Evolution

Evolution -

 bonobo - chimpanzee - Human

chimpanzee and bonobo genome differ from the human genome by 1.3%

Chimpanzee genome and bonobo genome differ by 0.4%

(Social context?)(no)

Homology -

Similarity in structure and function - suggested relationships among species (common ancestor)

Paleontology - 

Suggested evolution (how different species linked to each other after extinction)

found fossils of no-longer living species

found fossils that suggested similarities between current and past species

EVOLUTION

• Changes over generations through variations in genetic traits 

• gene flow, and genetic drift, natural selection

EVIDENCE that supports evolution

1. Fossil Record - gradual changes over time, transitional fossils

2. Genetic Evidence - DNA sequencing - common genetic code

3. Comparative anatomy. - homologous structures - similar structures with different functions - common ancestors

4. Biogeography - evolution over time

5. Embryology - development of different organisms indicate common ancestry

6. Molecular Biology - proteins and genetic sequences show patterns of similarity and divergence

7. Observed Evolution - can be observed in real time, antibiotic resistance in bacteria 

Charles Darwin and Alfred Russel Wallance

Wallace - biodiversity of the Malay Archipelago. Promoted Darwin to present his own findings on evolution

Darwin's Ideas

Galapagos Islands - how finches varied from Island to Island in the Galapagis

Natural Selection

• Reproduction increases populations unless factors limit it

• individuals in a species are not identical

• Some variation among individuals is inherited

• Not all offspring survive to reproduce

• Heritable variations among individuals affect probability of surviving and reproducing

• Natural selection process by which evolution occurs

forms of natural selection

• differential survival and reproduction of organisms with heritable characteristics

• every species occupies a “niche” in enviornment or ecosystem

• survival of the fittest - how well a species or member of the species “fits” into its niche

• later added “sexual selection”

1. Variation

2. competition (food, mates, habitat are limited)

3. survival of the fittest

4. reproduction (pass on their advantageous traits to their offspring)

5. adaptation(enhance an organism’s ability to survive and reproduce in its specific environments)

Artificial Selection:

Process in which humans intentionally breed plants or animals for specific traits or characteristics. Relies on human choice to select which organisms are allowed to mate based on desired features

Sexual Selection:

Process can lead to the development of characteristics that may even be detrimental to survival but enhance attractiveness or competitiveness in mating (peacocks)

Convergence:

Similar traits or characteristics can develop separately and independently in different species in response to similar environmental challenges of ecological niches (bats and birds)

Homoplasy - similar features that evolved separately

contrast with homology - features based on common ancestry - seal’s flippers, and your arm

What is the mechanism by which organism inherit traits from their parents?

What is the source of individual variation?

Mendel - provided laws of heredity

Hugo de Vries - mutations occur - spontaneous changes in organism’s characteristics

Mechanism of inheritance - genes encoded in DNA inside all cells

• 23 pairs of chromosomes - therefore, you have two copies if each gene

Mendel’s laws of heredity

1. Law of segregation - alleles segregate so that each gamete carries only one allele for each gene

2. Law of independent Assortment - inheritance of one trait does not affect the inheritance of another when considering two or more traits. This means that alleles for different traits assort independently during gamete formation

3. Dominant and Recessive Traits - some traits are dominant, meaning they are expressed in the phenotype even when only one copy of the allele is present, while others are recessive, requiring two copies of the allele for expression

4. Phenotypic Ratios - specific ratios of traits in the offspring are observed, which indicate predictable patterns of inheritance

Mutations happen spontaneously - other traits are passed on to the offspring

 Genes among different species

• conserved - little change or difference among species (rRNA, Actin(protein, muscle contraction), Histones(proteins)) - CONSERVED - 

• considerable genetic similarities among all living cellular organisms

1. Ribosomal RNA (rRNA): genes encoding rRNA are essential for protein synthesis and are highly conserved across all domains of life

2. Actin: gene encoding actin, a protein that plays a key role in muscle contraction and cell motility, is found in nearly all eukaryotic cells

3. Histones: genes encoding histone proteins, which are critical for DNA packaging and regulation, are conserved across many eukaryotic species

Genes and Mutations

• changes in DNA can serve as a “clock” - seem to be a constant rate of DNA change (when they have evolved)

• Most changes in DNA do not affect genes

• Many changes in genes are harmless - or change nothing of significance

• A few changes are good or bad for organism

• Net result: we can use changes in DNA to estimate when two species diverged from common ancestor

Mutations that do not favor natural selection:

1. Mutations: changes to the nucleotide sequence of DNA

1. Point mutations: a single nucleotide change

2. Insertions or deletions: adding or removing nucleotides, which can lead to shifts in the genetic code

2.  Copy number variations (CNVs): variations in the number of copies of a particular gene or region of the genome. Affect traits and susceptibility to diseases

3. Chromosomal Abnormalities: involved in changes in the structure or number of chromosomes and can lead to conditions such as:

1. Down syndrome: caused by an extra copy of chromosome 21

2. Turner syndrome: Occurs when one of the X chromosomes is missing or incomplete in females

4. Epigenetic Changes: these are modifications that do not change the DNA sequence but can affect gene expression.

5.  Single Nucleotide Polymorphisms (SNPs): These are common variations in a single nucleotide that occur at specific positions in the genome. (Linked to Alzheimer’s disease risk)

6.  Genomic Rearrangements: Large-scale changes in the structure of chromosomes (these changes may lead to cancer) 

Mutation, Gene flow, and Genetic drift:

Gene Flow - gene migration, transfer of genetic materia, between populations. Populations migrate or interbreed introducing new alleles into the gene pool. Increase diversity - reduce differences between populations (important mechanism for maintaining genetic variations)

Genetic Drift - (natural disaster) - lead to production of a prominent species - reduce genetic diversity 

Classifications of species 

• 1700s

• based on animals on similarities among animals

• taxonomy

• phylogeny - evolutionary history species

• nowadays we try to classify species based on phylogenetic closeness - modern genetics aids

INVERTEBRATE VS. VERTEBRATE nervous system

Most animals - invertebrates

usually have fewer neurons but have incredible complexity in types of nervous systems

Studying other species

• Evolution explains the value in studying in other species

• how the brain has evolved

How to choose species?

• outstanding features

• convenience

• comparison

• preservation

• treatment of disease

1. What is evolution?

Where genetic makeup changes over time - how they change over time, adapt and survive in their environment

2. What is natural selection? Compare and contrast natural and artificial selection

Natural selection - survival of the fittest (Darwin)

Artificial selection - we choose(humans) what genes are passed down/ what the desirable traits are. - domesticating animals/plants 

Comparison - natural selection, environmental factors drive the selection of traits, while in artificial selection human preferences / needs are the driving forces

Similarities - both lead to changes in the genetic composition to a population over time

3. Define and contrast genetic drift and gene flow.

Genetic Drift - changes in allele frequencies in a population due to random chance

Gene flow - movement of genetic material between populations - migration/interbreeding between populations

Contrast - genetic drift, random/no specific direction while in Gene Flow it is directed by movement between populations generally reduces genetic differences

4. Why is the appearance of a new ecological niche a potent stimulus for natural selection?

1.  Resource opportunities (exploit these resources to thrive and reproduce more successfully)

2. Reduce competition

3. Environmental pressures/changes (natural disasters/climate change)

4. speciation potential (variety of species that then can develop in other conditions - divergence leading to new species)

5. Evolutionary pressure (unique challenges and opportunities presented by a new niche can drive the evolution of new traits and and adaptations)(better cope with these pressures will have a selective advantage)

6. Feedback mechanisms (organisms adapt to new their new niche - alters the environment and creates changes in their new environment - additional adaptation in the environment for other animals or just for themselves)

5. What are the theories that explain the growth of the brain (in particular cortex) in humans?

Social brain: interact in larger social groups (more cognitive abilities) - communicate effective may have saved for larger brains - better imitation/copying skills from each other - self regulate (increase brain size)

Ecological intelligence: using tools(forging for food) - environmental challenges/changes

Cultural brain: development of language - culture became more complex (also technology) - transmit that culture (pass it on)

Expanding brain: (frontal cortex) problem solving - increased cognitive demands (social complexity) - using tools

Metabolic - address energy demands of a larger brain - adapted through diet and social structures to support the metabolic costs associated with brain growth

Sexual selection - creativity is a desirable trait - find a mate - increasing of chances of reproduction 

How do we study?

• compare brains of species engaging in different kinds of behaviors

Brain structures and behavior

• amount of that particular function - how important that particular function is

Brain Structures and vertebrates

• basic similarities across vertebrate nervous systems:

development from a hollow dorsal neural tube (Animals with vertebrates)

• Bilateral symmetry

• segmentation

• hierarchical control

• separate systems (central vs. peripheral)

• Functional specialization - different regions associated with different functions

Brain Structures and Vertebrates

• brain regions functions have changed/been altered

MAMMALS - all have neocortex with 6 layers - more recent mammals have 50% of brian devoted to neocortex

Neurons in humans are much more complex than in lower animals

• Evolution, brain size, and behavior

“Bigger the brain the more intelligent” - not the case

When looking at brain size, must account for body size

Some smaller mammals have a greater brain-body ratio than humans

Encephalization factor - takes into account each class’s deviation from the center line

Tells us something about relative importance of cortex in primates in general and especially in humans - higher cognitive abilities

How do humans get such big cortices 

• regions of brain that develop later becomes the largest

• Small changes in genes causes big changes in brains

Accounts for differences

• Weights are similar

• human continues to develop after birth

• large brains in humans

genes can be differentially expressed

when genes are turned on or off or even whether they are turned on/off at all

also WHERE genes are turned on/off

When it comes to gene expression - We can see big divergence in humans compared to other primates for brain related genes

What made human brains get so big?

one hypo: social brain hypo - larger cortex to handle complex social relationships

others hyp: behavioral innovations, tool use

perhaps sexual selection - creativity was regarded as sexually desirable

most likey, multiple source of pressure favored bigger brains 

difficult to get larger brains in humans

Sexual selection and brain size

1. Cognitive abilities - larger brain size

2. mate choice

3. sexual Dimorphism

4. Social Learning

5. Human evolution