Evolution - Chapter 7

natural selection

natural selection

• the process by which characteristics of a population change over many generations as organisms with heritable traits survive and reproduce, passing their traits to offspring.

• is the mechanism by which populations change. Individuals within a population may survive if they have an inherited trait that gives them a selective advantage. They can then go on to reproduce and pass on their advantage to their offspring.

artificial selection

directed breeding in which individuals that exhibit a particular trait are chosen as parents of the next generation

neutral mutation

a mutation that does not result in any selective advantage or disadvantage

harmful mutation

any mutation that reduces the reproductive success of an individual and is therefore selected against; harmful mutations do not accumulate over time.

example: include those that lead to serious genetic disorders such as cystic fibrosis or Huntington’s disease

Beneficial mutation

any mutation that increases the reproductive success of an organism; beneficial mutations are favored by natural selection and accumulate over time.

• give individuals a better chance of survival in their environment.

mutations

• create new genes that provide a continual supply of new genetic information.

• mutations that enter populations have an immediate and direct effect on individuals and also have the potential to influence future generations when those mutations are inherited.

• most are neutral and result in changes in DNA that have no immediate effect.

Selective pressure

environmental conditions that select for certain characteristics of individuals and select against other characteristics.

The domesticated plants and animals

• provides humans with the vast majority of our food supply and formed the basis for the development of modern civilizations

Domestication

• is the changing of members of a species to suit human needs through controlled captive breeding - this process is referred to as artificial selection

How does artificial selection work?

• the breeder usually has a particular feature in mind

• generation after generation, farmers selected seeds from the best plants to sow the next season

• the seeds germinated, grew, flowered, and then cross-pollinated one another, producing more fruit with the desired traits.

The power of Artificial selection

• can produce surprising results

• such as individuals that exhibit traits that are far beyond the natural variability witnessed in the original breeding population.

• can reduce genetic diversity within a population

what happens if breeders favour only certain traits within a population?

• the many alleles linked to other versions of a particular characteristic are reduced or eliminated

• such a loss in diversity makes a population more vulnerable to disease.

Why can breeders not create traits that do not already exist in some form within the population?

• if there are no genes for an organism, then no amount of crossbreeding will create one.

• breeders must work with the genetic diversity that already exists in the population or resort to genetic engineering technology to alter it.

why do beneficial or neutral mutations have a good chance of being passed on to future generations?

• they are either favored or go unnoticed.

• in contrast, mutations that cause harm, or produce an undesirable trait in an individual, have little influence on the potential success of artificial selection efforts.

• breeders do not choose such individuals for breeding, and therefore the harmful mutations are not passed down.

Fitness

the relative contribution an individual makes to the next generation by producing offspring that will survive long enough to reproduce.

Biotechnology

the use of technology and organisms to produce

The key difference between natural and selections

• that in natural selection, the environment plays the role that we play in artificial selection

monoculture

• extensive plantings of the same varieties of a species over large expanse of land

• is the agricultural practice of planting large expanses of uniform varieties of the same species. Monoculture is risky because the organisms are so similar that they could all be killed or damaged by a new pest.

Disadvantages and advantages of monoculture

• Disadvantages: lack of genetic variation

• easy to attack

• Advantage: makes carrying of the field easier

Gene banks

• environmental conditions that select for certain characteristics of individuals and select against other characteristics.

paleontology

the study of ancient life through the examination of fossils. Include specimens preserved in amber, permafrost, dry caves & rock

George Cuvier

(1769-1832) – “father of paleontology”

• catastrophism

Charles Lyell

(1797-1875) – “father of modern Geology”

• Uniformitarianism

Catastrophism

the theory that the pattern of fossils could be accounted for by a series of global catastrophes that wiped out most species on Earth.

Uniformitarianism

the theory that geological changes are slow and gradual, and that natural laws and processes have not changed over time

Cuvier - catastrophism

• strata contain unique fossil species

• deeper, more dissimilar

• found evidence that new species appeared and others disappeared over time (Evidence of Extinction)

Lyll- Uniformitarianism

• geologic processes work the same now as in the past

How fossils are formed?

• animal dies and the body sinks into the bottom of the water

• the remains of the body start to rot and get covered with mud

• over time layers of sediments cover the bones

• the sediments causing the bones to harden into rock

• as the bones slowly decay, minerals filter down into space and replace the chemicals in the bones

• layers of rock get worn away by wind and rain (erosion)

• an allosaurus fossil is discovered!

Reading the fossil record

● Many fossils appear to be of unusual and unknown organisms. There are fossils of thousands of species that are no longer living. ● There are no fossils of most living species. ● Fossils are often buried very deep within rock formations. Some are more than a kilometre below Earth’s surface. ● Fossils are often found in unexpected locations. For example, fossils of sea life are found high in mountain formations and in present-day deserts.

population

population is a multiple of the same species

community

a community is many of different species

Jean- Baptiste Lamarck (1744-1829)

• Idea of Use and Disuse…structures used became larger and stronger, while structures that were not used became smaller and weaker.

Inheritance of Acquired Characteristics

• individuals passed on to the offspring characteristics they had acquired during their lives.

Despite Lamarck’s flawed theory, he did contribute to the understanding of evolution:

• All species evolve over time

• A species evolves in response to its environment and becomes better adapted to that environment

• Changes are passed on from generation to generation.

immutable

unable to change

fossil

any ancient remains, impressions, traces of an organism or traces of an organism or traces of its activity that has been preserved in rocks or other mineral deposits in Earth’s crust.

1. fossil record

the remains & traces of past life that are found in sedimentary rock; it reveals the history of life on Earth & the kinds of organisms that were alive in the past.

a) evidence from the fossil record

• fossils found in young layers of rock are much more similar to species alive today than fossils found in older, deeper layers of rock

• fossils appear in chronological order in the rock layers

• not all organisms appear in the fossil record at the same time

b) evidence from transitional fossils

transitional fossils: a fossil that shows intermediary links between groups of organisms & shares characteristics common to two now separate groups

Vestigial structure: a structure that is a reduced version of a structure that was functional in the organism’s ancestors

biogeography

biogeography: the study of the past & present geographical distribution of species population

2. Evidence form Biogeography

a) geographically close environments are more likely to be populated by related specie environmentally than are locations that are geographically separate but environmentally similar.

b) animals found on islands often closely resemble animals found on the closest continent

c) fossils of the same species are almost never found in exactly the same location or habitat.

3. Evidence from Anatomy

a) homologous structure: structures that have similar structural elements & origin but may have a different function

ex: the human hand, compared to the found in a frog, bat, or horse

b) analogous structure: structures of organisms that do not have a common evolutionary origin or anatomical structure but perform similar functions (ex: bird and insect wings)

4. Evidence from Embryology

embryology: the study of early, pre-birth stages of an organism’s development

Ex: all vertebrates have paired pouches of the throat…in fish & some amphibians, the pouches develop into gills … in humans, the pouches become parts of the ears & throat

5. Evidence from DNA

If two species have similar patterns in their DNA, this indicates that these DNA sequences must have been inherited from a common ancestor.

homologous feature

a structure with a common evolutionary origin that may serve different functions in modern species (for example, bat wing and human arm)

analogous feature

a structure that performs the same function as another but is not similar in origin or anatomical structure; for example, bird and insect wings

abiogenesis

the origin of life from non-living matter

coevolution

a process in which one species evolves in response to the evolution of another species.

example:certain plants have evolved hard protective shells to protect their seeds, while some seed-eating mammals have evolved powerful jaws and teeth for chewing through hard shells.

reproductive isolating mechanism

any behavioural, structural, or biochemical trait that prevents individuals of different species from reproducing successfully together.

prezygotic mechanism

a reproductive isolating mechanism that prevents interspecies mating and fertilization

5 conditions that result in evolution

• natural selection: favours the passing on of some alleles over others

• small population size: increases the likelihood of genetic drift

• mutation: introduces new alleles to a population

• immigration or emigration: introduces or removes alleles in a population

radioisotope

an atom with an unstable nucleus that is capable of undergoing radioactive decay.

hardy weinberg principle

in large populations in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation

gene pool

the complete set of all alleles contained within a species or population

directional selection

selection that favours an increase or decrease in the value of a trait from the current population average

stabilizing selection

selection against individuals exhibiting traits that deviate from the current population average

genetic drift

changes to allele frequency as a result of chance; such changes are much more pronounced in small populations

founder effect

genetic drift that results when a small number of individuals separate from their original population and establish a new population.

genetic bottleneck

a dramatic, often temporary, reduction in population size, usually resulting in significant genetic drift.

transitional form

a fossil or species intermediate in form between two other species in a direct line of descent

microevolution

changes in gene (allele) frequencies and phenotypic traits within a population and species

speciation

the formation of new species

reproductive isolating mechanism

any behavioural, structural, or biochemical trait that prevents individuals of different species from reproducing successfully together

prezygotic mechanism

a reproductive isolating mechanism that prevents interspecies mating and fetilization

for ex: ecological isolation, temporal isolation, and behavioural isolation)

postzygotic mechanism

a reproductive isolating mechanism that prevents maturation and reproduction in offspring from interspecies reproduction.

allopatric speciation

the formation of a new species as a result of evolutionary changes following a period a geographic isolation.

sympatric speciation

the evolution of populations within the same geographic are into separate species

adaptive radiation

the relatively rapid evolution of a single species into many new species, filling a variety of formerly empty ecological niches.

divergent evolution

the large-scale evolution of a group into many different forms

convergent evolution

the evolution of similar traits in distantly related species

coevolution

a process in which one species evolves in response to the evolution of another species.