15-2 Theories of Evolution

Biological EvolutionChange of populations of organisms over generations.

Jean Baptiste de LaMarck (1780)

First to propose a hypothesis of species modification.

Similar species descended from a common ancestor.

He said acquired traits were passed on to offspring.Acquired traits are traits which are not determined by genes but by experience or behavior of an organism. These traits cannot be passed on.

  Baptiste studied the webbed foot of water birds. He thought that the offspring would also have webbed feet because of acquired traits. This hypothesis was rejected but was a forerunner for evolution.Charles Darwin came along 50 years later and presented a better case for evolution.

Jean Baptiste de LaMarck

Charles Darwin (1823-1913)   Proposed hypothesis that

species were modified by natural selection.

*Natural selection deals with genetics. It says organisms that are best suited to their environment are best able to reproduce and have more offspring.

  He published a book called “The origin of the species” in 1859 which announced his hypothesis.

  He was English. He was hired to go on the H.M.S. Beagle as a naturalist. This ship traveled to S. America, Europe, Australia, and Africa for 5 years.During the 5 years, he collected many different types of fossils and observed thousands of species.

Map of Beagle

Charles Darwin

Analysis of Data

Collected 13 similar but separate species of finches from the Galapagos Islands. He said they all came from 1 female finch over time.

Origin of SpeciesTook

Darwin 21 years to publish this book.It was on evolution by natural selection.

Darwin’s Finches

Darwin’s Theories

2 theories 1. Evolution occurs “Descent with

modification”. 2. It is caused by natural selection.

1. Descent with Modifications

Newer forms in the fossil records are just modified forms of older forms.

Similar organisms arise in the same geographic location.Organisms give rise to similar organisms.

2. Modification by Natural Selection

States how evolution occurs.  Darwin influenced by Thomas Malthus.  Said that populations could grow unchecked

(meaning they could get bigger and bigger) but they do not because of deaths due to sickness, environmental conditions, reproduction rates, etc. However, some organisms have traits which help them survive.

Traits   If it increases the reproductive success and

is inherited then the trait will be passed on to many offspring

  As favorable genes increase, a population of organisms will adapt to its environment

   Individuals with highest fitness will adapt well to its environment and reproduce more successfully then an individual with low fitness.