Unit 5

• Unit 5 is titled "Evolution and Adaptations" and all topics are part of the Biology course

Evolution

• Present-day species have arisen by change from ancestral forms of life
• 'Evolution' refers to the gradual development of something
• Evolution of species means the gradual development of life over long periods of geological time
• Evolution is the development of new types of living organisms arising from pre-existing ones through the build-up of genetic differences Occurs with changes to heritable characteristics of species

Types of Evolution

• Divergent evolution is the accumulation of differences between closely related populations resulting in speciation
• Convergent evolution is the independent evolution of similar features in species from different periods
• Convergent evolution creates analogous structures that have similar form/function, but not from a common ancestor
• Parallel evolution is similar trait development in distinct, unrelated species sharing a similar original trait responding to similar evolutionary pressure

Evidence of Evolution

• Evolution is supported by strong evidence, even though it cannot be definitively proven
• Fossils document the existence of extinct species related to present ones

Anatomy

• Species share physical features if a common ancestor had the feature
• Homologous structures are an example, like pentadactyl limbs

Molecular Biology

• DNA and genetic code reflect shared ancestry with related species having the 'same' gene inherited from a common ancestor
• Humans, cows, chickens, and chimpanzees share the insulin-encoding gene through common ancestry
• Amino acid sequences compare distantly related species and DNA/RNA base sequences compare closely related organisms

Biogeography

• The global distribution of organisms and unique island species features reflect evolution/geological change
• Adaptive radiation is the diversification of an organism group into forms filling different ecological niches
• A niche is how an organism fits into its ecological community and ecosystem

Pentadactyl Limbs

• Four vertebrate groups have limbs: amphibians, reptiles, birds, and mammals
• These groups use limbs for walking, jumping, swimming, climbing, and digging
• The basic bone structure is the same and known as the the pentadactyl limb
• The most plausible explanation is that these vertebrates share an ancestor that had pentadactyl limbs
• Groups have divergently evolved from a common ancestor, limbs developing differently to suit locomotion
• Homologous structures like the pentadactyl limb evolved from a common ancestor
• Vestigial structures are homologous to important structures but have lost their major ancestral function
• The tailbone of humans, hind leg bones of whales, and underdeveloped snake legs are vestigal Structures
• Physical features that look alike aren't necessarily marks of common ancestry
• Analogous structures evolved independently in different organisms because of similar environment/selective pressures
• Convergent evolution leads to similar structures

Clades

• Structural traits aren't commonly used to determine a clade, a common ancestor's evolutionary descendants
• Molecular biology (amino acid sequencing, DNA comparison) are used instead
• Prevents classifying animals that look physically alike
• Molecular evidence has revealed sharks and dolphins, though similar in appearance, are evolutionary distinct
• Sharks and dolphins share fins and live-in aquatic environment, and are mis commonly placed together in the same clade.

Natural Selection and Variation

• Natural selection can only occur if there is variation among members of a species.
• Variation describes differences in a population being both inherited and acquired
• Plants and animals from sexual reproduction show parental variation
• Natural selection results in an organism adapting to the environment via selectively reproducing changes in its genotype/genetic make-up
• Organisms reproduce and produce many offspring, but not all survive due to competition for resources and a struggle for survival
• Individuals with favorable characteristics survive better and have an advantage over their peers
• A lion cub with bigger leg muscles can run faster and get food easier than its siblings
• Individuals best adapted to challenges survive to adulthood
• Surviving adults breed, increasing the likelihood of advantageous alleles being passed on, resulting in better adapted offspring

Sources of Variation: Mutation

• Mutation is the original source of variation
• New alleles are produced by gene mutation, enlarging a population's gene pool

Sources of Variation: Meiosis

• Meiosis produces new allele combinations via breaking up existing combinations in a diploid cell - random assortment of homologous chromosomes
• Every cell produced by meiosis probably carries a different allele combination

Sources of Variation: Sexual Reproduction

• Sexual reproduction involves the fusion and crossing-over of male and female gametes
• Offspring get a combination of alleles from two parents that contributes significantly to variation between generations and species

Theory of Evolution by Natural Selection: Charles Darwin

• Charles Darwin developed the theory of evolution by natural selection to explain how changes in species occurs through natural selection
• After 20 years of research, he wrote The Origin of Species that changed how biologists viewed the living world and humans
• On the Galapagos Islands, Darwin saw variation and that populations produce more individuals than can survive due to limited resources
• There was a 'struggle for existence' with only the most fit surviving
• Upon returning to the UK, Darwin developed his Natural Selection Theory

The Theory of Evolution by Natural Selection: Points

• Species tend to produce more offspring than the environment can support (population number)
• There is a struggle for existence in which some individuals survive and some die (competition)
• Natural populations have variation between the individuals (variation)
• Some individuals are better adapted than others with adaptation being a characteristic making an individual suited to its environment (fitness / differential survival)
• Individuals better adapted are more likely to survive and have offspring while less adapted ones are less likely to survive and may produce fewer offspring (fitness / differential reproduction)
• Individuals that reproduce pass on their more fit genotypical characteristics to their offspring (inheritance)
• The frequency of characteristics making individuals better adapted increases and the frequencies of other characteristics decreases resulting in species changing and becoming better adapted (accumulative change)

Niche

• The niche is the way an organism fits into an ecological community or ecosystem
• Every species has a unique niche
• Populations move to new environments the niche can change
• As niche changes, so does the species
• If a species' niche is not capable of change the species is unable to survive
• Note: A species survival is the capacity of a species to reproduce and produce offspring

Evolution: Darwin vs. Lamarck

• Lamarck's theory based evolution on how organisms change during their lifetime before passing these traits onto offspring
• Lamarck thought giraffes had long necks because they stretched to reach leaves in high up trees, where each generation of giraffe had a longer neck than previous generations
• Lamarck believed there to be no difference between inherited and acquired adaptations and that evolution was organisms gaining the characteristics to better their environment
• Darwin's theory refuted Lamarck
• Darwin believed organisms had variation and these variations led to some being more likely to survive and reproduce than others
• Features that made an organism more likely to survive were likely to appear in each generation

Natural Selection

• Darwin's theory would suggest some giraffes had longer necks to begin with, allowing them to eat from taller trees
• Because of their ability to reach more food, long necked giraffes were eventually the only ones left
• According to Darwin, organisms do not acquire adaptations to better fit the changing environment, but the changing environment naturally selects those more more likely to adapt/survive
• Lamarck's theory suggests that all organisms become more complicated, which doesn't apply to single celled organisms
• Traits acquired during an individual's lifetime are not passed onto offspring

Selective Breeding

• Selective breeding are domesticated breeds - animals/plants - developed from wild species
• Breeds developed by selecting individuals with desirable traits and breeding them
• Differences in heritable characteristics of domesticated breeds show that species can evolve rapidly via artificial selection
• Humans use Selective breeding to produce a variety of animals and plants that have an increased economic importance
• It is considered a safe way of developing new organism strains and is faster than natural selection

Points on Selective Breeding

• Wild variety plants are resistant to fungal diseases but have poor fruit yield
• Crossbreeding wheat plants over generations and selecting for the best features can create varieties that are both disease resistant and have high seed yields
• Crossbreeding is producing offspring via mating purebred individuals from different breeds, varieties, and species
• One cattle variety might have a higher than average silk yield while another has a very high meat yield
• If these cattle varieties are cross bred, individuals in the next generation with desired features will be selected for continued breeding until a new breed is artificially produced that has both (high milk production and high meat yields)
• Selective breeding removes variation from a population
• This leaves selective bred species susceptible to disease, while being potentially at risk of exctinction

Speciation–Adaptive Radiation

• Speciation/natural selection occur to form new species
• Speciation is the process where a species population(s) become different enough to form a new species
• Speciation may occur when geographical isolation occurs due to predation, gradual environmental changes and/or abrupt environmental changes

Allopatric Speciation

• Allopatric [(allo) other + (patric) place] speciation occurs when members of a population become geographically separated and genetic exchange is prevented
• Results from geographical changes (formation of a mountain by volcanoes, island formation, habitat separation by glaciers/rivers) or by human activities
• It may also result from some species members emigrating causing population separation by dispersal
• Adaptive radiation is allopatric speciation in a relatively short evolutionary timeframe

Adaptations

• Adaptations make an organism suited to live in its environment
• The answer to these questions takes us back to the evolution of the species themselves
• Organisms have gradually changed and were modified to live in their environment
• Different species have passed different survivability traits in the time and place the organisms are living (natural selection and evolution)
• Adaptations are the traits that make organisms well suited to live in their habitat, in evolutionary theory, Adaptation is the biological mechanism by which organisms adjust to new environments or to changes in their current environment

Three Ways Organisms Adapt to Different Environments: Behavioral Adaptations

• Behavioral Adaptations are actions causing a organism to survive in their environment
• Adaptions are from environment change or actions of another species
• Predatory animals might start hunting packs (an evolutionary advantage over solo hunters), or there maybe changes in social patterns, communication methods, feeding habits, and reproductive strategy
• Bears hiberate in winter for example, to escape the cold temperature while preserving energy

Three Ways Organisms Adapt to Different Environments: Structural Adaptations

• Structural Adaptations are the physical features of an organism to enable it to survive in its environment
• Environmental changes may cause animals to develop suction pads/climbing claws
• Other structural changes include developing wings for flight, fins for swimming, powerful legs for jumping
• Penguins and whales have blubber to protect themselves from freezing

Three Ways Organisms Adapt to Different Environments: Physiological Adaptations

• Involve Internal and/or cellular features of an organism that enable them to survive in their environment
• Physiological adaptations are similar to structural adaptations
• This type of adaptation may be driven by changes to the environment or the behavior of another species
• Species living in water may adapt by slowly shifting its own body chemistry

Physiological Adaptations Examples

• Plants secrete toxins to prevent being eaten
• Snakes produce poisonous venom to ward off predators and to capture prey
• Embracing evolution can make it tempting to view every trait as an adaptation, however many organisms didn't develop their traits to better survive/pass on genes, it may have been happenstance of history

Surface area to volume ratio (SA:V)

• The amount of surface area per unit volume of an object or collection
• Surface area refers to the cell's outside area (units²)
• Volume refers to the amount of space inside the cell (units³)
• The outside surface of a is cell membrane, where substances pass in and out, and if surface area is increased than more will pass in and out
• After entering the cell, substances can move into the cytoplasm to be used in processes like respiration
• Internal volume must be adequate and if volume is increased, it will take longer for substances to get to the center, making balance vital to the cell's requirements
• As cells grows, volume (units³) increases faster than surface area (units²), leading to a decreased SA:V ratio

Cell Size

• Cells use diffusion to get substances in and out
• When a cell grows, the membrane has comparatively less resulting in the substances not reaching the entre of the cell
• Diffusion is less effiicient and cell processes slow
• The cell divides and it may slow down metabolism
• Cell must then divide into two smaller cells, which each of the smaller cells have larger SA:V making diffusion work more efficient again

SA:V Ratio: Unicellular / Multicellular Organisms

• Unicellular organisms have a small size which gives them a large SA:V ratio
• Large SA:V ration is adequate for materials to pass in and out, limiting the organisms size
• Multicellular organisms overcome this by being multicellular, cells also evolve features to work with the ratio, such as the gas exchange organs and blood.

Specialized Structures in Larger Animals

• Adaptations may be outwardly visible, while others are hidden within the body
• Outside the body adaptations can include temperature control, defense against parasites, defense against poisonous plants, defense against sunburn, defense against predators, warning to predators, mimicry, camouflage from predators, deceiving predators, and attraction of a mate
• Within the body is oxygen, glucose are needed for cellular respiration, a variety of nutrients, and by having these things, the organism is more able to uptake the substances it needs

Diffusion / Specialized Structures

• Diffusion is the molecules of movement to lower concentration and various factors can speed up the rate:
• Increasing surface area: The larger area with an example of folds within the small intestine
• Decreasing the thickness of the diffusion area: a small diffusion distance is needed
• Maintaining a concentration gradient: A higher concentration in the alveoli will ensure molecules can move properly