Question

Scientist often talk about the evidence for evolution. Using the five types of evidence listed here, explain how each suggest the occurrence of evolution: 1) structural homologies, 2) molecular homologies, 3) developmental homologies, 4) fossils (general) and 5) transition fossils.

Answer 1

Evolution may be defined as any net directional change or any cumulative change in the characteristics of organisms or populations over many generations in other words, descent with modification.

It explicitly includes the origin as well as the spread of alleles, variants, trait values or character states.

1. Structural homologies.

If two or more species share a unique physical feature, such as a complex bone structure or a body plan, they may all have inherited feature from a common ancestor.

Physical features shared due to evolutionary history (a common ancestor) are said to be homologous.

example - The forelimbs of whales, humans, birds, and dogs look pretty different on the outside because they're adapted to function in different environments.

Bone structure of the forelimbs pattern of bones is very similar across species.

It's unlikely that such similar structures would have evolved independently in each species and more likely that the basic layout of bones was already present in a common ancestor of whales, humans, dogs, and birds.

2. Molecular homologies.

Different species share genetic homologies as well as anatomical ones.

Roundworms for example share 25% of their genes with humans.

These genes are slightly different in each species, but their striking similarites reveal their common ancestry.

The DNA code itself is a homology that links all life on Earth to a common ancestor.

DNA and RNA possess a simple four-base code that provides the recipe for all living things.

The transfer of genetic material from the cell of one living thing to the cell of another, the recipient would follow the new instructions as if they were its own.

3. Developmental homologies.

Embryological development of living things provides clues to the evolution of present-day organisms.

During the stages of development organisms exhibit ancestral features in whole or incomplete form.

Some species of living snakes have hind limb-buds as early embryos but rapidly lose the buds and develop into legless adults.

Developmental stages of snakes combined with fossil evidence of snakes with hind limbs supports the hypothesis that snakes evolved from a limbed ancestor.

4. Fossils.

Fossil remains of many thousands of organisms that lived in the past.

The fossil record shows that many kinds of extinct organisms were very different in form from any now living.

It also shows successions of organisms through time.

When an organism dies usually destroyed by other forms of life and by weathering processes.

On rare occasions some body parts particularly hard ones such as shells, teeth, or bones are preserved by being buried in mud or protected in some other way from predators and weather.

Eventually, they may become petrified and preserved indefinitely with the rocks in which they are embedded.

5. Transition fossil.

Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms.

Pakicetus is described as an early ancestor to modern whales. Although pakicetids were land mammals.

It is clear that they are related to whales and dolphins based on a number of specializations of the ear, relating to hearing.

A skull of the gray whale that roams the seas today has its nostrils placed at the top of its skull.

It would appear from these two specimens that the position of the nostril has changed over time and thus expected intermediate forms.