A friend sent me the below picture seeking my views. While the question is quite unscientific and I avoid ‘nontechnical’ discussions in most matters, particularly science, I find it apt to comment on this to address the doubts it may create in some minds. The question itself is ‘naïve’ because whether or not a species form is extant there is substantial evidence of their past existence through transitional fossils and other scientific means. While craftily designed to create doubts about the evolution, the question covers only the evolutionary history of primates, in particular the genus Homo, and the emergence of Homo sapiens as a distinct species of hominids (or "great apes"). The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, linguistics, evolutionary psychology, embryology and genetics.
Evolutionary biology is a strong and vigorous field of science. A theoretical structure that involves several basic mechanisms and is consistent with the patterns seen in nature; and there is abundant evidence demonstrating the action of these mechanisms as well as their contributions to nature. Hence, evolution is both a theory and a set of established facts that the theory explains. Like every other science, there is scientific debate about some aspects of evolution, but none of these debates appear likely to shake the foundations of this field. There exists no other scientific explanation that can account for all the patterns in nature, only non-scientific explanations.
THE QUESTION ABOUT THE MISSING LINK
From geological standards, we humans are a very young species. The average "lifespan" of a mammal species, measured by its duration in the fossil record, is around 10 million years. While hominids have followed a separate evolutionary path since their divergence from the ape lineage, around 7 million years ago, our own species (Homo sapiens) is much younger. Fossils classified as archaic Homo sapiens appear about 400,000 years ago, and the earliest known modern humans date back only 170,000 years. Our knowledge of human evolution continues to evolve fast, as new fossils continue to be discovered and described. Thirty five years ago, it was generally accepted that humans and the great apes last shared a common ancestor perhaps 16-20 million years ago, and that the separate human branch was occupied by only a few species, each evolving from the one before. Now we know, through a combination of new fossil finds and molecular biology, that humans and chimpanzees diverged as little as 7 million years ago, and that our own lineage is "bushy", with many different species in existence at the same time. The evidence on which scientific accounts of human evolution is based comes from many fields of natural science. The main source of knowledge about the evolutionary process has traditionally been the fossil record. However, with the development of genetics, DNA analyses now lead the body of evidence.
Darwin was remarkably prescient when he wrote, in 1871 "The Descent of Man", that humans had evolved in Africa and were closely related to the great apes (gorilla, chimpanzee, and orang-utan). The recent breakthroughs in genetics render resounding homage to his unparalleled genius. Current DNA evidence suggests that several haplotypes of Neanderthal origin are present among all non-African populations and Neanderthals and other hominids, such as Denisova hominin, may have contributed up to 6% of their genome to present-day humans. Anatomically modern humans evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 years ago. The transition to behavioural modernity with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago according to many anthropologists although some suggest a gradual change in behaviour over a longer time span. As there are thousands of fossils, mostly fragmentary, often consisting of single bones or isolated teeth with complete skulls and skeletons rare, this overview is not meant to be complete but the species evolutionary trajectory represents current consensus. If there is no clear scientific consensus the other possible classifications are indicated, that is the beauty of science – prospering through accommodating alternate views.
Homo rhodesiensis was the immediate ancestor of modern humans which evidently displaced the Neanderthals in Europe and the island 'hobbits' of Southeast Asia. Homo rhodesiensis evolved from Homo erectus about half a million years ago but still retains some primitive characteristics such as relatively thick bones and molars larger than modern humans.
Each time a certain mutation (Single nucleotide polymorphism) appears in an individual and is passed on to his or her descendants a haplogroup is formed including all of the descendants of the individual who will also carry that mutation. By comparing mitochondrial DNA which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve, must have lived around 200,000 years ago. We can detect the influence of evolution on the present-day human gene pool just as easily as we can view the development of our species' family tree.
This clearly means the whole idea of a simple "missing link" between humans and our ape cousins is false. There was no one, single moment when humans leapt from the trees to find a new existence on land. It happened gradually, over millennia, with different individuals from different species testing out what it would mean to live far from the protection of sheltering forests. Instead of thinking of transition stages as a "missing link" as exploited in the question, it would be more accurate to say the transition was a long chain, in which one kind of life shaded into the other very gradually.
To explain it in simpler terms, evolution reflects the growing up of an individual as a long exercise in intermediacy. For example, we do not just change to become adults at the stroke of midnight on our eighteenth birthday. Similarly, human evolution, from something like Australopithecus afarensis to Homo sapiens consisted of an unbroken series of parents giving birth to children who were mutating to evolve but yet each successive generation belonged in the same species as their parents. Hence there is no absence of intermediates in the process.
EVOLUTION ON THE MARCH
Evolution is a process that continues to march on. In the developed world, the combination of modern medicine, new agricultural and technological techniques, and cultural changes have considerably reduced the effects of natural selection. But in developing countries people are still exposed to these selection pressures, so this is where we look for evidence of evolutionary change e.g. the spread of alleles giving resistance to diseases such as malaria. In regions where malaria is endemic, anyone with a genotype giving resistance to malaria would be at an advantage in evolutionary terms, because they would be more likely to survive and reproduce, passing their advantageous combination of genes on to at least some of their children. The overlap between the geographic spread of malaria in Africa with the presence of the sickle-cell allele is an example: individuals heterozygous for this allele are at a selective advantage over unaffected individuals (and those homozygous for the allele) where malaria is present.
The "CCR5" gene is another example. This gene codes for CCR5, a surface protein on white blood cells that is also the docking site for the HIV virus. People homozygous for the 'delta 32' mutation in this gene are resistant to attack by HIV, and so they are at a selective advantage in populations where HIV infection is common. But surprisingly the mutation is most common in white Europeans, and very rare in other ethnic groups, including Africans, whereas AIDS is far more common in Africa than in Europe. The reason is that scientists have dated the origin of the delta 32 mutation to around 700 years ago, and the current hypothesis is that it provided protection against an epidemic disease of that time, perhaps plague or smallpox that were then common in Europe.
Obesity and all its related health problems, such as adult-onset (type II) diabetes, and cardiovascular disease, are most common in populations of people who have only recently taken up westernised lifestyles e.g. Nauru islanders, and the Pima Indians of North America. In both these groups, 70% of 60-year-olds have type II diabetes. In both populations, many people die before 60 of diseases related to diabetes and/or obesity. Because there are genotypes - beneficial for hunter-gatherer populations - that can predispose to these "western" diseases then it should be possible to see natural selection working upon them. In such populations we can predict strong selection against the genotypes that predispose individuals to "western" health problems. When Europeans and non-Europeans are matched for diet and lifestyle, the Europeans have a lower frequency of type II diabetes. This simply means that natural selection had already reduced European frequencies of those genotypes in previous centuries, as the western lifestyle was developing in Europe.
Another example of natural selection is the increased oxygen-carrying capacity in the blood. Tibetans living at 4,000m above sea level are exposed to lower partial pressure of oxygen, compared to people living at sea level. Researchers studying Tibetan villagers have discovered that women whose blood has a higher oxygen-carrying capacity tend to have more children that survive to adulthood. The highest villages in Tibet have a blood-oxygen concentration 10% higher than normal and examination of their family trees indicates that this difference is controlled by a single gene. Children of women with the apparent high-oxygen genotype are more likely to survive to have their own children, which suggests that this genotype has a significant reproductive advantage and so is likely to spread through the population – an example of evolution in progress.
There are numerous other pieces of recorded evidence of how the process of natural selection continues to work on all life, including us humans.
EVOLUTION AND FAITH
Science provides us with a compelling account and explanation of the changing life on Earth. Accepting evolutionary premises does not require faith at all, but is based on evidence. While religious faith can exist in spite of the evidence, science always follows the evidence. Whenever the evidence is not complete science withholds the judgment and continues to explore. Hence, in a body of scientific work there are always some pieces which are under scrutiny. The super-natural explanations based solely on faith lie outside of science, which can neither prove nor disprove miracles.
To the rational believer, science is a means of using the God-given gift of reason to understand how God has actually done things. At one point in history, believers used to think that the Sun revolved around the Earth, because they thought the Bible revealed this infallible truth. Science, however, revealed that the Earth revolves around the Sun. Although some believers resisted this discovery bitterly at first, mistaking their own interpretations for the infallible word of God, virtually all eventually came to understand that God simply could not have set things up the way they had thought. While believers will find the scientific view of the world enhanced and enriched by their religious beliefs, it is sheer folly to insist upon a point of doctrine, grounded in intuition and the authority of tradition, when scientific evidence indicates its falsity. The time will hopefully come when the creationists, like the geocentrists of old, set aside their dogmas and follow the light of reason so that they, too, may learn the great wonders science teaches of the universe and of God.
Having been born to Muslim parents, I can only allow myself the right to comment on the Quran. For me, the Quran and the Theory of Evolution are neither opposites nor alternatives to each other. Hence there is no direct clash. The Quran I read does not say that the life began with Adam. It says He chose him as His deputy on the earth. It says the man is born of lifeless object (semen). If the God can create man from a lifeless object then why can’t He start life from a lifeless object? If some folks do not want to accept certain parts of theory of evolution because they are not in conformity with certain interpretations of the Quran, then that is their prerogative and I will respect it but they should also refrain from disproving the matters of science in an unscientific manner just as I studied ‘Ilm ur Rijaal’ for years before allowing myself to discuss ‘Hadith’.
The Quran suffices for guidance in all moral and ethical and spiritual matters. However it is not a book of physics, chemistry, biology, medicine etc. the problem arise when people brand it as a repository of all that there is to know. Is it intended to have all that is to know? No, it spurs people to be good human beings, good Muslims and to explore. It urges them to think, reflect, and to continue to learn. When you set it up as carrying knowledge about everything then you set it up for rational failure. We should not needlessly set it up against the science because when the integrity of something deemed to be absolute is undermined, it never recovers.
To say that the man has design/physical defects does not prove that God did not create man. In fact according to all scriptures man and other things in the world are supposed to be imperfect. Only the God is perfect. Man is imperfect not only physically but also biologically, emotionally, and psychologically.
While we have addressed the issue of missing links, we need to let go of the myth that there were radical distinctions between early human species. Evolution is a chaotic process, and it will never stop being chaotic. Modern humans are continuing the process and in another million years, we may have evolved an entirely new way of getting around. If we have, it won't be because one day everybody woke up with a brand-new bone structure. It will be because over thousands of years, and millions of false starts, we slowly and irregularly transformed into a kind of human distinct from the ones who lived before and mutated to evolve.
The biogeographic evidence of evolution is now so incontrovertibly powerful that it cannot be wished away by pretending that the evidence does not exist. Each fossil discovered since Darwin’s time either actively supports or is compatible with evolution. Not a single fossil has been found to contradict evolution. And even if not a single fossil had ever been found, the evidence from molecular genetics and DNA in our time would force the conclusion that Darwin was right.