The Wallace-Darwin Theory

Date: 2015-10-07; view: 421.

The Darwin Theory

Thesynthetic theory of evolution

Jean Baptiste de Lamarck (1744-1829) developed one of the first theories on how species changed. The idea (given voice by Lamarck) that species could change over time was not immediately acceptable to many: the lack of a mechanism hampered the acceptance of the idea, as did its implications regarding the biblical views of creation. Charles Darwin and Alfred Wallace both worked independently of each other, traveled extensively, and eventually developed similar ideas about the change in life over time as well as a mechanism for that change: natural selection.

1. Adaptation: all organisms adapt to their environments.

2. Variation: all organisms are variable in their traits.

3. Over-reproduction: all organisms tend to reproduce beyond their environment's capacity to support them.

4. Since not all organisms are equally well adapted to their environment, some will survive and reproduce better than others - this is known as natural selection. Sometimes this is also referred to as "survival of the fittest".

1. Individuals in a population have variable levels of agility, size, ability to obtain food, and different siccesses in reproducting.

2. Left unchecked, populations tend to expand exponentially, leading to a scarcity of resources.

3. In the struggle for existence, some individuals are more successful than others, allowing them to survive and reproduce.

4. Those organisms best able to survive and reproduce will leave more offspring than those unsuccessful individuals.

5. Over time there will be heritable changes in phenotype (and genotype) of a species, resulting in a transformation of the original species into a new species similar to, but distinct from, its parent species.

Neither Darwin nor Wallace could explain how evolution occurred: how were these inheritable traits (variations) passed on to the next generation? (Recall that Gregor Mendel had yet to publish his ideas about genetics). During the 20th century, genetics provided that answer, and was linked to evolution in neoDarwinism, also known as the Modern Synthesis(synthetic theory of evolution).

Thesynthetic theory of evolution as described by Sewell Wright attempts to explain evolution in terms of changes in gene frequencies. This theory states that a species evolves when gene frequencies changes and the species moves it to a higher level of adaptation for a specific ecological niche. This is essentially a combination of Charles Darwin's concept of natural selection, Gregor Mendel's basic understanding of genetic inheritance, along with evolutionary theories developed in the 20th century by population geneticists and molecular biologists.

The main postulates of Modern Synthesis(synthetic theory of evolution) are following:

1. A biological species consist great number of units – subspecies and populations.