Comprehensive Study Notes on Evolutionary Biology: Vestigial Structures, Genetics, and Embryology

Defined as structures that no longer perform the function they originally evolved to accomplish.
These structures serve as evidence of evolution, demonstrating that organisms descended from ancestors who once possessed and utilized these features.
Many examples exist across various species, documenting the transition from ancestral forms to modern ones.

Tailbones: Humans possess internal tailbones; while they do not protrude outward as tails, they are skeletal remnants of ancestral structures.
Appendix: A structure noted as non-functional ("doesn't work") in modern humans.
Wisdom Teeth: These teeth often emerge and cause dental problems; however, they are not necessary for modern human survival or function.
Digital Webbing: - During embryonic development, humans possess webbing between their fingers. - While most people lose this webbing before birth, it occasionally persists in some individuals as webbed hands or feet.

Classification as Mammals: Whales are categorized as mammals based on two major defining characteristics: - They give birth to live babies. - Mothers possess specialized apparatus to produce milk to feed their offspring.
Vestigial Hair: Although whales typically appear to lack hair, a dissection of their skin reveals non-functional hair follicles.
Skeletal Remnants: - Deep within a whale's body, scientists find small, undeveloped pelvic bones and femurs. - These bones never grow or develop into functional limbs or hips. - This occurrence indicates that whales evolved from land-dwelling mammals, referred to as "Hashem pods" in the discussion. - These structures were not "magically created" to confuse humans but are leftovers from a terrestrial ancestor.

Polydactyly (Six Fingers): - The Question: Is having six fingers a vestigial structure from ancestors? - The Answer: No. It is not vestigial; it is a mutation or a genetic "mistake." - Context: Humans being born with six fingers is more common than generally realized, but the extra digit is usually removed at birth because it is typically non-functional. - Identification: If an individual was born with a sixth finger, parents or doctors would typically inform them; surgical scars from removal usually fade by the time someone is $16$ years old.
Tetrapod Anatomy: - All tetrapods typically have $5$ digits on each limb as their normal state. - Horses as an example: Horses evolved so that their $5$ toes fused into a single large toe, though the internal bone structure still shows the fused remains of the digits.
Wisdom Teeth Variation: - Student Experience: An orthodontist informed a student they have no bottom wisdom teeth. - Explanation: There is significant genetic variation. Some people grow all $4$ wisdom teeth, some grow only $2$ , and some grow none at all. - Removal: Wisdom teeth are often "chiseled out" around the age of $20$ if they interfere with other teeth.

Genetic Variation: Bullet point number $2$ of Darwin's Theory of Evolution is genetic variation, which explains why individuals within a species differ.
Inheritance: Traits are not passed on simply; they result from the shuffling of genetics from two partners. Each parent passes only one set of genes to the offspring.
Diversity in Offspring: There are approximately $76,000,000,000,000$ ( $76 \times 10^{12}$ ) different possible genetic combinations for children produced by the same two partners.

Snakes: - Snakes evolved from the lizard branch of reptiles and subsequently lost their legs. - Many snake species still develop "limb buds" ( $l-i-m-b$ buds) on their underside near the tail—beginnings of legs that never fully progress.
Flightless Birds: - Many bird species possess wings that are non-functional for flight. - Penguins: These birds possess wings that lost the original function of aerial flight but evolved a new function for "flying" underwater. - Ostriches: Possess wings that do not serve for flight or swimming.
Naked Mole Rat (Heterosophilus glitter): - This species lives $100\%$ of its life underground. - They possess vestigial eyes; they start to grow eyes during development, but the process is never completed. - They have non-functional balls of tissue in the front of their skulls instead of functional eyes and lack eyelids (the skin is smooth and closed). - They have lost most of their body hair but retain whiskers for sensing surroundings. - They navigate via touch (whiskers), vibrations through the ground, smell, and hearing.

Embryology Defined: The study of how organisms develop.
Developmental Similarity: This field shows that different species go through very similar developmental stages in the womb or egg.
Vertebrates: A group of animals characterized by having internal skeletons. - Includes: Mammals (human, dogs, etc.), reptiles, birds, amphibians, and fish.
Non-Vertebrates: Animals without internal skeletons, such as insects, arachnids, and shellfish.