Evolution

Evolution is the process by which species of organisms change over time through the gradual accumulation of minor genetic variations. The fundamental concept of biology explains the diversity of life on Earth.

Theories of Evolution

There are two main theories of evolution:

1. Darwin's Theory of Natural Selection: This theory proposes that organisms that are better adapted to their environment are more likely to survive and reproduce. Over time, this leads to the evolution of new species.

2. Lamarck's Theory of Inheritance of Acquired Characteristics: This theory proposes that organisms can pass on traits that they acquire during their lifetime to their offspring. However, this theory has been largely discredited by modern science.

Evidence of Evolution

There are several lines of evidence that support the theory of evolution:

1. Fossil Record: The fossil record shows a progression of life forms from simple to complex over time.

2. Comparative Anatomy: The similarities and differences in the anatomy of different species provide evidence of common ancestry.

3. Molecular Biology: The similarities and differences in the DNA of different species provide evidence of common ancestry.

4. Biogeography: The distribution of species worldwide provides evidence of common ancestry and evolution.

Mechanisms of Evolution

There are several mechanisms of evolution:

1. Natural Selection: The process by which organisms that are better adapted to their environment are more likely to survive and reproduce.

2. Mutation: The process by which genetic variations occur.

3. Gene Flow: The movement of genes between populations.

4. Genetic Drift: The random fluctuations in the frequency of genes in a population.

Natural Selection

• the idea that certain animals were better suited to survival and that helped them live and have offspring

  • only happens when one organism has an increased chance to spread its genes

fitness - the probability that an organism will pass on its genes to the next generation

• increased fitness - have a larger chance of passing their genes

• decreased fitness - have a smaller chance of passing their genes

Overproduction

The idea that some offspring don’t survive to meet maturity and cannot contribute their combination of genes

• ex. wild octopus, more are produced each year than that survive

• most animals can produce more offspring that can survive until maturity

  • means some offspring will die when young

    • they would not be able to pass on their DNA to the new gene pool

Genetic Variation

• helps deterime how natural selection proceeds

  • tends to select for certain traits and have certain other traits die out

• range in traits is another name for genetic variation

Adaption

• more frequent that a trait in a population the better chance that the population will survive

  • Adaption is a trait that makes an individual more likely to survive in an environment

    • ex. thick fur in cold environment vs. thick fur in a warm environment

Artificial Selection

• the process of humans selecting individual traits to give to the next generation

  • ex. when people want a certain kind of dog they will breed the dog with other dogs until desired traits are met

Populations

• a group of individuals of the same species that live in a similar area

  • isolated populations - stay by themselves, don’t have constant movement

  • fluid populations - members entering and exiting constantly

• gene pool - total of genes in a population at any given time

Micro-evolution

• devotion on a small scale that studies frequencies of alleles within a population

  • a change in alleles

    1. Mutation can change alleles by creating new alleles for the population

    2. Sexual reproduction causes an increase in the number of different traits in a population

Hardy-Weinberg

The Hardy-Weinberg principle is the equation that allows us to rest alleles in a population at equilibrium

p2 + 2pq + q2 =1

• p = dominant allele

• q = recessive allele

• can only remain constant if

  • population size is large

  • random mating is occurring

  • no mutations

  • no genes are introduced or lost

  • no selection occurs

    • means all genotypes can survive and reproduce equally well

• Helpful tips

  • p2 = WW%

  • 2pq = Ww%

  • q2 = ww%

  • p = total dominant allele percentage

  • q = total recessive allele percentage

  • p + q = 1

Genetic Drift

• the idea that chance events will cause the allele frequencies to fluctuate unpredictability

  • the larger the population, the smaller the change

  • the smaller the population the larger the change

• bottleneck effect - when a population undergoes a massive loss and only a few gentic makeups remain

• founder’s effect - when a small section of the population discovered a previously unused habitat

Types of Selection

• bell curve - a graph that shows that most organisms are similar in their genetic variations

• Stabilizing selection - favors the majority of the organisms and removes the outliers

• Directional selection - shifts the range of traits to one of the extremes

• Disruptive selection - favors the outlying individuals and removes the bulk of the population

Sexual Selection

• Darwin proposed that males and females within a population could exhibit different traits due to the fact that they are in competition for mates

  • males looking for someone to mate and then leave

  • females looking for someone with strong genes so they can put more investment

Fossils

• the remains or traces of an organism that died long ago

• superposition - the idea that the deeper a rock formation is, the older it is

• carbon dating - a measurement of how old an element is

  • allows modern day scientists to see how old the carbon in a particular fossil is

• fossil record - helps draw conclusions about the organisms on earth during different time periods

Anatomy

• the study of structures in the body

• homologous structures - anatomical structures that originated by heredity, passed by common ancestor

• analogous structures -- have closely related functions but don’t derive from similar ancestors

• vestigial structures - remains from structures long ago

Embryo Evidence

• embryo - a unborn or unhatched organism that is developing

  • that process is similar across many organisms

    • for ex. humans have tails when they first develop

• embryos don’t have structures in their final forms because they share common ancestry

Origins of Life

• stromatolites - prokaryotes that performed type of photosynthesis (Conditions of Earth)

  • ‘oldest’ organism ever found on earth, 3.5 million years old

• sexual dimorphism - 2 sexes of a species differ in external appearance , ex. male baboons are twice as large as females

• antibiotic resistance - when a bacteria changes so antibiotic medicines can’t kill them or stop their growth, ex. MRSA is resistant to 2 tuberculosis drugs, isoniazid and rifampicin.

Early Organisms

• Stanley Miller tested a hypothesis that conditions of the early earth allowed for the synthesis of organics molecules

  • modern earth doesn’t allow for the spontaneous synthesis of organic molecules because of the rich oxygen atmosphere

• Miller set a apparatus that simulated early earth w/ a “ocean, atmosphere,” and a condensing system

• collected samples form the simulated earth and found hydrocarbons and amino acids

• the results showed the molecules that make up life could have been generated from the early earth

• the conclusion also led that Earth probably isn’t the only place that could have had the conditions

Monkeys

• hominins - organisms that are closely related to a human than a chimpanzee

  • chimps are our closest relatives of the primates

• Humans are members of the order primates

  • this means we have opposable thumbs, flexible hips and shoulders, forward facing eyes, and increased sensory processing abilities

    • primates were generally found in the topical or subtropical regions of Asia, Africa, or South America

• Old World Monkeys (Asia and Africa) were the first to evolve

  • don’t have a prehensile tail and heir nostrils open downward

• New World Monkeys are found in the Americas and probably traveled to those location on logs and debris

  • they have prehensile trail, wide set nostrils, and are tree dwelling

• remaining primates are apes

• lesser apes are gibbons and Siamangs, they are considered as hylobatidae

  • are smaller, have more slender limbs, and have less sexual dimorphism than their other ape counterparts

• Great Apes are classified as the sub order homininea

  • includes orangutans, gorillas, chimps and humans

  • they all lack tails, large brain size, board flat faces, and have a socialized culture

• 20 species of hominins that have been discovered through history

• hominins appeared 7 million years ago, there were several periods where several hominin organisms appeared at once on earth

  • many died out

  • around 1 million years ago there was only one homo genus left.

The Starting Lineup

• the earliest ancestor Ardipithecus ramidus, “Ardi”

  • most famous fossil, around 4.4 million years old

  • oldest known ancestor to both chimp and humans

  • most likely lived in a forest

• the Australopithecus genus - a genus of extinct bipedal organisms with a smaller brain

  • evidence they were bipedal came from their hip joints, their spinal cord position and limb position

• the genus homo is a collection of great apes that are characterized by the evolution of larger brains

• brain size relative to body size can be an indicator of intelligence

  • it does matter how the brain is developed and shaped

Other Players (continued from The Starting Lineup)

• Australopithecus afarensis appeared roughly 4 million years ago

  • had small brains, protruding face, and walked upright

  • probably lived in small social groups like modern apes

  • most famous fossil was Lucy

  • brain cavity about 375 cc - 550 cc

• homo habillis “handy man”

  • appeared 2.2 million years ago

  • smallish size brain (510 cc - 690 cc)

  • well known for mastering a set of stone tools that allowed them to be more successful in their environment

  • thought to be a scavenger than a hunter

• homo erectus “upright man” appeared 1.9 million years ago

  • much larger brain size (940 cc avg.)

  • thought to be a hunter w/ tools to help

  • evidence of fire but no cooking

  • first evidence for leaving Africa

• homo neanderthalensis (Neanderthals)

  • had a massive brain size (1600 cc avg)

  • .3% difference in DNA (that 2x larger then the largest human gap)

  • ranged from Europe to Central Asia

  • Possible cause of many or modern traits

  • Probably driven extinct by modern humans