A horse Is a Horse, the Course, the Course

This illustration was developed in 1848, but it"s most likely that you recognize the animal it depicts together a horse. Although equines haven"t adjusted that much since this drawing was made, they have a long evolutionary history during which they adjusted significantly. Exactly how do we know? The prize lies in the fossil record.

You are watching: What is the principle of common descent

api/deki/files/18141/Horseevolution.png?revision=1&size=bestfit&width=462&height=561" />Figure \(\PageIndex2\): development of the Horse. The fossil record reveals how equines evolved. The lineage that led to contemporary horses (Equus) grew taller in time (from the 0.4 m Hyracotherium in early on Eocene to the 1.6 m Equus). This lineage likewise developed longer molar teeth and the degeneration that the outer phalanges top top the feet.

Fossils are a home window into the past. They administer clear proof that evolution has occurred. Scientists who find and study fossils are referred to as paleontologists. Exactly how do they use fossils to know the past? think about the instance of the horse, outlined in number \(\PageIndex2\). Fossils covering a period of much more than 50 million years display how the horse evolved.

The oldest steed fossils present what the earliest horses were like. Lock were just 0.4 m tall, or about the dimension of a fox, and they had 4 long toes. Other evidence shows they resided in wooded marshlands, wherein they probably ate soft leaves. Over time, the climate ended up being drier, and grasslands progressively replaced the marshes. Later fossils present that horses adjusted as well.

They became taller, i m sorry would help them watch predators while they fed in tall grasses. Eventually, they reached a elevation of about 1.6 m. They evolved a single big toe the eventually came to be a hoof. This would help them run swiftly and also escape predators. Your molars (back teeth) became longer and also covered with tough cement. This would permit them to grind difficult grasses and also grass seeds without wearing the end their teeth.

Comparative Anatomy

Figure \(\PageIndex3\): Mammals (such as cats and also whales) have homologous limb structures - with a different in its entirety look yet the very same bones. Insects (such together praying mantis and water boatman) additionally have homologous limbs. Cat legs and praying mantis legs are analogous - looking similar but from various evolutionary lineages.

Comparative anatomy is the study of the similarities and also differences in the structures of different species. Similar body parts may be homologous structures or analogous structures. Both administer evidence because that evolution.

Homologous structures are structures the are similar in related organisms since they were inherited indigenous a typical ancestor. These structures may or may not have the same duty in the descendants. Number \(\PageIndex3\) shows the upper appendages the several various mammals. Lock all have the same simple pattern the bones, although they now have various functions. Every one of these mammals inherited this simple bone pattern from a usual ancestor.

Analogous structures are structures that are comparable in unrelated organisms. The structures are comparable because they developed to execute the same job, not due to the fact that they were inherited from a usual ancestor. For example, the wings of bats and also birds, presented in the figure that follows, look comparable on the outside and have the very same function. However, wings evolved independently in the two groups of animals. This is apparent when you to compare the pattern of bones within the wings.

Comparative Embryology

Comparative embryology is the study of the similarities and differences in the embryos of various species. Similarities in embryos are likely to be proof of common ancestry. Every vertebrate embryos, for example, have gill slits and also tails. Every one of the embryos in figure \(\PageIndex4\), except for fish, lose their gill slits through adulthood, and some the them likewise lose their tail. In humans, the tail is lessened to the tail bone. Thus, similarities biology share together embryos may no longer be present by adulthood. This is why that is an important to to compare organisms in the embryonic stage.

Figure \(\PageIndex4\): Embryos of various vertebrates look much an ext similar 보다 the pets do at later stages that life. Rows I, II, and also III illustrate the advancement of the embryos that fish ~ above the far left, salamander, tortoise, chick, hog, calf, rabbit, and also human on the much right, indigenous the earliest to the latest stages.

Vestigial Structures

Structures choose the human being tail bone are dubbed vestigial structures. Development has diminished their size since the structures are no much longer used. The human appendix is one more example of a vestigial structure. It is a tiny remnant the a once-larger organ. In a remote ancestor, the was required to digest food, yet it offer no purpose in the human body today. Why carry out you think frameworks that room no much longer used shrink in size? Why could a full-sized, unused structure alleviate an organism’s fitness?

Comparing DNA

Darwin might compare only the anatomy and embryos of living things. Today, scientists deserve to compare your DNA. Similar DNA sequences room the strongest proof for evolution from a common ancestor. Look in ~ the diagram in number \(\PageIndex5\). The diagram is a cladogram, a branching diagram reflecting related organisms. Each branch represents the appearance of brand-new traits that different one group of biology from the rest. The cladogram in the number shows how humans and apes room related based upon their DNA sequences.

Figure \(\PageIndex1\): number \(\PageIndex5\): Cladogram of Humans and Apes. This cladogram is based on DNA comparisons. The shows exactly how humans are pertained to apes by descent from common ancestors. Human beings are most very closely related come chimpanzees and Bonobo (our usual ancestor existed many recently). We room less closely related to gorillas, and also even less carefully related come Orangutan.

invernessgangshow.netgeography of Camels: one Example

Today, the camel family contains different varieties of camels (Figure \(\PageIndex6\)). Every one of today’s camels room descended from the exact same camel ancestors. These ancestors stayed in North America about a million years ago.

See more: Which Of The Following Is Not A Strong Acid? (Or A Weak Electrolyte

Early phibìc American camels moved to various other places. Some went to eastern Asia via a soil bridge during the last ice age. A few of them do it all the means to Africa. Others went to south America by cross the Isthmus that Panama. Once camels reached these different places, they progressed independently. They progressed adaptations that suited them because that the certain environment wherein they lived. Through herbal selection, descendants of the original camel ancestors developed the diversity they have today.

Figure \(\PageIndex6\). Camel Migrations and Present-Day Variation. Members the the camel family now live in various parts the the world. Dromedary camels are found in Africa, Bactrian camels in Asia, and also Llamas in southern America. They differ from one one more in a variety of traits. However, they share straightforward similarities. This is because they all evolved from a common ancestor. What differences and also similarities carry out you see?