Paleontology

Paleontology is simply the study of prehistoric life. It studies the evolutionary history of organisms to improve our understanding of past life. By one estimate, the number of species that ever lived is 10 billion, so paleontologists have a lot of work to do.


Fossils are a significant source of evidence for evolution. Here's some of the evidence we see:

  • Fossils in geologically younger rock layers are similar or identical to existing organisms.
  • The older the rock layer, the more the fossils differ from today's organisms.
  • Gaps in the fossil record have been gradually filled in as more discoveries are made.
  • Transitional fossils that are found largely have the features that evolution predicted they would have. They show features that are part-way between earlier fossils and later ones.
  • Fossils of any species are only found in rock layers younger than their ancestor species. As the great evolutionary biologist J.B.S. Haldane once remarked, “If we found a rabbit in a rock layer from the Jurassic era, we would consider abandoning the theory of evolution.”

Developmental Biology

Developmental biology studies how organisms develop into mature adults from single cells. One especially well-studied area is how vertebrate embryos develop. They pass through various stages that are remarkably similar. All vertebrates have certain common features, some of which are seen only in the embryo stage. The following four main features shared by all chordates—the large group that includes vertebrates— are not found in other groups of animals. 

  • the presence of a rod-like structure called the notochord
  • a dorsal, hollow nerve cord
  • a post-anal tail
  • pharyngeal pouches or slits, sometimes referred to as pharyngeal gill slits.

Being vertebrates, humans have all of these features at some time during our development. What is interesting is the great differences in what the final result turns out to be. Here are some examples:

  • There are some small chordates called lancelets that still have a notochord even as adults. It gives rigidity to their bodies. In humans, the notochord present in early stages is seen only as remnants that form the disks in our spinal column.
  • In fish, the pharyngeal structures become supports for their gills. In humans, these same structures form a portion of our inner ear that we use for hearing things.
  • Vertebrates have five digits in their very early stage of development. In cattle and pigs, these get reduced and fused to produce a cloven hoof. In horses they reduce to a single-digit hoof. They become wings in birds, and hands or feet in humans.

Anatomy and Physiology

Anatomy and physiology, in biology, is an organism's shape and structure. We can group organisms together according to their shape and structure. For example, we put organisms with six legs in the group Insecta and those with eight in the group Arachnida. We can further classify organisms by whether or not they have membranous wings. This happens to divide Insecta into smaller groups. If we keep doing this, we end up with a hierarchy of groups within groups.


If we ask why things are this way, evolution offers a very simple answer. Evolution explains this as organisms inheriting traits from their ancestors. Bats and birds both have wings, but their wings have different structures, so the wings didn't come from the same ancestor. However, the bones in bat and bird wings are just different arrangements of similar bones found in human arms, dog legs, and horse legs. Evolution explains all this very simply. All these animals share a common ancestor that had all these bones. Such similarities are called homologies.


Molecular Biology

Genetics is the study of DNA and how DNA affects organisms. This includes, of course, genes. In general, organisms that look similar on the outside have similar genes. An observer can easily see that humans are more similar to orangutans, less similar to rats, and even less similar to daisies. The number of genes we have in common usually matches our physical appearance.


Let's compare how similar human genes are to the genes of other animals, restricting ourselves to genes that produce proteins.

  • Yeast - 45% identical
  • Fruit flies - 60% identical
  • Chickens - 90% identical
  • Rabbits - 95% identical
  • Chimpanzees - 98% identical


This is why fruit flies make excellent study subjects for research in human genetics. We can learn about 60% of our genetic information by studying a species that is plentiful, cheap, easy to breed, and prolific. We have a simple explanation for how all this happened. It's called evolution, and the contingencies of evolution explain a lot of the oddities we find in genetics.