AP BIO: SUMMER WORK: ASSIGNMENT 2

Anatomy

The study of the structure of the body and its parts including bones and organs and how they fit together

Vertebrate

An animal with a backbone

Embryo

An organism in its earliest stage of development

Digits

The technical term for fingers and toes

Tetrapod

A four-limbed vertebrate meaning the group of land vertebrates that descended from fish

Transitional fossil

A fossil showing a mix of features from two different groups which captures an evolutionary shift in progress

Polydactyly

A condition in which an individual is born with extra fingers or toes

Neil Shubin

The paleontologist who predicted and discovered Tiktaalik and argues that the human body is a modified fish body

Sir Richard Owen

The scientist who discovered that all limbed animals share the same internal bone pattern which he called the archetype

Owen's limb pattern

One bone then two bones then many small bones then digits which is found in every limbed animal from a human arm to a bat wing to a whale flipper

Why Owen mattered

He documented the shared limb pattern before Darwin but could not explain it and Darwin later supplied the reason which is inheritance from a common ancestor

Jenny Clack and Stephanie Pierce

Researchers who studied the early tetrapod Ichthyostega using fossils and CT scans to learn how the first limbed vertebrates moved and whether they could truly walk on land

Ichthyostega

One of the earliest four-legged vertebrates whose limited movement resembled a seal hauling itself forward more than a true four-legged walk

Cliff Tabin

The researcher who investigated the genes that control limb development in embryos

Sonic hedgehog

A gene that patterns the developing limb by determining where digits form and which side becomes the thumb

Fruit flies in evolution research

The organism where scientists first found master body-building genes after mutations produced legs growing where antennae should be

Genetic toolkit

The set of ancient body-building genes shared by nearly all animals including humans which is why discoveries in fruit flies apply to human development

Kamani's six fingers

A case of polydactyly caused by a mutation that changed where and how much Sonic hedgehog was active during limb development which shows that small changes in gene activity change anatomy

Tiktaalik

A 375 million year old transitional fossil nicknamed a fishapod because it combines fish features with land-animal features

Tiktaalik fish traits

Scales and gills and fins

Tiktaalik land-animal traits

A flat head with eyes on top and a neck that lets it move its head independently of its body and lungs and fins containing shoulder and elbow and wrist bones strong enough to prop the body up

Why Tiktaalik has a neck

No fish can move its head independently of its body so a neck is a land-animal feature and one of the clearest signs that Tiktaalik is transitional

Shubin's prediction

Fish fossils are about 385 million years old and land vertebrates about 365 million so the in-between animal should be in rock about 375 million years old from an ancient freshwater environment and exposed at the surface

Ellesmere Island today

A frozen and barren treeless polar desert in the Canadian Arctic that is bitterly cold and windy and remote with polar bears

Ellesmere Island 375 million years ago

Located near the equator and warm and subtropical with shallow streams and rivers and floodplains full of lush plant life much like the Amazon today

Why Shubin searched the Arctic

Not because it is cold but because rock of the right age from the right ancient shallow-water environment happens to be exposed at the surface there

Progression of vertebrate evolution

Fish then amphibians then reptiles then mammals then primates then humans with each group inheriting and modifying the body plan of the group before it

Opposable thumb

The primate hand feature that allows the thumb to rotate and touch the other fingers which enables gripping objects and manipulating tools with precision

Why fish anatomy teaches us about human anatomy

Humans and fish share a common ancestor and the basic blueprint of the human body first evolved in fish so through descent with modification those structures were inherited and remodeled for life on land

Fish and human embryos

Early in development they look strikingly similar and share arches in the neck region that become gills in fish but become parts of the jaw and ears and throat in humans

Why embryos are useful evidence

The same genes build bodies in fish and humans so development replays the evidence of common ancestry and shows where our structures came from

Fins to weight-bearing limbs

In water the water holds the animal up but on land gravity must be resisted so fins had to become limbs strong enough to bear weight

Three kinds of evidence in the film

Bones showing the shared limb pattern and fossils showing transitional forms like Tiktaalik and genes showing that the same developmental toolkit builds fins and hands

Central argument of Your Inner Fish

The human body is a modified fish body because every major structure was inherited from aquatic ancestors and repurposed for life on land