Reviewing Key Concepts Evidence for Evolution Mastering Biology

Learning Objectives

Past the end of this section, yous will be able to:

• Explain sources of bear witness for development
• Ascertain homologous and vestigial structures

The evidence for evolution is compelling and extensive. Looking at every level of organization in living systems, biologists meet the signature of by and present evolution. Darwin dedicated a large portion of his book, On the Origin of Species, identifying patterns in nature that were consistent with evolution and since Darwin our agreement has become clearer and broader.

Fossils

Fossils provide solid evidence that organisms from the past are not the aforementioned as those found today; fossils show the gradual evolutionary changes over time. Scientists determine the historic period of fossils and categorize them all over the world to make up one's mind when the organisms lived relative to each other. The resulting fossil record tells the story of the past, and shows the evolution of grade over millions of years (Figure eleven.x). For example, highly detailed fossil records have been recovered for sequences of species in the evolution of whales and mod horses. The fossil record of horses in Due north America is particularly rich and many contain transition fossils: those showing intermediate anatomy between earlier and later forms. The fossil record extends back to a domestic dog-like ancestor some 55 million years ago that gave rise to the outset equus caballus-like species 55 to 42 one thousand thousand years agone in the genus Eohippus. The series of fossils tracks the change in anatomy resulting from a gradual drying trend that changed the mural from a forested one to a prairie. Successive fossils show the evolution of teeth shapes and foot and leg anatomy to a grazing habit, with adaptations for escaping predators, for example in species of Mesohippus found from 40 to 30 million years ago. Later species showed gains in size, such as those of Hipparion, which existed from about 23 to 2 million years ago. The fossil record shows several adaptive radiation in the horse lineage, which is at present much reduced to only i genus, Equus, with several species.

Figure 11.10 This illustration shows an creative person'due south renderings of these species derived from fossils of the evolutionary history of the horse and its ancestors. The species depicted are just four from a very various lineage that contains many branches, expressionless ends, and adaptive radiations. 1 of the trends, depicted here is the evolutionary tracking of a drying climate and increase in prairie versus forest habitat reflected in forms that are more adapted to grazing and predator escape through running. Przewalski'due south horse is i of a few living species of equus caballus.

Beefcake and Embryology

Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For case, the bones in the appendages of a homo, domestic dog, bird, and whale all share the same overall construction (Effigy 11.eleven). That similarity results from their origin in the appendages of a mutual antecedent. Over time, evolution led to changes in the shapes and sizes of these basic in different species, merely they take maintained the same overall layout, evidence of descent from a common ancestor. Scientists call these synonymous parts homologous structures. Some structures exist in organisms that have no credible function at all, and appear to be residual parts from a past ancestor. For case, some snakes have pelvic bones despite having no legs because they descended from reptiles that did take legs. These unused structures without function are called vestigial structures. Other examples of vestigial structures are wings on flightless birds (which may have other functions), leaves on some cacti, traces of pelvic bones in whales, and the sightless eyes of cavern animals.

Figure 11.11 The similar construction of these appendages indicates that these organisms share a common antecedent.

Link to Learning

Concept in Action

Click through the activities at this interactive site to guess which bone structures are homologous and which are analogous, and to see examples of all kinds of evolutionary adaptations that illustrate these concepts.

Another evidence of development is the convergence of grade in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan (a bird), living in the chill region accept temporary white coverings during winter to blend with the snow and ice (Effigy 11.12). The similarity occurs not because of common ancestry, indeed one covering is of fur and the other of feathers, but because of similar selection pressures—the benefits of not beingness seen by predators.

Figure 11.12 The white winter coat of (a) the arctic fox and (b) the ptarmigan'south plumage are adaptations to their environments. (credit a: modification of piece of work by Keith Morehouse)

Embryology, the study of the development of the anatomy of an organism to its adult form as well provides evidence of relatedness between now widely divergent groups of organisms. Structures that are absent in some groups often appear in their embryonic forms and disappear by the time the adult or juvenile grade is reached. For instance, all vertebrate embryos, including humans, showroom gill slits at some signal in their early on development. These disappear in the adults of terrestrial groups, but are maintained in adult forms of aquatic groups such as fish and some amphibians. Peachy ape embryos, including humans, have a tail construction during their development that is lost by the time of birth. The reason embryos of unrelated species are often similar is that mutational changes that bear upon the organism during embryonic evolution can crusade amplified differences in the developed, even while the embryonic similarities are preserved.

Biogeography

The geographic distribution of organisms on the planet follows patterns that are best explained by development in conjunction with the movement of tectonic plates over geological time. Broad groups that evolved earlier the breakdown of the supercontinent Pangaea (about 200 meg years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, for instance the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of Proteaceae in Commonwealth of australia, southern Africa, and South America is best explained by the plant family's presence there prior to the southern supercontinent Gondwana breaking up (Figure xi.13).

Figure eleven.13 The Proteacea family of plants evolved earlier the supercontinent Gondwana broke up. Today, members of this institute family are institute throughout the southern hemisphere (shown in red). (credit "Proteacea bloom": modification of work by "dorofofoto"/Flickr)

The groovy diversification of the marsupials in Australia and the absenteeism of other mammals reflects that island continent's long isolation. Australia has an abundance of endemic species—species found nowhere else—which is typical of islands whose isolation past expanses of water prevents migration of species to other regions. Over time, these species diverge evolutionarily into new species that wait very different from their ancestors that may exist on the mainland. The marsupials of Australia, the finches on the Galápagos, and many species on the Hawaiian Islands are all found nowhere else merely on their island, yet display afar relationships to ancestral species on mainlands.

Molecular Biology

Similar anatomical structures, the structures of the molecules of life reverberate descent with modification. Testify of a common ancestor for all of life is reflected in the universality of DNA as the genetic cloth and of the virtually universality of the genetic code and the machinery of DNA replication and expression. Fundamental divisions in life between the three domains are reflected in major structural differences in otherwise conservative structures such as the components of ribosomes and the structures of membranes. In general, the relatedness of groups of organisms is reflected in the similarity of their Deoxyribonucleic acid sequences—exactly the design that would exist expected from descent and diversification from a common ancestor.

Deoxyribonucleic acid sequences accept also shed low-cal on some of the mechanisms of evolution. For example, information technology is clear that the evolution of new functions for proteins normally occurs later on gene duplication events. These duplications are a kind of mutation in which an entire gene is added as an extra copy (or many copies) in the genome. These duplications allow the complimentary modification of one copy past mutation, option, and drift, while the second copy continues to produce a functional protein. This allows the original function for the protein to be kept, while evolutionary forces tweak the copy until it functions in a new way.

vegawive1983.blogspot.com

Source: https://openstax.org/books/concepts-biology/pages/11-3-evidence-of-evolution

Share this post