Question

1. Trace our hominid ancestor tree (pick 5 ancestors) and include rough dates. What hominids are most closely related to us? When humans left Africa, what areas were colonized last?

2. How could genetic drift counteract natural selection? Be sure to give a real-world example.

3. What are the key components for natural selection? Give an example of each.

4. What are the major branch points for plant evolution?

5. What are the major branch points for animal evolution?

6. What are some of the major ways that the percentage of alleles in a population could change? Explain whether the process increases or decreases the variety of alleles.

Answer 1

A. Homo sapiens: 2,00,000 years ago.

Homo neander: 7,00,000 to 3,00,000 years ago.

Homo heidelberg: 3,50,000 and 4,00,000 years ago.

Homo erectus: 2 million years ago.

Homo habilis: 2.4 to 1.5 million years ago.

Chimpanzees are the most closest living relatives of Humans. After leaving Africa, the last place to be colonized by the humans were the Americas via Alaska, Northeast Asia and the Bering Sea Land bridge.

B. Genetic drift id defined as the change in the frequency of an existing gene variant in a population due to random sampling of organisms. Natural selection is defined as the differential survival and reproduction of individuals due to differences in phenotype and it is a key mechanism of evolution. genetic drift has been said to counteract natural selection as many slightly beneficial mutations can be lost by chance and many deleterious mutations can spread and become fixed in a population. Genetic drift is largest in a small population as it may lead to large changes in populations over a short period of time. For example: a population of rabbit can have both brown and white fur where brown fur color is the dominant allele. Due to genetic drift by random chance, the offspirng may all have brown fur which may reduce or eliminate the allele for white fur color.

C. Natural selection is a process whereby organisms better adapted to their environment tend to survive and produce more offspring. The four conditions or components that are needed for natural selection to occur are: variation, heredity, high rate of population growth and differential survival and reproduction.

Variation: Organisms within a given population exhibit individual variations in appearance and behavior such as body size, hair color, facial markings, voice properties or number of offsprings. Example: Within the same population some lizards developed longer leg bones to help them cllimb up during periods of flood and to escape predators in the ground; while some lizards have shorter legs that provide no advantage during flood and predation. As a result, the lizards with shorter leg died out and only lizards with long legs survived.

Heredity: Some traits are inherited from parents by offspring while some traists are strongly influenced by environmental conditions and show weak heritability. Bacteria that were initially unstable in new environment with new food resources have adapted well to their new environment. They have adapted to the presence of deadly antibiotics and survided. This trait is passed on to their offspring that are also resistant to the antibiotic.

High rate of population growth: Most populations have high rate of reproduction than the resources available which lead to struggle for resources. Each generation experiences substantial mortality. Example: Bacteria can generate several generations in one day and can adapt to their new environment.

Differential survival and reproduction: Individuals possessing traits well suited for the struggle for local resources will contribute more offsprings to the next generation. Example: Green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

D. Plant evolution is the subset of evolutionary phenomena that concerns plants. The major branch points for plant evolution are origin of plants from algae, evolution of vascular tissues, evolution of seeds and evolution of flowers.

E. During evolution of animals four major branch pints have occured:

i] Eumetazoans seperate from Parazoans: Eumetazoans are animals with true tissues while Parazoans are animals without true tissue.

Bilateria separate from Radiata: Bilateria are bilaterally symmetrical whereas Radiata are radially symmetrical.

Coelomates separate from Acoelomates and Pseudocoelomates: Coelomates have body cavity within mesoderm. Pseudocoelomates have a body cavity between mesoderm and endoderm. Acoelomates have solid bodies with no body cavities.

Deuterostomes separate from Protostomes: In Deuterostomes the mouth is formed from the secondary opening and the blastopore forms the arse. In Protostomes the mouth develops from the blastopore and arse develops secondarily somewhere else.

F. Natural selection, genetic drift and gene flow are the mechanisms that cause changes in allele frequencies over time. Natural selection occurs when individuals with certain genotypes are more likely than individuals with other genotypes to survive and reproduce and thus to pass on their alleles to the next generation. Natural selection can only increase or decrease frequency of allels that already exist in the population. genetic drift results from the sampling error inherent in the transmission of gametes by individuals in a finite population. genetic drift decreases genetic diversity within a population. Gene flow is the movement of genes into or out of a population. such movement may be due to migration of individual organisms that reproduce in their new populations or to the movement of gametes. Gene flow within a population can increase the genetic variation of the population, whereas gene flow between genetically distant populations reduce the genetic difference between the populations.