Block1 Anatomy Physiology

What are the evidences for evolution from : Anatomy and Physiology By: Bentley Snider, Ellie Dickins, Ali Cipriani

The Field of Comparative Anatomy In the early 19 th century, a man named Baron Cuvier placed the field of comparative anatomy on a more scientific basis by asserting that animals' structural and functional characteristics result from their interaction with their environment. Darwin made extensive use of comparative anatomy in advancing his theory, and it in turn revolutionized the field by explaining the structural differences between species as arising out of their evolutionary descent by natural selection from a common ancestor. The fish, which lives in water, has gills through which it breathes. It has no lungs. The frog, which lives on land as well as in water, is equipped with lungs for air breathing. The earthworm has neither lungs nor gills. It breathes through its skin.

comparative-anatomy the comparative study of the body structures of different species of animals in order to understand the adaptive changes they have undergone in the course of evolution from common ancestors. Since Darwin's time, the study of comparative anatomy has centered largely on body structures that are homologous (ones in different species that have the same evolutionary origin regardless of their present-day function) Such structures may look quite different and perform different tasks, but they can still be traced back to a common structure in an animal that was ancestral to both. Analogous structures may resemble each other because they perform the same function, but they have different evolutionary origins and often a different structure.

Comparative anatomy, the other major subdivision of the field, compares similar body structures in different species of animals in order to understand the adaptive changes they have undergone in the course of evolution. The position and attachment of muscles change during evolution; a muscle lying in the same position and attached to the same bone or cartilage in one vertebrate may have different origins from those of another vertebrate species.

Many organisms possess vestigial structures that have no apparent function, but that resemble structures their presumed ancestors had. It is difficult to understand vestigial structures such as these as anything other than evolutionary relicts, holdovers from the evolutionary past. Comparisons of the anatomy of different living animals often reveal evidence of shared ancestry. In some instances, the same organ has evolved to carry out different functions, in others, an organ loses its function altogether. Sometimes, different organs evolve in similar ways when exposed to the same selective pressures.

Vestigial Structures

Definition : A structure that has diminished

in size and usefulness in the course of

evolution.

Examples: APPENDIX

The human appendix is part of the digestive system;

attached at the beginning of the

large intestine.

It serves absolutely NO purpose

in humans today, and people who

get their appendix removed

experience no physical effects.

Examples: WISDOM TEETH

It is believed that Wisdom teeth in humans used to be used to chew tough foods, etc.

They used to be much more massive than they are today.

Today, they serve no purpose and our usually removed.

Examples: GOOSE BUMPS

It is believed that back when humans had hair covering their body, the muscles at the base of our hairs would pull the hairs up, letting them stick out. This would keep humans warm.

As we have developed over time (with clothes, etc), we haven’t needed goose bumps so. We have gradually lost bushy body hair and therefore, the point of goose bumps.

Examples: VITAMIN C Most mammals (not humans) can produce Vitamin C within their bodies. It is believed that there was a point in time when the loss of Vitamin C was not a significant disadvantage. Therefore, the gene that produces Vitamin C was mutated to be inefficient.

Previous conception of similar animals

A scientist by the name of Geoffroy set out to disprove common conception

Example that gave Geoffroy the clue that there were many holes in the common conception

Vertebrate's skeletons vs. archetypal vertebra

Geoffroy said that, essentially,

all animals came from one

A bat, a manatee, and a bird can all be linked together

Bat:

Manatee:

Bird:

Each differentiate in function, according to the environment, however the structures are quite similar: All have fingers attached to hard wrist bones, tacked on to a pair of long bones which trace back to one bone.

Example of Geoffroy’s Idea

Darwin was attempting to prove the idea that Geoffroy brought to light. A friend of Darwin, Owen, encouraged Darwin to discover similarities of a barnacle and the typical crustacean archetype.

Darwin claimed that all animals had a basic layout of a spinal chord, ribs and a mouth, but different animals were formed by more complex layouts.

Darwin began a very

lengthy study over a

number of years over

studying different types

of barnacles and their

anatomy: how they

have changed over time.

After Darwin’s time, evolutionary researchers and scientists have enlarged the umbrella of evolution to include physiology, ecology, biochemistry and systematics.

Physiology: Study of the functioning of living organisms, animal or plant, and of the functioning of their constituent tissues or cells (def. taken from the ‘physiology MLA bibliog.)

Therefore, it is safe to say that scientists have found that over time, the functioning of the living organisms, animal or plant, and of the functioning of their constituent tissues or cells have evolved.

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