Lamarck and the Giraffes
Darwin was not the first to propose a theory explaining the variety of life on earth. One of the most widely accepted theories of evolution in Darwin’s day was that proposed by Jean-Baptiste de Lamarck.
In the 18th century, Lamarck had proposed that acquired traits were inherited and passed to offspring. For example, he stated that giraffes had long necks because they were constantly reaching for higher leaves while feeding. This theory is referred to as the “law of use and disuse,” or as we might say, “use it or lose it.” According to Lamarck, giraffes have long necks because they constantly use them.
We now know that Lamarck’s theory was wrong. This is because acquired changes (changes at a “macro” level in somatic cells) cannot be passed on to germ cells. For example, if you were to lose one of your fingers, your children would not inherit this trait.
What Evidence Supports Evolution?
Nature “selects” which living things survive and reproduce. The evidence to support the theory of evolution can be found in various science fields.
Paleontology (the study of fossils) – Has revealed the great variety of organisms (most of which are extinct) and the major lines of evolution.
Biogeography (the study of the distribution of plants and animals in the environment) – Scientists have found related species in widely separated regions of the world. For example, Darwin observed that animals in the Galapagos have traits similar to those of animals on the mainland of South America. One possible explanation for these similarities is a common ancestor.
Embryology (the study of the development of an organism) – All vertebrate embryos look alike in the early stages of development. They all show fish-like features called gill slits – including humans.
Comparative anatomy (the study of the anatomy of various animals) – scientists have discovered that some animals have similar structures that serve different functions. For example, a human’s arm, a cat’s leg, a bat’s wing, and a whale’s fin are all the same appendages. However, they have evolved to serve a different purpose.
These structures, called homologous structures, also point to a common ancestor. In contrast, some animals have features with the same function but different structure. For example, a bat’s wing and an insect’s wing have the same function (both used to fly), but have evolved independently of one another. These are called analogous structures.
Another example of an analogous structure is the eye. Although scallops, insects, and humans all have eyes, the three different types of eyes are thought to have evolved independently of one another.
Molecular Biology – The most convincing evidence of all is the similarity at the molecular level. Today, scientists can examine the nucleotide and amino acid sequences of different organisms. From these analyses, we have discovered that organisms that are closely related have a greater proportion of sequences in common when compared to distantly related species. For example, most of us don’t look like chimpanzees. However, by some estimates, almost 99% of our genetic code is identical to that of a chimp.
…Continued in Part 3