Home Forums Hunting & Shooting Hunter's Campfire Evolution Scientifically Debunked

I'd suggest that you actually study the subject using reliable academic textbooks or websites on biology and evolution rather than creationist sources and their misleading videos.

Mutations happen, many if not most are not beneficial, but some are. If a mutation happens to be beneficial or adaptive, it gets past on. Which in turn alters the genetic makeup of the group to a degree, a change. Accrue enough changes, that group becomes a new species.


DNA Basics

''In one respect the basic structure of DNA resembles that of proteins: both are made of linear chains of varying subunits. Apart from this common feature, DNA structure is quite different from that of proteins. The subunits in DNA are called nucleotides or bases, and the sequence of these nucleotides contains the genetic information specifying the sequence of amino acids in each protein made by the organism. Whereas 20 different amino acids comprise the subunits of proteins, there are only four different nucleotide bases in DNA, generally abbreviated A, T, G and C. According to the "genetic code" deduced by scientists in the 1960s, each amino acid is specified by one or more triplets of nucleotides; for example, the sequence GCG specifies the amino acid alanine. Since there are 64 different triplets (each called a codon) and only 20 amino acids to specify, some amino acids are represented by more than one triplet (e.g. ATA, ATC and ATT all code for the amino acid isoleucine); and three triplets -- TAA, TAG and TGA -- represent "stop codons" that mark the end of the gene sequence that can be used to specify amino acid sequence.


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Figure 1. DNA Basics. The central oval represents a cell, within which lies the nucleus. Inside the nucleus, most of the DNA exists as a double helix. The oval at upper left shows an expanded view of the DNA, in which the helices have been drawn "untwisted" to reveal similarity to a ladder. The genetic information is stored in the sequences of nucleotide bases (A, T, G or C) that form the rungs of the ladder. Each rung is formed by a pair of nucleotide bases touching each other, one base attached to one strand backbone, and the other attached to the other strand backbone. An "A" nucleotide always pairs with a "T," and a "G" always pairs with a "C." In order to synthesize a protein, the cell reads the genetic information of the gene for that protein by "transcribing" a molecule of RNA from the gene. For transcription, the strands of the DNA double helix must partially separate so that the bases that form RNA can assemble according to the rules of complementary basepairing. The expanded view at upper right shows the two major differences between RNA and DNA: the RNA backbone strand has a slightly different chemical structure (represented by the dashed line), and a slightly modified form of "T" known as "U" is found in RNA. The transcribed strand of RNA acts as a "messenger" that carries the genetic information from storage in the nucleus to the protein manufacturing modules (represented in the figure by double grey ovals) in the cytoplasm. The expanded view at lower left shows that the sequence of RNA bases is read so that each triplet of bases specifies an amino acid (aa1, aa2, etc.) in the protein. The protein folds into a functional three-dimensional structure that depends on the linear sequence of amino acids.

DNA contains two linear chains in a double-stranded structure that resembles a twisted ladder--the famous "double helix." The vertical beams of the ladder represent a uniform backbone chain which contains no sequence information. As shown in Figure 1 above, the information is stored in the "rungs" of the ladder, which are formed from a pair of nucleotide bases, each sticking out from one vertical backbone strand and touching the base from the opposite strand to form a "rung." The base G on one strand always contacts a base C on the opposite strand; similarly an A always contacts a T. Thus a string of Ts on one strand can "basepair" or "anneal" with a strand containing a string of As to form a double-stranded structure. The sequence of nucleotide bases in one strand is said to be "complementary" to the sequence of the other strand. For any one gene the triplets of bases encoding amino acid sequence are on only one strand. Some genes are encoded on one strand, while other genes lie on the other strand. In most mammalian genes the DNA coding for amino acid sequences is interrupted by segments of apparently meaningless DNA ("introns"). Intron sequences need to be removed before the sequence is used to assemble amino acids; this removal, or splicing, does not occur in the DNA molecule, but in the next stage of information transfer.

In order for a cell to produce a particular protein whose amino acid sequence is encoded in a gene, the sequence information in the DNA must first be copied or "transcribed" into a single-stranded molecule called ribonucleic acid (RNA), as shown above in Figure 1. This initial transcript of RNA undergoes several structural alterations, known collectively as "processing," before it is used to assemble amino acids. These processing steps include the "splicing" out of unnecessary intron segments from the RNA and the addition of nucleotides at one end--the "poly(A) tail"--which promote proper functioning of the RNA in the cell. It is the "processed" RNA that participates directly in the assembly of amino acids into proteins. The transcription of a gene into an RNA copy is very tightly controlled, in part by highly specific regulatory sequences known as promoters that for most genes occur in the DNA just outside the transcribed region but close to the position where the transcription into RNA should start.

When a cell divides, the entire sequence of its DNA must be duplicated into two faithful copies of the original; one copy goes to each of the "daughter" cells created by the division. Occasionally, errors occur in this copying mechanism, creating "mutations" in the DNA sequence. There are several types of mutations, including substitutions of one or a few nucleotides, deletions of nucleotides, duplication of segments of DNA or insertion of extraneous DNA segments into an unrelated DNA sequence. Such changes can occur in most cells in the body--liver, skin, muscle, etc.--without being transmitted to offspring when the organism reproduces. However, when mutations occur in the egg or sperm or, more generally in "germline cells" (i.e., the egg or sperm plus their embryological precursors), they can be passed on to future generations. Often, mutations are inconsequential: e.g. they may fall outside a gene, or if within a gene they may not change the amino acid encoded. Many genetic differences between closely related species are thought to represent such random inconsequential mutations. Sometimes, however, mutations critically damage the function of a gene. Indeed, such mutations are the cause of genetic diseases like cystic fibrosis, sickle cell anemia, phenylketonuria, and hundreds of others, as well as many genetic aberrations studied in laboratory animals. When molecular geneticists examine the DNA of patients with such well-characterized diseases, they can almost always find the defective gene and identify the mutation that inactivated it, since it is rare for such genetic disease to be caused by a deletion that removes an entire gene. Mutations causing genetic diseases and malformations are generally so detrimental to the organism's survival and reproductive success that in the wild--i.e. in the absence of modern medical science--they would tend to be "weeded out" by the pressure of natural selection. Rarely, mutations can be beneficial to an organism: these rare cases form the basis for evolutionary adaptations that improve the "fitness" of an organism to its environment.''