Human evolutionary genetics - Wikipedia
Great apes (humans, chimps, bonobos, gorillas and orangutans) there is no sharp line between humans and the rest of the animal kingdom. Tiny Genetic Differences between Humans and Other Primates Pervade the Genome The recent sequencing of the gorilla, chimpanzee and bonobo Yet that tiny portion of unshared DNA makes a world of difference: it. Humans, chimpanzees, gorillas, orangutans and their extinct ancestors form a So despite analyses of anatomy, the evolutionary relationships among many.
How closely are gorillas related to us? - Berggorilla & Regenwald Direkthilfe e.V.
The sequences of a protein say, hemoglobin from two organisms can be compared and the number of positions where the two sequences differ counted.
It was soon learned from such studies that for a given protein, the number of amino acid substitutions per year could--as a first approximation--be treated as constant.
This discovery became known as the "molecular clock. Using such reasoning, it has been estimated that the last common ancestor of humans and chimpanzees with whom we share 99 percent of our genes lived five million years ago. Going back a little farther, the Hominidae clade is 13 million years old.
If we continue farther back in time, we find that placental mammals are between 60 and 80 million years old and that the oldest four-limbed animal, or tetrapod, lived between and million years ago and the earliest chordates animals with a notochord appeared about million years ago.
Humans belong to each of these successively broader groups. How far back can we go in this way? If we try to trace all life on our planet, we are constrained by the earth's age of 4. The oldest bacteria-like fossils are 3. The question is whether at some point before this date a last common ancestor for all forms of life, a "universal ancestor," existed.
Over the past 30 years the underlying biochemical unity of all plants, animals and microbes has become increasingly apparent. All organisms share a similar genetic machinery and certain biochemical motifs related to metabolism.
It is therefore very likely that there once existed a universal ancestor and, in this sense, all things alive are related to each other.
Human evolutionary genetics
There are two mechanisms that remove alleles: With one or a combination of these mechanisms it is possible that in the proper environment, evolution may take place. In any case, evolution is defined as a change in the gene pool. This means that evolution is a population level phenomenon. Only groups of organisms evolve. An individual organism does not evolve. So when thinking of evolution, it is necessary to view population as a collection of individuals with different traits.
DNA is composed of four nucleotides making a double helix. When three species are fairly closely related to each other like human, chimpanzee and gorillathe trees obtained from DNA sequence data may not be congruent with the tree that represents the speciation species tree.
How closely are gorillas related to us?
The shorter internodal time span TIN the more common are incongruent gene trees. The effective population size Ne of the internodal population determines how long genetic lineages are preserved in the population.
A higher effective population size causes more incongruent gene trees. Therefore, if the internodal time span is known, the ancestral effective population size of the common ancestor of humans and chimpanzees can be calculated.
When each segment was analyzed individually, 31 supported the Homo-Pan clade, 10 supported the Homo-Gorilla clade, and 12 supported the Pan-Gorilla clade. Using the molecular clock the authors estimated that gorillas split up first 6.
The internodal time span is useful to estimate the ancestral effective population size of the common ancestor of humans and chimpanzees. A parsimonious analysis revealed that 24 loci supported the Homo-Pan clade, 7 supported the Homo-Gorilla clade, 2 supported the Pan-Gorilla clade and 20 gave no resolution. Additionally they took 35 protein coding loci from databases.
Of these 12 supported the Homo-Pan clade, 3 the Homo-Gorilla clade, 4 the Pan-Gorilla clade and 16 gave no resolution. This value is not as high as that from the first study Takahatabut still much higher than present day effective population size of humans.
Only a very tiny fraction of those fixed differences gave rise to the different phenotypes of humans and chimpanzees and finding those is a great challenge. The vast majority of the differences are neutral and do not affect the phenotype. All are thought to have played some part in human evolution.
Gene loss[ edit ] Many different mutations can inactivate a gene, but few will change its function in a specific way. Inactivation mutations will therefore be readily available for selection to act on.
Gene loss could thus be a common mechanism of evolutionary adaptation the "less-is-more" hypothesis. Genes involved in chemoreception and immune response are overrepresented.
Keratins are a major component of hairs. Humans still have nine functional type I hair keratin genes, but the loss of that particular gene may have caused the thinning of human body hair.
Based on the assumption of a constant molecular clock, the study predicts the gene loss occurred relatively recently in human evolution—less than years ago, but both the Vindija Neandertal and the high-coverage Denisovan sequence contain the same premature stop codons as modern humans and hence dating should be greater than years ago.
They estimated that the mutation that led to the inactivation a two base pair deletion occurred 2. The period that followed was marked by a strong increase in cranial capacitypromoting speculation that the loss of the gene may have removed an evolutionary constraint on brain size in the genus Homo. The loss of this gene is speculated to have reduced the lethality of bacterial infection in humans. Human-specific DNA insertions[ edit ] When the human genome was compared to the genomes of five comparison primate species, including the chimpanzee, gorilla, orangutan, gibbon, and macaque, it was found that there are approximately 20, human-specific insertions believed to be regulatory.
While most insertions appear to be fitness neutral, a small amount have been identified in positively selected genes showing associations to neural phenotypes and some relating to dental and sensory perception-related phenotypes.