2037 Astro Spring 07, Lecture 05
Common Character of Life
Order Reproduction Growth and development Energy utilization Response to the environment Evolutionary adaptation
Evolution as Biology's Unifying Theme, proposed by Charles Darwin in his book The Origins of Species in 1858 An evolutionary biologist Stephen Jay Gould summarized Darwin's theory as "two undeniable facts and an inescapable conclusion" Fact 1: overproduction and struggle for survival Fact 2: Individual variations The inescapable conclusion: unequal reproductive success, i.e. Natural Selection Over time, advantageous genetic traits will naturally win out over less advantageous traits
Natural selection is the primary mechanism of evolution Example: An evolutionary sequence on how an imaginary population of beetles of mixed color evolves into dark beetles A group of beetles with different color A hungry bird can easily see the beetles that are lighter color
Generation after generation, the beetle population adapts to its black environment to have dark color
An Evolutionary Tree for the 13 Species of Galapagos Finches Darwin discovered that the species on these young volcanic islands closely resemble one another and mainland finches However, each species is adapted to particular microenvironments and lifestyle!
Why did Darwin choose these volcanic islands?
Location of Galapagos Islands: Around the equator belong to Ecuador Country
Galapagos
Volcano activities indicate the islands are relatively young, possible contamination from other factors are small.
The Other Strong Support Darwin Found Is Artificial Selection: the Selective Breeding of Domesticated Plants and Animals by Humans
The six vegetables all look and taste quite different, but they were all bred by humans from the same wild ancestor (wild mustard). Thus they all have one common ancestor, yet they look very different.
Can you imagine big Rottweilers share the same ancestors as Chihuahuas?
A Rottweiler as big as a human
A Chihuahua as small as a cat
Artificial selection can cause such profound changes in just a few thousands years. Can you image what the natural selection could do to life on Earth over millions or billions of years?
Human beings originated in Africa and spread out to the entire world in ~70,000 years
On Earth, natural selection occurs in our environment as fast as a decade or even shorter. In fact, human beings are not the only ones who evolve very fast. Think about on a microbial level, natural selection allows a population of bacteria to become resistant to specific antibiotics. Pharmaceutical companies have to develop new antibiotics very fast bacteria as become resistant to existing ones. Modern biology provides a good answer about evolution and natural selection on a molecular level DNA (deoxyribonucleic acid), instructing organism building, passing hereditary traits from one generation to the next
DNA Replication: DNA copies itself by "unzipping" its two strands, each serves as a template for making a new complimentary strand in accord with the base pairing rules Four chemical bases (A, T, C and G), rules: A goes only with T, C only with G The entire human genome would add up to about 60,000 separate genes carrying about 3 billion base pairs
In sexual reproduction, each fertilization creates a cell that receives half of its chromosomes (that carries DNA) from each parent
Due to the gene mix from both parents, a great variety of gene combinations can occur, some of the new generations which better fit the environment will survive
A definition of life: Life is something that can reproduce and evolve through natural selection (although some cases may still challenge this definition)
Because of gene adaptability for different environments, life can possibly survive in some extreme conditions
A volcanic vent on the ocean floor spewing out extremely hot (400 C), mineral-rich water A hot spring in Yellowstone National Park
Scientists have found life in water with temperatures above 110C (230 F)
The different colors in the water are from different microbes that survive in water of different temperatures
A dry and extremely cold valley in Antarctica also hosts life The ice comes from runoff from surrou...