Data Lineage Quotes

Tree of origin of humans and the four great apes based on DNA comparisons. Data points indicate how many millions of years ago species diverged. Chimpanzees and bonobos form a single genus: Pan. The human lineage diverged from the Pan ancestor about 5.5 million years ago. Some scientists feel that humans, chimpanzees, and bonobos are close enough to form a single genus: Homo. Since bonobos and chimpanzees split from each other after they split from us, about 2.5 million years ago, both are equally close to us. The gorilla diverged earlier, hence it is more distant from us, as is the only Asian great ape, the orangutan.

As also noted by Morris, empirical data from various lineages of fish and amphibians have shown, for instance, that more plastic clades tend to be more speciose than sister taxa of similar age but with less plasticity, due to a combination of greater opportunities to diversify and augmented evolvability of plastic features and thus of decreased risk of extinction. In addition, empirical studies show that even populations that derive from ancestors that were particularly overspecialized for a certain, very specific way of life, including parasitism, have successfully changed their behavior by becoming non-parasitic and displaying a morphology that is substantially different from that of their ancestors as seen for example in lamprey evolution. Morris argued that random variations arising in a population may decrease plasticity and that the plastically changed phenotype linked with the behavioral shift may be negatively affected. Therefore, these variants will be likely eliminated by selection, whereas variants that decrease plasticity in the direction of the plastic change will tend to be selected and spread through the population. This may lead to a situation in which the phenotype might appear similar across generations, but its plasticity is actually increasingly reduced until an environmental shift will no longer provoke phenotypic changes. As noted by Morris, Baldwin allowed for other non-mutually exclusive scenarios to occur, such as the rise of variants that increase plasticity in general, thus increasing the ‘fit’ between organisms and their environment and the degree to which evolution could be directed, thus leading to evolutionary trends.

Deeper phylogenetic relationships that are notoriously difficult to reconstruct with conventional sequence comparison methods are being resolved with miRNAs. The reason is that normal gene sequences continue to evolve after a lineage split, and, thus, the phylogenetic signal can erode by later evolution. In contrast, miRNAs stay put and, this, are like molecular fossils identifying related lineages. The only drawback is that miRNA inventories are expensive to determine and some of the data is based on the lack of certain miRNAs in certain species, which can always be a detection artifact.

Sexual dimorphism between species also helps to identify which mating pattern has been the species’ norm over evolutionary time (Baker & Bellis, 1995). For example, male chimpanzees’ testicle size is a whopping 3% of their total body weight, compared to .8% in human males and .02% in male gorillas. The promiscuous mating pattern of chimpanzees suggests that males with small testicles were selected against because they were unable to “wash out” the sperm of larger-testicled competitors. Among polygynous gorillas, one male controls a harem of females with little or no competition from other males, so there is little selection for large testicles and ejaculates. Male humans are between chimpanzees and gorillas in both testicle size and body size dimorphism; this supports the view that over evolutionary time humans have been at least mildly polygynous (Baker & Bellis, 1995). This point is further supported by genetic data concerning variation in Y chromosomes (genes passed only from fathers to sons), showing that just 19 male lineages have dominated in populating the world. One lineage within haplogroup C accounts for about 8% of the male population in Asia, suggesting that one male lineage, probably that of Gengis Khan, dominated mating within that region several hundred years ago.