Question

a. Explain the statement “When environmental conditions reverse, so does the selection pressure”. b. Describe two examples of artificial selection in detail. c. How do the fossils help us study evolution? Give two examples.

Answer 1

a. Migration and colonization of new habitats of humans lead to sharp changes in environmental conditions experienced by individuals. Humans confronted changes in the environmental conditions can lead to shifts in selective pressures on genomic regions associated with adaptation to pathogens and with phenotypes associated to metabolic syndrome. Therefore when environmental conditions reverse, so does the selection pressure. Thus new mutations may be advantageous or deleterious. An example of such case is the prevalence of metabolic syndrome such as type 2 diabetes and obesity, which has increased dramatically especially in industrialized countries in recent years. A hypothesis called Thrifty Genotype Hypothesis which supports to the high incidence of metabolic syndrome. This hypothesis states that alleles had a selective advantage in past environments became deleterious in the modern world due to external stimuli including dietary, climatic and behavioral changes. Another hypothesis which is alternative to this hypothesis is the Drifty Gene Hypothesis, which states that early hominins were subject to predation risks that selected against mutations associated with increased weigh. The more recent Homo species are released by the evolution of social behavior, discovery of fire and use of weapons. Such selective pressure allows metabolic disease genes to evolve under neutrality.

b.

Artificial selection is an ancient method of genetic engineering. It is the intentional breeding of domesticated animals, such as dogs, pigeons or cattle. Artificial selection has long been used in agriculture industry to produce animals and crops with desirable traits. The meats sold today are the result of the selective breeding of chickens, cattle, sheep, and pigs.

Example 1: Dog breeding is a prime example of artificial selection. All dogs are descendants of the wolf. For centuries, dogs have been bred for various desired characteristics, which lead to the creation of a wide range of dogs, from the tiny Chihuahua to the massive Great Dane. By the use of artificial selection humans drastically alter the appearance of dogs.

Example 2: Through artificial selection many fruits and vegetables have been improved or even created. For example, broccoli, cauliflower, and cabbage were all derived from the wild mustard plant through selective breeding. Artificial selection appeals to humans since it is faster than natural selection and allows humans to mold organisms to their needs.

c. Fossils are the traces or preserved remains of plants and animals from the past. Fossils range in age from 10,000 to 3.48 billion years old. Fossils provide solid evidence that organisms from the past are not the same as those found today. Fossils show a progression of evolution. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological or anatomical record. By comparing both anatomies paleontologists can infer the lineages of both modern and extinct species. This approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Fossils help paleontologists them learn about when and how different species lived millions of years ago.