Lecture 18 - Darwinian Evolution

BIOLO

Darwin’s Premise

Organisms are well suited for their environment, rich diversity of life on earth, all life shows unity

Evolution

Descent with modification… change in the genetic composition of a population of organisms over time.

Fossils

Remains or traces of organisms from the past that are mineralized in sedimentary rocks

Paleontology

Study of fossils, developed by Cuvier

Gradualism

Major geological changes took place through the cumulative effect of slow but continuous processes that are currently going on… proposed by Hutton

Evolution by natural selection explains adaptions of organisms and the unity and diversity of life

Evolution explains?

Galapagos Islands widelife

Most animal species on the islands lived nowhere else, but resembled species living on the South American mainland… hypothosized that islands had been colonized by plants and animals from mainland…

Adaptations

Characteristics of organisms that enhance their survival and reproduction in specific ecosystems

EX: Beaks among 13 species of finches… adapt to the specific foods available on the home islands

Natural Selection

Process in which individuals with certain inherited characteristcs leave more offspring than individuals with other characteristics.

Unity of Life

Organisms are related through evolution from a common ancestor that lived in the remote past. Thus, organisms share many characteristics

Artificial Selection

Humans have modified a variety of domesticated plants and animals over many generations by selecting individuals with desired traits as breeding stock.

Darwin’s Observations of Nature

1. Members of a population vary greatly in their inherited traits

   1. All species are able to produce more offspring than the environment can support, many of these offspring fail to survive and reproduce

Darwin’s Inferences

1. Indidviduals whose inherited traits give them a higher probability of survival, reproduce more than other individuals, leaving more offspring than the other individual — these offspring bear the favorable traits that were passed on from parents

2. Unequal ability of individuals to survive, reproduce and pass on the genes for favorable traits with cause those traits accumulate over generation.

Only small fraction of offspring produced complete their development and reproduce successfully to leave offspring of their own… rest are eaten, starve, diseased, unated, or unable to tolerate physical conditions of environment like salinity (pH) or temp.

 An organism’s traits influence not only its own survival and reproductive success, but those traits are passed on to offspring thereby increasing their ability to cope and thrive.

 For example, an organism might have a heritable trait that gives its offspring an advantage in escaping predators, obtaining food, or tolerating physical conditions.

Evolution through natural selection

1. occurs between individual organisms and their environment… individuals do not evolve. Population is the smallest group to evolve over time.

2. Can act only on heritable traits

   1. Trait that is favorable in one environment may be useless in another

1. Evolution

2. Fossil Record

3. Homology

4. Biogeography

Four types of data document pattern of evolution…

Soapberry bugs feed most effectively when their beak length closely matches the size of the seed-containing fruit

Example of natural selection as a mechanism of evolution in populations

Evolution of drug-resistant pathogens… MRSA. More than 20% of S. aureus in hospitals already resistant to penicillin.

Example of natural selection as a mechanism of evolution in populations

Natural selection is an editing mechanism, not a creative force

Can only act on existing variation in the population, selects for favorale traits that are already present in the population

Homolgy

Similarity in characteristic traits from common ancestry

EX: forelimbs of humans, cats, whales, and bats

Homologous structures

similar physical features in different species that share a common ancestor

Vestigial Organs

Structures that have little to no importance in living organisms, but had important function in organism’s ancestors

EX: Leg bones in snakes and whales

Analogous Structures

traits in different species that have similar functions but evolved independently, meaning they do not share a common ancestor

Convergent Evolution

Independent evolution of similar features… organisms may resemble each other but not due to true homology

EX: Marsupial mammals from Australia resembles eutherian mammals of other continents

Fossil Record

Documents the pattern of evolution… how past organisms differ from present-day organisms and species that become extinct

EX: complete fossil record shows the early evolution of cetaceans, a mammalian order that includes whales, dolphins, and porpoises. closest living relatives of cetaceans are hippopotamuses, pigs, deer, and other even-toed ungulates.

Biogeography

Geographic distribution of species, influenced by many factors like continental drift

Pangaea

Single large continent, all of earth’s landmasses joined together 250 million years ago

Endemic species

A plant or animal species that is uniquely found in a specific geographic location and nowhere else in the world

Two islands with similar environments are populated, not by closely related species, but rather by species that resemble those of the nearest mainland.

Understanding of evolution to explain biogeographic data

Theory

More comprehensive than hypothesis, accounting for many observations and much data and attempting to explain and integrate a great variety of phenomena

Evolution can occur within a few thousand years or less.

Error with Darwin’s thought that evolution was a very slow process

Natural selection is NOT the only mechanisms invovled in process of evolution… other factors.

Factors of evolution