一本教會你“做對”題的6級閱讀書 day6 passage1
Passage 1 Studies Provide New Insight into Life Origin, Human Evolution 102
人類起源新學(xué)說 《衛(wèi)報》
[00:00]Studies provide new insight into life origin, human evolution
[00:07]A new study published in Proceedings of National Academy of Sciences
[00:12]rejects the theory that the origin of life stems
[00:16]from a system of self-catalytic molecules capable of experiencing
[00:21]Darwinian evolution without the need of RNA or DNA and their replication.
[00:28]The research, which was carried out with the participation of Mauro Santos,
[00:34]researcher of the Department of Genetics and Microbiology
[00:37]at Universitat Autnoma de Barcelona (UAB),
[00:41]has demonstrated that through the analysis of
[00:44]what some researchers name "compound genomes," these chemical networks
[00:50]cannot be considered evolutionary units because they lose properties
[00:56]which are essential for evolution when they reach a critical size
[01:00]and greater level of complexity.
[01:03]Also, the teeth of a 30,000-year-old child are shedding new light on
[01:08]the evolution of modern humans,
[01:11]thanks to research from the University of Bristol published
[01:15]in the Proceedings of the National Academy of Sciences.
[01:18]The teeth are part of the remarkably complete remains of a child
[01:23]found in the Abrigo do Lagar Velho, Portugal
[01:27]and excavated in 1998 and 1999 under the leadership of Professor Joo Zilho
[01:36]of the University of Bristol.
[01:38]Classified as a modern human with Neanderthal ancestry,
[01:43]the child raises controversial questions about how extensively Neanderthals
[01:49]and modern human groups of African descent interbred
[01:53]when they came into contact in Europe.
[01:57]The U.S. National Aeronautics and Space Administration (NASA)
[02:02]defines life as a "self-sustaining chemical system capable of
[02:08]Darwinian evolution." The scientific theories on the origin of life
[02:14]focus on two main ideas: one focuses on genetics
[02:19]with RNA or DNA replication as an essential condition for
[02:24]Darwinian evolution to take place --- and the other focuses on metabolism.
[02:31]It is clear that both situations must have begun
[02:35]with simple organic molecules formed by processes prior to the origin of life,
[02:42]as was demonstrated by the Miller-Urey experiment
[02:46](in which organic molecules were created from inorganic substances).
[02:52]The point in which these two theories differ
[02:55]is that the replication of RNA or DNA molecules is a far too complex process.
[03:03]Until now no seemingly reasonable chemical explanation exists for
[03:08]how these processes occurred. In addition,
[03:12]defenders of the second theory argued that the processes needed
[03:17]for evolution to take place depended on original metabolism, which in turn,
[03:23]eventually allows for adaptation and evolution
[03:27]without any molecular replication.
[03:31]In the first half of the 20th century,
[03:34]Alexander Oparin established the "Metabolism First" hypothesis
[03:39]to explain the origin of life.
[03:42]Oparin did not refer to RNA or DNA molecules since at that time
[03:49]it was not clear just how important the role of these molecules
[03:53]was in living organisms. However,
[03:57]he did form a solid base for the idea of self-replication
[04:01]as a collective property of molecular compounds.
[04:05]Science more recently demonstrated
[04:08]that sets of chemical components store information
[04:12]about their composition, which can be identically copied
[04:16]from an original and transmitted to their descendents.
[04:20]This has led to their being named "compound genomes".
[04:25]In other words, heredity does not require information
[04:31]in order to be stored in RNA or DNA molecules.
[04:35]These "compound genomes" apparently fulfil the conditions
[04:40]required to be considered evolutionary units,
[04:43]which suggests a pathway from pre-Darwinian dynamics to a minimum protocell.
[04:50]Researchers in this study nevertheless reveal
[04:53]that these systems are incapable of undergoing a Darwinian evolution.
[04:59]For the first time a rigorous analysis was carried out to
[05:04]study the supposed evolution of these molecular networks
[05:08]using a combination of numerical and analytical simulations
[05:13]and network analysis approximations. Their research demonstrated
[05:18]that the dynamics of molecular compound populations,
[05:22]which divide after having reached a critical size, do not evolve,
[05:28]since during this process the compounds lose properties
[05:31]which are essential for Darwinian evolution.
[05:35]Researchers concluded that this fundamental limitation of
[05:40]"compound genomes" should lead to caution towards theories
[05:44]that set metabolism first as the origin of life,
[05:47]even though former metabolic systems could have offered a stable habitat
[05:53]in which primitive RNA could have evolved.
[05:57]Researchers state that different Earth scenes prior to the origin of life
[06:02]can be considered. However, the basic property of life
[06:07]as a system capable of undergoing Darwinian evolution began
[06:12]when genetic information was finally stored and transmitted
[06:16]such as occurs in RNA and DNA.
[06:21]'Early modern humans', whose anatomy is basically similar to
[06:26]that of the human race today, emerged over 50,000 years ago
[06:31]and it has long been the common perception that little
[06:35]has changed in human biology since then.
[06:40]When considering the biology of late ancient humans
[06:45]such as the Neanderthals, it is thus common to compare them
[06:50]with living humans and largely ignore the biology of the early modern humans
[06:55]who were close in time to the Neanderthals.
[07:00]With this in mind, an international team, including Professor Zilho,
[07:05]re-analysed the type, number, and arrangement of a set of teeth of
[07:11]the Lagar Velho child, including all of its milk teeth
[07:15]and almost all of its permanent teeth, to see
[07:19]how they compared to the teeth of Neanderthals (later 12,000-year-old humans)
[07:25]and modern humans.
[07:28]Employing a technique, which uses x-rays to create cross-sections of 3D-objects,
[07:35]the researchers investigated the relative stages of formation of the teeth
[07:41]and the proportions of the teeth.
[07:45]They found that for a given stage of development of the cheek teeth,
[07:50]the front teeth were relatively delayed in their degree of formation.
[07:56]The teeth of the Lagar Velho child thus fit the pattern evident
[08:00]in the preceding Neanderthals
[08:02]and contrast with the teeth of later 12,000-year-old humans
[08:08]and living modern humans.
[08:11]Professor Zilho said:
[08:13]"This new analysis of the Lagar Velho child joins a growing body of
[08:19]information from other early modern human fossils found across Europe
[08:25]that shows these 'early modern humans' were 'modern'
[08:30]without being 'fully modern'. Human anatomical evolution continued
[08:36]after they lived 30,000 to 40,000 years ago."
