Mechanisms of Microevolution Natural Selection and Sexual Selection

Mechanisms of Microevolution Natural Selection and Sexual Selection

Natural Selection Natural selection is the process by which individuals with favorable traits that make them better suited for their environment are more likely to survive and reproduce.

Darwin’s 5 points About Natural Selection Conditions 1. Populations have genetic variations between individuals. 2. Some genetic variations are favorable for survival in certain situations. 3. More offspring are produced than can survive. 4. The offspring that survive have favorable traits for survival. 5. The genetic variability of a population will change over time. Memorize these key concepts!!

Directional Selection In directional selection one extreme of the phenotype is favoured resulting in a shift in the phenotype distribution. Why is larger body size favoured in horse evolution?

Stabilizing Selection In stabilizing selection the middle phenotype is favoured and extreme phenotypes are rarer. For example, why has human birth weight stabilized around 3 -4 kg? Small babies are less likely to survive and large babies can’t be born safely.

Disruptive Selection In disruptive selection the extremes of the phenotype are favourable for survival. This results in the loss of the intermediate phenotype. What happened to the intermediate phenotype of swallowtail moth? Why?

Sexual Selection Sexual selection is a very different set of processes. The evolutionary trend is for females to have large ova with lots of stored energy for zygote growth. The males have immense numbers of small mobile sperm. This had led to a huge variety of sexual behaviours and attractants.

Sexual Selection Is the male or female Siamese fighting fish more likely to get eaten? Why should males put so much energy into bright colours if it threatens individual survival?

Sexual Selection Sexual dimorphism is a strategy where one sex displays different physical characteristics to show fitness for mating. Most often the male is brightly coloured to show his fitness. Here the female Superb Bird of Paradise (Lophorina superba)is deciding, is he bright enough?

Sexual Selection Thus sexual selection usually involves a. competition between males b. mate choice by females This leads to enhanced reproductive success. Here a female Red Bird of Paradise (Paradisaea rubra) decides if the male’s courtship display is sufficient.

Artificial Selection • Artificial selection is when we, humans, act as the “environmental pressure” that shapes populations. • An example is dog breeding • All belong to the same species, Canis domesticus.

Artificial Selection: Dog Breeding • The originator of today’s domestic dog was an ancestral, wolf-like canid. By selecting for certain traits, we have created a variety of dogs that differ widely in appearance and temperament.

Artificial Selection: Crop Breeding

Genetic Fitness • Fitness is the quantitative representation of naturual and sexual selection within evolutionary biology. It describes individual reproductive success. • It is equal to the average contribution to the gene pool of the next generation that is made by individuals of the specified genotype or phenotype.

Video Tale of the peacock http: //www. youtube. com/watch? v=g. Kyb. Ap-n 7 M