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Biology and Chemistry

Snakes of the Southeast U.S. Fossil Hominids, Human Evolution: Thomas Huxley & Eugene Dubois. Fossil Hominids, Human Evolution: Thomas Huxley & Eugene Dubois When Charles Darwin wrote the Origin of Species, he had to wonder about how humans came to be.

Fossil Hominids, Human Evolution: Thomas Huxley & Eugene Dubois

Humans had hereditary variation in every generation, and some individuals had more children than others — the key ingredients for natural selection. But he chose not to write about humans in his first book about evolution, in large part out of strategy. In 1857, two years before Darwin published the Origin of Species, Wallace asked him in a letter if he would discuss the origin of mankind in the book.

Darwin replied, "I think I shall avoid the whole subject, as so surrounded with prejudices, though I fully admit that it is the highest and most interesting problem for the naturalist. " But Darwin also knew that he had no fossil record to use to develop a hypothesis about human evolution. Shortly after Darwin published the Origin of Species, his great champion Thomas Huxley (right) considered the skull from the Neander valley. What is Half-life? - What is the Definition of Half-life?

Gcsescience.com 16 gcsescience.com Radioactivity Half-life.

What is Half-life? - What is the Definition of Half-life?

What is Half-life? 1. Half-life is the time taken for half of the radioactive nuclei to decay. 2. There are a number of ways to define half-life.

Nucleic

Amino Acids. Introduction Essential amino acids Why learn this?

Amino Acids

Amino acids play central roles both as building blocks of proteins and as intermediates in metabolism. The 20 amino acids that are found within proteins convey a vast array of chemical versatility. The precise amino acid content, and the sequence of those amino acids, of a specific protein, is determined by the sequence of the bases in the gene that encodes that protein. The chemical properties of the amino acids of proteins determine the biological activity of the protein.

Proteins not only catalyze all (or most) of the reactions in living cells, they control virtually all cellular process. As we learn about amino acids, it is important to keep in mind that one of the more important reasons to understand amino acid structure and properties is to be able to understand protein structure and properties. Top Essential amino acids Humans can produce 10 of the 20 amino acids.

Why learn these structures and properties? Human Biological Adaptability: Skin Color as an Adaptation. Skin color is due primarily to the presence of a pigment called melanin , which is controlled by at least 6 genes.

Human Biological Adaptability: Skin Color as an Adaptation

Both light and dark complexioned people have melanin. However, two forms are produced--pheomelanin , which is red to yellow in color, and eumelanin , which is dark brown to black. People with light complexioned skin mostly produce pheomelanin, while those with dark colored skin mostly produce eumelanin. In addition, individuals differ in the number and size of melanin particles. The latter two variables are more important in determining skin color than the percentages of the different kinds of melanin. Nature has selected for people with darker skin in tropical latitudes, especially in nonforested regions, where ultraviolet radiation from the sun is usually the most intense. Such a non-random distribution pattern of human skin color was predicted by Constantin Wilhelm Lambert Gloger, a 19th century German zoologist. GetSharedSiteSession?rc=4&redirect= Figure 1 (a) Alignment of AT-rich interaction domain (ARID) proteins over the core ARID, generated using the MAP multiple-sequence alignment program.

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Invariant and conserved residues are indicated by a red or dark-green background, respectively. Similar residues are indicated by a yellow background. Residues are considered similar for this purpose if they fall into one of the following groups: F,Y,W; I,L,V,M; R,K; D,E; S,T; Q,N; or G,A. Hydrophobic Interactions. Dog Breeds - Browse nearly 350 different breeds - Next Day Pets. Get Notified Get Notified When New Puppies Are AddedReceive an email alert when additional puppies are added.

Dog Breeds - Browse nearly 350 different breeds - Next Day Pets

It's easy and free! Choosing dog breeds based on your lifestyle is the most important factor when adopting a puppy. View our complete dog breed profiles to get a better understanding of expected temperament, character, care and exercise requirements. We recommend our BreedMatch tool to help narrow down your favorite dog breeds. BREED GROUP: ToyWEIGHT: 7-9 lbsHEIGHT: 9-11.5 inchesCOLOR(S) black, gray, silver, or black and tan Size: Grooming Needs: Exercise Needs: Good With Dogs: Watchdog Ability: BREED GROUP: HoundWEIGHT: Male: 60; Female: 50 lbsHEIGHT: Male: 27; Female: 25 inchesCOLOR(S) all colors permissible except spotted BREED GROUP: TerrierWEIGHT: 45 lbsHEIGHT: 23 inchesCOLOR(S) tan with black or grizzle saddle.