Energy, genes and evolution: introduction to an evolutionary synthesis published a fine paper on vectorial chemistry in relation to the origin of life in . The understanding of evolutionary biology began with the publication of To explain these relationships, Darwin said that all living things were related. Life is the harnessing of chemical energy in such a way that the energy- harnessing device makes a copy of itself. No energy, no evolution. The 'modern.
If all the individuals of a species reproduced successfully, the population of that species would increase uncontrollably. Populations tend to remain about the same size from year to year. Environmental resources are limited. No two individuals in a given species are exactly alike. Much of this variation in a population can be passed on to offspring. Darwin deduced that since organisms produce more offspring than their environment could possibly support, there must be a competitive struggle for survival - only a few individuals can survive out of each generation.
Darwin realized that it was not chance alone that determined survival. Instead, survival depends on the traits of each individual and if these traits aid or hinder survival and reproduction. Well-adapted, or "fit", individuals are likely to leave more offspring than their less well-adapted competitors. Darwin realized that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population.
Traits that help an organism survive and reproduce would accumulate over generations. On the other hand, traits that hinder survival and reproduction would disappear.
Darwin used the term "natural selection" to describe this process. For example, Darwin observed that orchids and insects have a close relationship that allows the pollination of the plants. In this way, insects transport the pollen from a male to a female orchid.
In spite of the elaborate appearance of orchids, these specialized parts are made from the same basic structures that make up other flowers. Darwin proposed that the orchid flowers did not represent the work of an ideal engineer, but were adapted from pre-existing parts, through natural selection. This led to an immediate joint publication of both theories.
The tips of the limbs represented modern species and the branches represented the common ancestors that are shared amongst many different species. To explain these relationships, Darwin said that all living things were related, and this meant that all life must be descended from a few forms, or even from a single common ancestor. He called this process "descent with modification".
His theory means that all life, including humanity, is a product of continuing natural processes. The implication that all life on earth has a common ancestor has met with objections from some religious groups who believe even today that the different types of life are due to special creation. However, he could not explain the source of these variations.
Like many of his predecessors, Darwin mistakenly thought that heritable traits were a product of use and disuse, and that features acquired during an organism's lifetime could be passed on to its offspring.
He looked for examples, such as large ground feeding birds getting stronger legs through exercise, and weaker wings from not flying until, like the ostrich, they could not fly at all.
In the late 19th century this theory became known as Lamarckism. Darwin produced an unsuccessful theory he called pangenesis to try to explain how acquired characteristics could be inherited. In the s August Weismann's experiments indicated that changes from use and disuse could not be inherited, and Lamarckism gradually fell from favor. This is like mixing different hands of cards, with an organism getting a random mix of half of the cards from one parent, and half of the cards from the other.
Mendel called the information factors; however, they later became known as genes. Genes are the basic units of heredity in living organisms. They contain the information that directs the physical development and behavior of organisms.
Genes are made of DNA, a long molecule that carries information. This information is encoded in the sequence of nucleotides in the DNA, just as the sequence of the letters in words carries information on a page. The genes are like short instructions built up of the "letters" of the DNA alphabet. Put together, the entire set of these genes gives enough information to serve as an "instruction manual" of how to build and run an organism.
The instructions spelled out by this DNA alphabet can be changed, however, by mutations, and this may alter the instructions carried within the genes. Within the cell, the genes are carried in chromosomes, which are packages for carrying the DNA, with the genes arranged along them like beads on a string. It is the reshuffling of the chromosomes that results in unique combinations of genes in offspring.
The end products of natural selection are organisms that are adapted to their present environments. Natural selection does not involve progress towards an ultimate goal. Evolution does not necessarily strive for more advanced, more intelligent, or more sophisticated life forms. Rapid environmental changes typically cause extinctions. In the s and s, efforts were made to merge Darwin's theory of natural selection, research in heredity, and understandings of the fossil records into a unified explanatory model.
Dobzhansky's work Genetics and the Origin of Species was an important step in bridging the gap between genetics and field biology. Mayr, on the basis of an understanding of genes and direct observations of evolutionary processes from field research, introduced the biological species concept, which defined a species as a group of interbreeding or potentially interbreeding populations that are reproductively isolated from all other populations.
The paleontologist George Gaylord Simpson helped to incorporate fossil research, which showed a pattern consistent with the branching and non-directional pathway of evolution of organisms predicted by the modern synthesis. The modern synthesis emphasizes the importance of populations as the unit of evolution, the central role of natural selection as the most important mechanism of evolution, and the idea of gradualism to explain how large changes evolve as an accumulation of small changes over long periods of time.
Evidence for evolution[ edit ] Fossil record[ edit ] Research in the field of paleontology, the study of fossils, supports the idea that all living organisms are related. Fossils provide evidence that accumulated changes in organisms over long periods of time have led to the diverse forms of life we see today.
A fossil itself reveals the organism's structure and the relationships between present and extinct species, allowing paleontologists to construct a family tree for all of the life forms on earth. Cuvier noted that, in sedimentary rock each layer contained a specific group of fossils.
General Biology/Introduction to Evolution - Wikibooks, open books for an open world
The deeper layers, which he proposed to be older, contained simpler life forms. He noted that many forms of life from the past are no longer present today.
As a result, the general idea of catastrophism has re-emerged as a valid hypothesis for at least some of the rapid changes in life forms that appear in the fossil records. A very large number of fossils have now been discovered and identified. These fossils serve as a chronological record of evolution. The fossil record provides examples of transitional species that demonstrate ancestral links between past and present life forms. The implication from such a find is that modern reptiles and birds arose from a common ancestor.
This can be done by comparing the structure of adult organisms in different species or by comparing the patterns of how cells grow, divide and even migrate during an organism's development. Embryology In some cases, anatomical comparison of structures in the embryos of two or more species provides evidence for a shared ancestor that may not be obvious in the adult forms.
General Biology/Introduction to Evolution
As the embryo develops, these homologies can be lost to view, and the structures can take on different functions. Part of the basis of classifying the vertebrate group which includes humansis the presence of a tail extending beyond the anus and pharyngeal slits.
Both structures appear during some stage of embryonic development but are not always obvious in the adult form. It was thought that human embryos passed through an amphibian then a reptilian stage before completing their development as mammals. The first stages of development are similar in broad groups of organisms. As development continues, specific features emerge from this basic pattern.
Vestigial structures Homology includes a unique group of shared structures referred to as vestigial structures. Vestigial refers to anatomical parts that are of minimal, if any, value to the organism that possesses them.Heredity: Crash Course Biology #9
These apparently illogical structures are remnants of organs that played an important role in ancestral forms. Such is the case in whales, which have small vestigial bones that appear to be remnants of the leg bones of their ancestors which walked on land.
A bat is a mammal and its forearm bones have been adapted for flight. Anatomical comparisons can be misleading, as not all anatomical similarities indicate a close relationship. Some mutations have no phenotypic effect but encourage subsequent mutations that move transpose data from one location in the data format genome to another location. Some mutations have no phenotypic effect but can encourage subsequent copying and duplication.
Redundancy can increase robustness or the tendency to resist alteration of the controlled function by subsequent mutation. Recombination in miosis can produce individuals having different combinations of genetic differences and therefore different phenotypic designs even though they are descendents of the same parents. Because of cascading, phenotypic differences resulting from recombination can be much larger than differences resulting from an individual propagatable mutation.
Inheritance is affected by the relative location locus of mutational differences in the genetic data structure genome due to the genetic linkage principle 1 — encourages group inheritance of linked mutational differences. Transposing of data affects this by changing relative location.
Natural selection selects combinations of genetic differences that improve performance, increasing prevalence of the underlying alleles.
The above brief summary grossly understates the sort of evolutionary process complexity that has emerged from study of inheritance mechanisms.
The sub-processes interact in very complex ways and tend to operate on long time frames even compared to evolutionary time standards. This affects the plausibility of group selection as described below. All of the steps appear to have evolvability benefits. Note that the complex concept is more powerful than the traditional concept because it allows for the possibility that a particular combination of mutational changes could result in a benefit even though each individual change, considered by itself, was mildly adverse.
Genes Genes specify organism phenotypic design and are a specific data structure within the overall genomic data structure mentioned above. The evolution of progressively more complex organisms has required the evolution of progressively more genes. The evolution of a new gene having a different function is, for many reasons, a particularly difficult step in the evolution process.
Indeed, genetics discoveries show that similar related organisms e.
How Genetics Discoveries Affect Evolution Theories
Their phenotypic differences are the result of relatively minor differences within the genes. This is the basis of the gene-oriented alternative evolutionary mechanics theories. Universality of Evolution Process Darwin and traditional evolutionary mechanics theory assumed that the evolution process is the same for all species. All species presumably were subject to mutational change and also to natural selection.
However, genetics discoveries disclosed gross differences in inheritance mechanisms that clearly affect propagation of mutational changes. In the latter case, phenotypic design is determined by the combined effect of both sets of genetic data.
Further, early genetics discoveries revealed that in many cases one state allele of a mutational difference dominated the design such that the opposite allele would have essentially no phenotypic effect unless both sets of genetic data contained the same recessive allele. Propagation of mutational changes is therefore very different in diploid organisms because an adverse mutational change that was recessive could propagate more readily than in the haploid case while a beneficial but recessive mutational change would propagate less well than in the haploid case.
Further analysis disclosed many other differences that plausibly affect propagation e. X or Y linking, mitochondrial DNA, etc. If the evolution process is different in different organisms potentially enormous complexity results.
Data acquired from study of bacteria is not necessarily applicable to complex organisms, etc. Perhaps mammals evolve in a different manner than plants? Are there many factors that influence the evolution process? Which species possess them?
From a traditional mechanics standpoint, the diploid inheritance mechanism appears to be a step backward. Propagation of beneficial changes is inhibited while propagation of adverse changes is encouraged. Why would a backward step evolve and be retained? Everybody agrees that diploid genomes and sexual reproduction are evolved designs. Is it possible that therefore organisms can evolve differences in their evolutionary processes? Can they evolve improvements in their evolutionary processes?
These questions lead to development of the evolvability alternative evolutionary mechanics theories. The potentially enormous increase in complexity exposed by rapidly advancing genetics science affects our scientific confidence regarding evolutionary mechanics.
Perhaps nobody really understands the details of evolutionary mechanics! A mutational change is the selectable property. However we now know that the digital nature of genetic data means that a genome either possesses or does not possess a given mutational difference generally a single nucleotide polymorphism or SNPa binary situation.
Any organism property that is more or less continuously variable in a population think bell-shaped curve must result from combining many genetic differences that simultaneously exist in that population and affect the given parameter. Further, virtually all potentially complex selectable properties e. The human population at large is now thought to currently contain millions of individual genetic differences, each presumably resulting from a different mutation in a different individual.
Therefore, in complex organisms, a selectable property is not the same as a mutational difference. This sort of logic tends to deemphasize the importance of individuals and individual possession of mutational changes relative to the importance of particular combinations of mutational changes where the underlying mutations are relatively widely dispersed in a population.
This in turn favors alternative evolution mechanics theories. Evolutionary Rapidity and Individual vs. Group Selection Everybody agrees that the design of anything is a compromise. Theorists agree that a group benefit could be a compromise with individual disadvantage. Functionally there is no difference between individual survival and group survival.
Either way, dead is dead, extinct is extinct. Therefore those who disagree with the group selection concept do so because of a timing issue. How would an individually disadvantageous design survive long enough to populate a group?