Encyclopedia of Evolution.pdf - Online Reading Center

Amino Acid Similarities among Vertebrates
for the β Chain of Hemoglobin
Number of Percentage of
amino acid differences, amino acid
out of , similarities
Animal compared to humans to humans
Human 0 100%
Gorilla 1 99%
Gibbon 2 98%
Rhesus monkey 8 94%
Dog 15 90%
Horse and cow 25 83%
Mouse 27 82%
Gray kangaroo 38 74%
Chicken 45 69%
Frog 67 54%
true bacteria, and eukaryotic nuclear DNA. Even though
archaebacteria and true bacteria look alike to most human
observers, they have numerous differences in their chemical
makeup and diverged from one another very early in the history
of life. Woese has accordingly classified all organisms
into three domains (Archaea, Eubacteria, and the domain
Eucarya that contains the protist, fungus, plant, and animal
kingdoms)—all on the basis of DNA comparisons (see tree
of life).
Origin of multicellular animals. The common ancestor
of multicellular animals is not known. By the time animals
show up in the fossil record, they have already differentiated
into many forms (see Burgess shale; Cambrian explosion;
Ediacaran organisms). Comparisons of DNA of
modern animals suggest that a wormlike organism lived in
the oceans a billion years ago. Dubbed the RFW or “roundish
flat worm,” it is the supposed ancestor of all bilaterally
symmetrical animals (see invertebrates, evolution of). If
the fossil of such an animal is ever found, it will not come as
a complete surprise to scientists, for the existence and even
the general appearance of this animal has been reconstructed
from DNA comparisons.
Pseudogenes in Six Species of Primates (from Friedberg and Rhoads)
DNA (evidence for evolution)
Evolutionary Patterns of Vertebrates
Evolution of hemoglobin. All vertebrates (except the hagfishes,
the most ancient branch) have hemoglobin (the red
protein that carries oxygen in blood) that consists of four
protein chains (two α and two β chains) surrounding a heme
group that has an iron atom in the middle. Over time, since
the origin of vertebrates, mutations have accumulated in the
gene for the β chain. As a result, different species of vertebrates
have different sequences of amino acids in the β chain.
Each vertebrate has a β chain amino acid sequence that most
closely resembles the sequence in the animals from which its
lineage diverged most recently. The further back in time the
lineages diverged, the less similar the amino acid sequences
are. The hemoglobin data confirm the evolutionary pattern
(see first table). The human β chain sequence is almost identical
to that of gorillas, a little less similar to that of the rhesus
monkey, even less similar to that of the dog, even less similar
to that of the kangaroo, even less to that of the chicken, and
least of all to that of the frog. Some invertebrates and even
plants also have hemoglobin, but it appears to have evolved
independently from simpler heme proteins, for which this
kind of comparison would not be meaningful.
Evolution of birds. Fifty million years ago birds had
teeth, but modern birds do not (see birds, evolution of).
Modern birds still have the gene for making a portion of their
teeth. This gene has lost its promoter and cannot be used. The
gene can be experimentally stimulated in chickens, resulting
in chickens with rudimentary teeth (see promoter).
Evolution of horses. The ancestors of modern horses had
three toes, unlike modern horses that have just one; occasionally,
mutations in DNA control sequences stimulate the
production of extra toes in modern horses (see horses, evolution
of).
Evolutionary Patterns of Primates
Humans and other primates. As noted above, species that
share a more recent common ancestor should share more
pseudogenes than species that have a common ancestor that
lived further back in the past. Evolutionary scientists Felix
Friedberg and Allen Rhoads have confirmed this pattern
among primates. They studied six human pseudogenes, for
which ages could be estimated. They then looked for these
pseudogenes in six primate species, and in the hamster (see
Estimated age Rhesus Capuchin
Pseudogene (millions of years) Human Chimp Gorilla Orangutan monkey monkey
α-Enolase Ψ1 11 • • •
AS Ψ7 16 • • •
CALM II Ψ2 19 • • • •
AS Ψ1 21 • • • • •
AS Ψ3 25 • • • • •
CALM II Ψ3 36 • • • • • •