The "Tree of Life" by Charles Darwin,
and by others up to the present time.
Phylogeny, and what drives the proliferation of species"
"Phylogeny" is a study of how species of life are related -- the genealogy of species. A main concept found in the theory of evolution is that, at any time in the past, species developed from earlier species as a result of natural selection influenced by environmental stressors, and by other factors.
A reviewer of Charles Darwin's book "Origin of the Species" wrote in 1859 that, according to the Theory of Evolution, humans developed from monkeys. Some modern-day creationists still quote that belief. Scientists have been denying it, without a lot of success, for over a century and a half. Rather, humans and, say, chimpanzees share a common ancestor. If one goes back in time, any two species of life will share a common ancestor: birds and bananas, for example.
"Natural selection" is sometimes associated with the term "survival of the fittest." This generates the impression in many people that evolution is driven by violence and the ability for a species to kill their competitors. The phrase "Nature [is] red in tooth and claw" is often heard. But "fittest" really means the ability of a particular group to adapt to its current environment and produce the largest number of healthy offspring. Among humans, this often has meant that tribes who have been more successful in organizing cooperative ventures have been the fittest.
The concept of natural selection has often been misinterpreted. One example involves some religious and social conservatives who believe that homosexuality is a chosen sexual orientation, and is not passed genetically. They note that lesbians and gays tend to have fewer children, when compared to heterosexuals. They conclude that if homosexual orientation were caused by genes, one might expect that natural selection would case it to become less common over time. Eventually, there would be no more homosexuals. Since they have survived for many millennia, some conservatives conclude that sexual orientation cannot be caused by genes; it must be chosen by the individual.
This reasoning overlooks the fact that genes can sometimes have a dual effect on reproduction: one can be positive and the other negative. Examples are:
Sickle-cell anemia. If both parents are carriers of the mutated gene for the disease, their children will inherit the illness. Their red blood cells will change shape. They will no longer be disc-shaped like that of a doughnut without a hole. They become crescent or sickle shape. The latter can cause blockages in blood vessels, preventing oxygen from reaching tissues properly, and causing organ failure. Life expectancy is shortened. Normally, the disease would be expected to gradually vanish from the gene pool. However, people who are carriers of sickle-cell anemia, without suffering from the disease itself, can experience a beneficial effect: immunity from malaria.
In the case of lesbians and gays, it has been found that their female relatives tend to have more children of their own. Thus whatever gene or combination of genes that cause homosexual orientation has a negative evolutionary effect because it lowers the number of children that they have. However, it also increases the number of children among the women in their extended family. Thus, homosexual orientation perseveres throughout history as a normal and natural sexual orientation.
An individual's DNA determines their appearance, design, capacity, etc. Sometimes a person's DNA structure will will experience the mutation of one or more of its genes, producing changes in the next generation. Usually the change will have no significant effect, or a negative effect. But sometimes, it enables the offspring to thrive better, and subsequently produce offspring who also cope better and reproduce in larger numbers. Changes in the environment can rapidly increase or decrease the rate of this change.
The tree of life:
Using the image of a tree with a trunk and branches to symbolize the evolution of species has a long history. It dates from the start of the 19th century. Using this symbol, the earliest form of life is located at the bottom of the trunk. The branches symbolize the individual species as they first appeared in the biological record, and later developed into other related species.
One principle that is implied by the tree of life is the concept of common ancestors. Any two leaves on a tree can be traced back to separate twigs, and then to one or two branches, and finally back to the trunk. Similarly, the ancestors of any two species can be traced back to a common ancestor species that they have in common. So, for example, humans and chimpanzees can be traced back to their common ancestor. So can whales and dinosaurs, or dogs and sponges, cats and fruit flies, etc.
There are statements widely circulating on the Internet that humans share 50% of their DNA with bananas, 1 or that we share 60% of our genes with fruit flies! 2
As Graham Lawton explained in his article "Uprooting Darwin's tree:"
"Ever since Darwin, the tree has been the unifying principle for understanding the history of life on Earth. At is base is "LUCA." the Last Universal Common Ancestor of all living things, and out of LUCA grows a trunk which splits again and again to create a vast, bifurcating tree. Each branch represents a single species, branching points are where one species becomes two. Most branches eventually come to a dead end as species go extinct, but some reach right to the top -- these are living species [present on Earth today]. The tree is thus a record of how every species that ever lived is related to all others right back to the origin of life." 3
Some early "trees of life" were:
1801:4 Augustin Augier, a French botanist, is believed to have published the first "tree of life" to demonstrate his concept of the relationships among plant species. He assumed that God created the various species at different times. Augier had deviated from the biblical creation story in the early chapters of Genesis which described a variety of plants and animals having been created within a few days.
1809:5 Jean-Baptiste Lamarck (1744-1829) was an early French evolutionist. He published the first tree of life that involved animals in his book Philosophie Zoologique. It was an inverted tree with worms at the top and mammals -- including humans -- at the bottom. He did not believe that all life evolved from a single organism; he believed that different species could be grouped into separate parallel lines that evolved over time from simple to complex forms.
He believed that acquired
characteristics could be passed down to the next generation. Thus, a man who became a blacksmith would develop large muscles, and would pass them on to his children. Many Communists adopted Lamarck's theories rather than those of Charles Darwin as the driving force behind evolution.
David Klinghoffer, writing for Evolution News and Views, commented on Joseph Stalin, the late Communist dictator of Russia, saying:
"In the 1930s, Stalin beat the drum for Lamarck with increased intensity. After 1945, the official evolutionary theory of Soviet Communism was represented by a Ukrainian agronomist and scientific fraud, Trofim Lysenko. Under the rule of Lysenkoism, dissenters from the favored evolutionary orthodoxy were subject to career-destruction, imprisonment, even death." 6