Today at 05:04 AM bluetrinity said this in Post #1
Can someone humor me and explain the theory of evolution to me in brief, concise and accurate terms? How does it explain the existence of human beings in the year 2003? Thanks in advance.
See below for Futuyma's discussion of evolution in brief. Humans, like all species, arise from changes in a previous species. The shorthand view of evolution is "descent with modification". Populations of organisms change over time in order to adapt to new environmental conditions. They change is caused by natural selection.
The key concept is that natural selection is an algorithm to get design. An algorithm is a process that can be followed by a servile dunce and come up with the result. Long division is an algorithm. Follow the steps and the right answer is guaranteed.
Well, follow the steps of natural selection and design is guaranteed. The environment sets design problems for a population of organisms and natural selection comes up with designs. For this you need:
1. Variations among the individuals of the population. Each variation is a potential design solution.
2. You need more individuals than the environment can support. Thanks to the rate of having offspring, this happens in natural populations all the time. There are always more individuals born than actually reproduce.
3. A competition among the individuals. This competition is not literal. For instance, plants in a desert are "competing" for the scarce water, but one plant isn't stealing water from another. Instead, there isn't water enough for
both of them to live, so the plant that can survive on less water does better. It is this competition that picks the good designs from among all the variations in the individuals.
4. Preservation of the good designs to the next generation. This is done by inheritance. What this means is that the next generation has new variations (new designs) that are modifications of the designs of the previous generation. Thus natural selection is
cumulative. Many small steps make a long journey.
Natural selection working on populations of organisms over 4.5 billion years, with millions of speciation events, produced humans and every other species on the planet.
A good intro book is
What Evolution IS by Ernst Mayr.
"Thus, evolution, in a broad sense is descent with modification, and often with diversification. Many kinds of systems are evolutionary ... In all such systems there are populations, or groups, of entities; there is variation in one or more characteristics among the members of the population; there is HEREDITARY SIMILARITY between parent and offspring entities; and over the course of generations there may be changes in the proportions of individuals with different characteristics within populations. This process consitutes descent with modification. Populations may become subdivided so that several populations are derived from a COMMON ANCESTRAL POPULATION. If different changes in the proportions of variant individuals transpire in te several populations,the populations DIVERGE, OR DIVERSIFY. ... All these properties of an evolutionary process pertain to populations of organisms, in which there is hereditary transmission of characteristics (based on genes, composed of DNA or, in a few cases, RNA), variation owing to mutation, and sorting of variation by several kinds of processes. Chief among these sorting processes are CHANCE (random variation in the survival or reproduction of different variants), and natural selection (consistent, nonrandom differences among variants in their rates of survival or reproduction). It is natural selection that causes adaptation -- improvement in function. Thus biological (or organic) evolution is change in the properties of populations of organisms , or groups of such populations, over the course of generations. ... Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportions of different forms of a gene within a population, such as the alleles that determine the different human blood types, to the alterations that led from the earliest organisms to dinosaurs, bees, snapdragons, and humans." Douglas Futuyma, Evolutionary Biology, (1999) pg 4.
