory. By selecting certain phenotypic traits, we can generate directional change in characteristics such as abdominal bristle number, lifespan and avoidance to certain chemicals. Artificial selection experiments are also the foundation of agricultural improvement over the past 10,000 years.

Homology and development

One of the most compelling lines of evidence supporting the common ancestry of species is that of similar structural elements across functionally diverse forms. It becomes evident from comparative anatomy. We find the same bones in many different types of animals, but these bones are often modified to do different things. The hopping legs of the frog contain the same bones as our own legs, but the frog's legs are highly modified to fulfil a different function (hopping). The wing of a bird and the forelimb of a bat contain exactly the same bones as the arm of a human, but the size shape, and even internal structure of these bones are all adapted to play a different role in each animal.

We call structures like the wings of a bird and the forelimbs of a bat homologous structures. Homologous structures are structures that are derived from a common ancestor. Even if they are superficially different, they are developmentally related. Homology does not mean that these structures must share the same function. A character shared between two species but not present in their common ancestor or is called homoplasy.

But very often in nature we find structures that are superficially similar, even though the organisms are completely unrelated to one another. These structures may even serve the same function, like flying and described as analogous structures. The wing of a bird and the wing of an insect are good examples of analogous structures. In every physical and biological way, these wings are radically different from one another. One is a flat plane of exoskeletal material and the other is a chordate forelimb shaped into an airfoil with hollow internal bones and an outer covering of feathers. But they can both be used to fly.

The observations of structural homology support the causal hypothesis of evolutionary homology: that the common structural organization results from common ancestry. The evidence of analogous structures further supports the evolutionary homology concept, as they indicate that design is not necessarily constrained (that is, there's more than one way to build a functional part). In many cases, during embryonic development of organism, the embryo exhibits characteristics of the embryos of its ancestors. For example, early in their development, human embryos possess gill slits like a fish, and later exhibit a tail, the vestige of which presents in adulthood as a coccyx at the end of spine. These relict developmental forms suggest strongly that our development has evolved.

Vestigial structures

Many species show structural or genetic features that serve no apparent function. Obvious examples of these include the presence of pelvic bones in snakes and whales, rudimentary eyes in some cavefish species, presence of the nictitating membrane in human and the presence of pseudogenes throughout the genomes of eukaryotes. These structures suggest strongly that the species has changed over time, and descended from an ancestor with different ecological or genetic characteristics.

A related phenomena suggesting descent with modification is evidence of poor engineering or inefficient design in some characteristics of organisms. For example, gene regulation is often a very inefficient process with multiple (often conflicting) stages. These observations suggest that existing structures are often co-opted during evolutionary change to serve new functions (that is, there is descent with modification as opposed to independent design of each species).

Fossil record and biogeography

Fossils are the preserved remains or traces of organisms from the distant past. The fossil record remains first and foremost among the databases that document changes in the past life on the Earth. Sedimentary rocks are the richest source of fossils. As a result, the fossil record is based primarily on the sequence in which fossils have accumulated in sedimentary rock layers called strata. The fossil record shows that there have been great changes in the kinds of organisms that dominated life on the Earth at different points in time. The fossil record of most major animal groups begins in the Cambrian.

Biogeography is the science that explains the distribution of species, and higher taxa, on the surface of the Earth. Geographic distributions of species may be endemic (species that are limited to a particular area), cosmopolitan (species that are found on all continents of the globe) or disjunct (species that are not confined to a single area, but are distributed in more than one region with a gap between them). The biogeographic distribution of species supports evolution. For example, approximately 2,000 species of flies belonging to the genus Drosophila are now found throughout the world. About one-quarter of them live only in Hawaii. Similarly, more than a thousand species of snails and other land mollusks are found only in Hawaii. The biological explanation for the multiplicity of related species in remote localities is that such great diversity is a consequence of their evolution from a few common ancestors that colonized an isolated environment. The Hawaiian Islands are far from any mainland or other islands, and on the basis of geological evidence they never have been attached to other lands. Thus, the few colonizers that reached the Hawaiian Islands found many available ecological niches, where they could, over numerous generations, undergo evolutionary change and diversification.

In the question, the name of the islands is not mentioned, so it is not possible to answer this part of the question properly. So I mentioned about the Galapagos Islands, from which the work of Darwin's started about evolution.

Galapagos Islands and Darwin's finches

The Galapagos Islands (named after the large tortoises that inhabit them) are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador. An archipelago (sometimes called an island group) is a chain or cluster of islands. The Galapagos archipelago is a cluster of 29 islands and islets of different sizes lying on the equator. The islands are all relatively young in geological terms, and they have never been connected with the adjacent mainland of South America or with any other source area. All the organisms that occur on these islands have reached there by crossing the sea, as a result of chance dispersal in the water, by wind or by transport via another organism.

Darwin's finches are a group of 14 species of small birds, 13 of which occur on the Galapagos Islands. This group of birds provides one of the most striking and best-studied example of evolution on the islands. Scientists think that Galapagos finches descended from an ancestral species that originally inhabited the mainland of South America. Since the Galapagos is a group of islands, small flocks of birds could occasionally reach new islands where no of her land birds were present. On these new islands the immigrants would become adjusted to the local conditions through the process of natural selection. The descendants of the original finches that reached the Galapagos Islands now occupy many different kinds of habitats on the Islands. In doing so, they would have become progressively more different from the original populations. The most obvious difference between these finches relates to dietary adaptations and is reflected in the size and shape of their beaks. The finches of the Galapagos Islands provide an example of adaptive radiation - the formation of new forms from an ancestral species, usually in response to the opening of new habitats. Among the 13 species of Darwin's s finches that inhabit the Galapagos, there are three main groups:

Ground finches

There are six species of ground finches. Most of the ground finches feed on seeds of different sizes. The size of their beaks is related to the size of the seeds on which the birds feed.

Tree finches

There are six species of tree finches, belonging to several diverse groups. These species also differ from one another primarily in beak size and shape, which reflect adaptations to their food. Four species have beaks that are suitable for feeding on insects; the ones with larger beak feed on larger insects, and those 3 with smaller beaks feed on smaller insects. One of the tree finches has a parrot like beak; it feeds on buds and fruits in the trees. The sixth species of tree finch, the woodpecker finch, has a chisel-like beak. This unusual bird carries around a twig or a cactus spine, which it uses to probe for insects in deep crevices. It is an extraordinary example of a bird that uses a tool.

Warbler finches

This unusual bird differs from the ground finches and the tree finches in its habits and morphological adaptations. The warbler finch plays the same ecological role in the Galapagos woods that warblers play on the mainland, searching continually over the leaves and branches for insects. It has a slender, warbler like beak.