Loren Eiseley in his "Darwin's Century" poses a very key question about human evolution. Namely, "Why have humans evolved [physically] so little while all sorts of life forms were evolving so fast around them?". In fact, he points out that we are not very different, in body plan, from our ape cousins.
Recent results from genetics indicate that, at the [protein coding] genomic level, we are only 2% different from our closest relative the Chimp. On the other hand, the evolution of hominid cranium capacity, as confirmed by the fossil record, was literally explosive. Cranium capacity being considered a proxy for brain capacity and function.
The recent discovery of fossil remains of a hominid dated at about 5.8 MYA (earliest hominid; for additional articles & stories: Google search: "Woldegabriel Haile-Selassie") providing clear evidence of bipedal posture, if confirmed, would shed considerable light on these issues.
First such a discovery would provide clear evidence that bipedalism preceded, by several million years, the rapid expansion of the human brain (last million years & specially last couple of hundred thousands of years).
Secondly it would indicate that bipedal, knuckle walking & brachiating apes co-evolved. Modifying the previous view of bipedal hominids being a much later evolution from the ape stock.
The question then is why did bipedalism arise so early in ape evolution? The answer, given by some scholars, is that the apes simultaneously branched out into specialist & generalist species.
The specialists leading to modern Chimps, Gorilla, Orang-outang, etc.. the generalists leading to several hominid lines of which Homo Sapiens Sapiens is today the only surviving relative.
If this conjecture, regarding the evolutionary pressures leading to the hominid lines, is correct it would, we believe, explain both the emergence of bipedalism & the progressive growth of hominid brain capacity.
In fact, a generalist life style puts a premium on being able to cover a larger territory, bipedalism with its greater speed and flexibility would be adaptive.
Similarly a generalist life style would require learning details about a larger and more varied territory, a greater variety of foods & techniques for finding & gathering them. Therefore greater brain capacity would be adaptive.
It has been discovered that related species' genomes are distinct shuffles of the genomic card deck. It seems that such shuffling is useful to reproductively separate budding sub-species from each other by interfering with interspecies lining up & matching of coding sequences in the zygote. This will, initially, reduce interbreeding success and eventually eliminate it altogether. Thus, eventually, as explained in Homo Pan divergence, the gene pool will split into separate gene pools free to follow independent evolutionary trajectories maximizing adaptation to distinct emerging niches.
An interesting case of species divergence is that of the separation between the Chimps (Pan) and the Homo lines. On May 17, 2006 Prof. David Reich of Harvard Medical School reported some startling findings concerning the divergence of the DNA for the Homo and Pan species. Please refer to the newspaper articles below, which, unfortunately, are neither very accurate nor clear.
The evidence considered by Prof. Reich is the number of different base pairs (BPs) in the corresponding segments of the two species DNA. The number of differences being proportional to the elapsed time from the two segments divergence in the speciation process. In fact, the rate with which successful structural or architectural DNA changes accumulate is linear or proportional to elapsed time (CMoD). In other words, the number of different BPs can be considered a molecular clock for the evolution of the two related species. What Prof. Reich found is that different DNA segments yield different elapsed time figures, with the earliest separation occurring somewhere between 6.3 MYA and 5.4 MYA and the most recent being only 1.2 MYA for X, the female sex chromosome. In other words, the separation of the human from the chimpazee species occurred over a period of about 4 million years in a rather complex process involving a number of cross species hybridizations. The X chromosome being the last one to diverge is not surprising at all since the molecular mechanisms for sperm egg interaction are highly species specific insuring the total reproductive isolation of recently separated species.
Here are some press reports re Prof. Reich findings:
Once the Homo gene pool separated, in a definitive way, from Pan's, both gene pools where free to independently evolve in directions of greater adaptation to the respective niches. In fact, as long as a gene pool corresponds to populations which are capable of some degree of hybridization it will exhibit some measure of central tendency. (See CMoD), or a sort of gravitational force, in gene coding space, which prevents subpopulations associated with the gene pool from freely migrating away. In fact, the offsprings genetic codes of a mating pair have to reside in a region of code space bounded by the greatest alleles difference of the two parents. The more genetically similar the parents, the smaller the code space region occupied by the offsprings.
Therefore, about 1.2 MYA the Homo species was free to evolve away from the Chimps into Homo Erectus. This new species, we know from the fossil record, exhibited an explosive growth of cranial capacity
The article cited below reports a recent, very intriguing, potentially seminal discovery concerning a gene mutation that seems to enable the ability to speak. The mutation in question enables a configuration of the mouth, throat etc. that favors the production of a very complex gamut of sounds.
A very intriguing aspect of this discovery is that this mutation dates back to 200,000 years ago. Interestingly enough, recent research on mitochondrial DNA (transmitted exclusively via the matrilineal descent) and Y [male] chromosome DNA (transmitted exclusively via the patrilineal descent) seems to confirm the emergence, at about the same time and out of Africa, of a population of Hominids of "modern" characteristics.
This population must have had a significant competitive advantage since it quickly (in 10,000 to 20,000 years) spread across the Earth & seems to have wiped out earlier Hominid forms. One can speculate that the enablement of a capability for advanced speech vocalizations would, under competitive pressures, quickly result in the emergence of forms of speech & the latter would produce a very significant competitive advantage.
In other words the emergence of Homo Sapiens 200,000 years ago very likely coincided with the emergence of speech in one Hominid line. This, if proved, would confirm that the essence of the "human" radiation or biological innovation is SPEECH.
More information can be found in : FOXP2 which hints at processes unleashed by the FOXP2 gene affecting both the oral cavity structures & muscles and some of the brain structures which deal with speech, such as the Broca area. While this article does not say explicitly so, the Evo Devo perspective of such development could be that FOXP2 codes for a protein which acts as a signal for the GenNets affecting the development of such areas.
A theory for the rapid evolution of the great Apes & Homo families could be based on the fact that in the last few million years our planet has rapidly cycled through glacial & warm periods. The interval between Ice Ages seems to be around 24,000 years. For instance the last Ice Age occurred 12,000 years ago & we are presumably near the maximum warming condition.
Environmental stresses that cycle through in tens of thousand years intervals instead of tens or hundreds of million years will place a great deal of adaptive premium on any mechanism that would cause species to rapidly adapt to the actual environmental conditions. In other words a world that goes, in a mere 12,000 years from polar to equatorial conditions, would favor problem solving ingenious creatures & their communities much more than a world where millions of years pass without an appreciable change of the environment.
Geology, in turn, seems to have the key to why our time is singular. Namely, it has been argued that the modern continental configuration (which emerged in the late Cretaceous 65 MYA) leads to a very unstable climate for the planet. We have one largish continent, Antarctica, under the South Pole, and a tight ring of continents (North America & Eurasia) around the North Pole.
Continental land masses under a Pole cause it to be much colder than an ocean. In fact an ocean would participate in a planet wide water circulation system that would keep the temperature of the Pole warmer. Some Pole cooling would take place in our North Pole since the polar ocean would have a restricted water circulation due to extensive fencing provided by North America & Eurasia.
This system has a tendency towards an Ice Age (primarily because of the South Pole) but probably is placed at the knife edge (I.e. it is in metastable equilibrium) because of the action of the North Pole. The 24,000 years or so periodicity of our present Ice Ages might suggest a link with the polar axes precession period which is 26,000 years.
In fact, the northern hemisphere will pass from a condition of maximum illumination (& warming) to a minimum one in 13,000 years (the same in a opposite way is true of the Southern hemisphere). When the North Pole is in the "warming" portion of the cycle the polar ocean probably liquifies and increases the temperature moderating currents, moving the planet away from an Ice Age. Precisely the obverse will occur in the second 13,000 year moving the planet from a benign warm period to a glaciation. The South Pole would not exert a countervailing effect since its land mass would be stuck on glaciation.
If these speculation are close to the mark, then one could conclude that our species, and its many present & extinct cousins, emerged now and not sooner or later, because of our planet present peculiar polar architecture. If one considers that plate tectonics are essentially thermal processes similar to those in a boiling pot & that these processes are random in a very profound sense (they are chaotic systems) one reaches the very sobering conclusion that the emergence of the human species is not only NOT a foreordained conclusion of evolution, but if the magma eddies had gone in different but equally likely way, we might not have emerged at all!
While the above are our personal speculations, it is a fact that the consensus view with regard to evolution is that it does not run in any preordained way. Or put it in another way if one had a thousand planets all with identical conditions, the thousand evolutionary processes would not replicate each other.
Therefore it is true that modern Science has redimensioned mankind to be NOT central in space, after Galileo time, and in our time NOT central in time, in the sense that we are not the apex of evolution or its end all. The only way to cultivate an exaggerated view of mankind role is to cultivate ignorance or obscurantism.
The only functions, attributes or features that appear in evolution are those which are "adaptive". I.e. required to "succeed". Success, in turn, is strictly the ability to transmit many copies of one's genes to the next generation.
In other words, what matters is reproductive success. The individual has to be fit to live long enough to reproduce. It must also succeed in attracting one or more mates to insure reproduction. The female of the pair, as the bearer of the embryo in mammalian species, has to be physically fit enough to nurture the offspring.
An important corollary of these facts is that sexual selection can be as powerful, or even more powerful, a selective pressure than either the physical environment or competition. In other words, sex is central to what mammals and thus humans are!
Sexual selection is probably responsible for the emergence of much beauty in the world. It certainly is the reason behind the evolution of many of the fantastic displays in birds, such as flamboyant feather coloring, or beautiful songs.
This means that if some characteristic arises it MUST have been adaptive vis a vis some competitive pressure OR some environmental factor OR sexual selection criterion which were operative at the time of selection.
If the factor ceases to be operative or decreases in pressure the engendered adaptive feature(s) will become noisy in the sense of being loaded with mutations. That is genetic noise.
The issue of the extraordinarily rapid evolution of the very large human intellectual faculties is an intriguing one. It would greatly increase the human race self knowledge to understand what were the reasons for the emergence of this extraordinary set of features. After all very many successful species get along with far less mental power.
The power of sexual selection factors in evolution can be illustrated by studying the "Cosmic Joke". By Cosmic Joke we mean the joke played by evolution on the human race. Namely, that men and women are profoundly and irremediably different. So different that one sex can not possibly see the world the way the other sees it.
The differential sexual selection arises simply from the fact that the two sexes have vastly different abundances of reproductive cells. Women having thousands of eggs. Men having billions of sperms.
In addition to this important difference there is also the difference in effort or investment the two sexes have to make to have an offspring carrying some of their genes to the next generation. Males, specially in primitive or wild state cultures contributing a modest effort.
Women, on the other hand, must commit a major biological (pregnancy) and nurturing effort. Given these significant differences, it would be truly extraordinary were the two sexes to follow similar reproductive strategies.
Simple observation shows that indeed they do not. Men, by and large, by instinct, are drawn towards promiscuous strategies of trying to seduce as many women as they can.
Women, on the other hand, follow the diametrically opposite strategy of trying to enter into long term relationships & generally opting for stability & security.
The Cosmic Joke is the source of untold human suffering, specially for the females, but evolution does not care for the happyness of the individual, or at least that is not something that is directly optimized. What is optimized is survival of the group.
Probably the most important implication of this arrangement is that women's physical fitness, during the child bearing phase, is far more important than a man's. We believe this is the fundamental reason why men's were evolved to attribute a disproportionate weight to physical fitness & beauty. So femminists' "objectivation" is Nature's insistence that men select fit mothers for their future children.
A key puzzle of human evolution is what was the actual mechanism exercising the adaptive pressure?
Our personal opinion is that it was sexual selection. It is well known that in most land animals the males, which are more expendable, engage in, sometimes lethal, competitions for breeding rights. Also in the case of many bird species the males are endowed, specially during the mating season, with flamboyant displays.
The point is that in all these animals the female chooses and THEREFORE EXERTS CONSIDERABLE SELECTIVE PRESSURE. It is not difficult to see that in modern human beings the "peacock feathers" are artistic & intellectual abilities.
In other words, we think that women have, over the eons, made us, both men & women, much smarter or gifted. This may also explain why we evolved such apparently "useless" skills as singing and music making.
They are very much NEEDED if you want to send your genes into the next generation. we believe that the instability of the climate & our generalist life style resulted into conditions that made a "female" liking of intellectual & artistic skills (more & more sophisticated brain power) adaptive.
Such a selective process, in fact, would indeed result into an explosive rate of evolution of the cranial & brain capacity, similar to the breeder ability to alter livestock in a matter of few generations to acquire commercially desirable traits.
Every human culture, at all stages of cultural development, has formulated some form of creation story offering an explanation of how the world, its plants & animals and human beings came to be. Most of these creation credos have been evolved over untold generations and are credited with Vox Populis Vox Dei characteristics. Such credos serve many purposes, besides explaining the world to inquiring minds, such as providing guidance on good & evil, sexual taboos, dietary prescriptions, etc..
Each culture assumes that their credo is the absolute revealed truth, while the culture also assumes to be the center of the world and the gem of the Universe. A corollary of these beliefs is that other cultures' credos are blasphemous heresies and their practitioners children of the Evil One to be exterminated or converted to the true faith at all costs. This state of provincialism & intolerance was viable until the last few centuries when different people & cultures were geographically contained and isolated, but it started to break down in the late 15th century when the age of great explorations started.
This state of affairs is totally unacceptable today (2006) when 600 million human beings are a few clicks and less than 60 msec away from each other. The short term "solution" evolved since the 70's splitting the faith from the political aspects of a society's credo, while being a step in the right direction, creates its own problems as witnessed by the culture wars in the US and EU. Furthermore, it is totally ineffective in preventing or mitigating the religious war that, for instance, Islamic groups are waging against the West & its interests.
The solution, fashionable in the West, of considering that credos could be considered private matters to be settled upon by free individuals, does not wash since, for example, the definition of what is considered criminal activity is dependent on the society predominant beliefs, that is its majority espoused credo. For instance, during the 1945 to 1989 Cold War two societies, the US & the USSR, faced each other with virtually diametrically opposed ethical systems arising respectively from the Judeo-Christian credo & the Marxists' historical materialism. The two society's heroes were villains or criminals in the other society. US entrepreneurs being considered anti social thieves if they had been in the USSR. Similarly, most of the USSR's government and political cadres would have been considered mafia-like criminals in the US.
It is therefore, impossible to have a common and respected law unless most members of a society share a common credo. At the same time we live now in a world which URGENTLY needs to evolve a planet wide law. This, in turn, implies that we urgently need to evolve a Universal Credo system. This is, of course, an incredibly difficult task. There are only two ways to get there: coercion and conviction. The trouble with the former is that in the nuclear age it will most likely result in unacceptable destruction. Conviction, while being politically very difficult, can only succeed if the planet wide credo is based of TRUTH that is on Science. The good news is that Science has already evolved very effective structures and methods for arriving to planet wide agreement & support of scientific results, validation or refutation of theories. In other words, scientists already accept, by and large, the body of scientific truths independently of their cultural, national or other associations.
A good example of both propositions is the current world wide debate regarding the legalities of stem cell research. It shows, first of all, that there is no world wide consensus on whether obtaining stem cells from even embryos to be discarded is a legitimate activity. It also shows that Science is the only source of information that could help come up with a rational & universal decision. For example, human embryology shows that stem cells capable of differentiating into any of human cell types can be obtained during the first two weeks of embryonic development and that no brain cells are on hand until the 23rd day of development. This last bit of information, if widely diffused & understood could lead to a universal ruling. In fact, it is very likely that the overwhelming majority of people would agree that no human life is present if there is no trace of a brain. The key point being not the particular break, but having corroborated factual information on which to base a cultural/political decision, will enhance the universal acceptability of such decision.
One should also keep in mind that the popularization of science's advances, specially in cosmology and biology, are eroding the credibility of all traditional credos, specially among the college educated classes. This phenomenon is virtually universal. This is particularly harmful since in most cases such popularizations are not done well & tend to mechanize the portrayed world. A good example of this effect are the Marxist theory of history, and many of the quasi scientific theories that abound in the social & psychological sciences. The total effect of poor quasi-science is to destroy or at least weaken traditional credos while replacing them with simplistic and reductionistic theories of reality and the place mankind occupies in it. This, in turn, is resulting in a world-wide erosion of traditional mores and their replacement by ego centered behavior and politics which are turning mankind in the latest mass extinction agent.
It is therefore urgent that we get our cultures on a different track, but this is no easy task. In fact we face at least the following difficulties:
Some possible remedies or strategies to overcome these factors are: