Were the dramatic changes in a result of cooked food, or was Turkana Boy as his species became hunters instead of hunted, and the stone tools softened up the meat and plant foods so that he did not need to chew as much? Wrangham co-authored a that began with . It concluded that food processing, cooking in particular, accounted for the effect. Cooked food versus raw food and the number of neurons that can be supported in a brain has been . The primary reason why Wrangham’s hypothesis was initially dismissed was that archeological evidence for fires that long ago is almost nonexistent. When was published, the earliest evidence with wide acceptance only supported fires , where Israel is today, which is more than a million years after Wrangham’s estimated timeframe. Wrangham did what all bold scientists do: he made falsifiable predictions. If it turned out that no evidence of early fires was ever found, his hypothesis could begin looking shaky.
In the 1990s, Wrangham began to develop his Cooking Hypothesis, which he more fully elucidated in , published in 2009. Wrangham marshaled numerous lines of evidence to support his hypothesis, which was widely pilloried by his colleagues. Wrangham conceded that the archeological record was scarce for the early control of fire, but he countered that evidence for early fires would rarely survive. Most caves last a quarter million years or so; they are made from soft stone, and the geological dynamics that create caves also destroy them. Also, early humans, just like gorillas and chimpanzees today, and even early hunter-gatherers, would have been constantly on the move, never sleeping in the same place twice. If the first fires were made in the African woodlands and grasslands, the evidence would not survive for long, just as the remnants of today’s hunter-gatherer fires on the African savanna quickly disappear. The gist of Wrangham’s Cooking Hypothesis is this:
It also states that, given that mitochondria have some striking similarities to bacteria, the most parsimonious hypothesis for mitochondrial evolution is that of endosymbiosis. ( deals with some aspects of multiple-occurence/convergent endosymbiosis).
How strong is the evidence for either of these leading hypotheses (perhaps there is a review article)? Is there evidence that is overwhelmingly in favour of endosymbiosis?
There is one more evidence to support the endosymbiosis theory:There is this observation that organelles that are less numerous in a cell have retained more of their genome compared to those with the organelles that are surplus numbers (eg. plastids vs mitochondria). This is called the Limited Transfer Window Hypothesis which reasons that the organelle to nuclear gene translocation would have happened because of organellar injury and the likelihood of a cell tolerating one is higher if there are more number of organelles.
Endosymbiotic theory was first proposed by Konstantin Mereschkowski in 1910. He worked as a botanist and through his work, found the ideas described above to be plausible. It would be more than 50 years before the microbiological evidence discovered by Lynn Margulis in 1967 would help to substantiate the theory.
In the Endosymbiotic theory, the idea is that a eukaryotic mitochondrion evolved from an autotrophic bacterium that had been engulfed by the eukaryotic cell. This cell was able to arise when an anaerobic prokaryote lost its cell wall because it was unable to use oxygen for energy. The flexible membrane underneath began to grow and then fold in on itself, which led to the creation of a nucleus and additional internal membranes.
Endosymbiotic theory, which is often referred to as “symbiogenesis,” is an evolutionary theory that attempts to explain the origin of eukaryotic cells. It is a hypothesis which essentially postulates that prokaryotes were what gave rise to the first eukaryotic cells and, if true, would rank amongst the most important evolutionary events in our history.
When looking at Endosymbiotic theory through modern science, it appears that there were extensive mergers and rearrangements of genetic material in several of the original mitochondrial chromosomes. In looking at lice at this level, it shows that the symbiotic relationships in the ancient world could have formed to work together in a way that could create the building blocks of life as we know it on our planet today.
This relationship serves as a model for evidence of endosymbiotic theory in practice today in nature. It was first discovered in 1973 and its cell membranes exhibit unusual features that include membrane lipids that are mostly present in the symbiotic prokaryotes of eukaryotic cells.
Major groups of protists include protozoan – for example, amoebas, algae and slime molds. Major evolutionary acquisition of protists is through endosymbiosis which results in eukaryotic organelles, and colony behavior which results in multicellular organisms. Endosymbiotic hypothesis is an attempt to account for the major evolutionary leap from prokaryotes to protists, the first eukaryotes. The hypothesis proposes a larger prokaryote ingested a smaller prokaryote such as a nutshell, organelles such as mitochondria and chloroplasts therefore arose. Much evidence comparing similarities of mitochondria to prokaryotes supports this idea.
The moon rocks retrieved by astronauts are still being tested, as new experiments and hypotheses are devised. In 2012, which resulted from testing moon rocks for the ratios (both are stable isotopes), and it has brought into question the hypothesis that the Moon was formed by a planetary collision more than four billion years ago. The titanium ratio was so much like Earth’s that a collision with Earth forming the Moon has been questioned (as very little of the hypothesized colliding body became part of the Moon). The collision hypothesis will probably survive, but it may be significantly different from today’s hypothesis. , as well as , and their ages confirm that geologists have derived, and meteorite dates provide more evidence that our .
Those interrelated and often mutually reinforcing lines of evidence have made many scientific findings difficult to deny. The ever-advancing scientific toolset, and the ingenuity of scientists developing and using them, and particularly the multidisciplinary approach that scientists and scholars are increasingly using, have made for radical changes in how we view the past. Those radical changes will not end any time soon, and what follows will certainly be modified by new discoveries and interpretations, but I have tried to stay largely within the prevailing findings, hypotheses, and theories, while also poking into the fringes and leading edges somewhat. Any mistakes in fact or interpretation in what follows are mine.