Evolution Test - 79

With an average cranial capacity of 1600 cc, Neanderthal's cranial capacity is notably larger than the 1400 cc average for modern humans, indicating that their brain size was larger. Cranial capacity of Australopithecus is 375 - 550 cc. Cranial capacity of Peking man is 1000 cc. Java man was characterized by a cranial capacity averaging 900 cc. 

Trilobites are a fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the stage of the Precambrian period around 521 million years ago, and they flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian period, all trilobite orders except Proetida died out. Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago.

The Pleistocene saw the evolution and expansion of our own species, Homo sapiens and by the close of the Pleistocene, humans had spread through most of the world. According to a controversial theory first proposed in the 1960s, human hunting around the close of the Pleistocene caused or contributed to the extinction of many of the Pleistocene large mammals. It is true that the extinction of large animals on different continents appears to correlate with the arrival of humans, but questions remain as to whether early human hunters were sufficiently numerous and technologically advanced to wipe out whole species. It has also been hypothesized that some disease wiped out species after species in the Pleistocene. The issue remains unsolved, perhaps the real cause of the Pleistocene extinction was a combination of these factors. So, genus Homo was identified in Pleistocene epoch.

Evolution of human beings has its origins in Africa as per the fossil records found there. By 1920s homind  fossils were discovered in Africa and in 1924, Raymond Dart  described Australopithecus africanus , the Tuang child as the ancestor to modern man and a transitional form between apes and humans.However, from then on the evolution of  homo species took on  giving rise to Homo habilis, Homo erectus, Homo neaderthalensis and Homo sapiens. However, there seems to be a transition between Homo erectus and Homo Sapiens in Africa. Further, studies on human genome ( y-chromosome DNA and mitochondrial DNA ) supported the African origin.  Evidence from autosomal DNA also supports the recent African origin.

Gymnosperms originated in the Paleozoic era. During Jurassic period, the second segment of Mesozoic era, gymnosperms had exposed seeds and showed wind distribution of pollen. This bisexual reproduction allowed for greater genetic combination. Hence, by the end of the Jurassic, the gymnosperms were dominant plants. Dinosaurs and flying pterosaurs dominated the ecosystems. First birds also appeared during this period which were evolved from branch of theropod dinosaurs.

Hardy-Weinberg equation is p$$^2$$ + 2pq + q$$^2$$ = 1. Here, p is the frequency of the "A" allele and q is the frequency of the "a" allele in the population. Thus, p$$^2$$ represents the frequency of the homozygous dominant genotype AA, q$$^2$$ is the frequency of the homozygous recessive genotype aa, and 2pq represents the frequency of the heterozygous genotype Aa. Further, it also states that the sum of the allele frequencies for all the alleles at the locus should be 1, so p + q = 1. According to the question, the frequency of AA is (p$$^2$$ = 0.25). Thus, the frequency of dominant allele = p = √.25 = 0.5. 

Palaeozoic era is also called as “era of ancient life”. It is divided into six periods which are namely Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian period. Cambrian period (520-505 million yrs ago) is marked by establishment of invertebrate phyla as well as earlier vertebrates and dominant trilobites. Ordovician period (505-430 million years ago) is marked by appearance of first vertebrates and fungi as well as major extinction of marine species. Silurian period (430-410 million years ago) marked by origin of jawed fishes, wingless insects and terrestrial vascular plants. Devonian period (410-360 million years ago) is marked by origin of amphibians and diversification and dominance of fishes on earth. Carboniferous period (360-285 million years ago) is marked by origin of first reptiles and arthropods as well as abundance of horsetails, fern and seed bearing plants. Permian period (285-250 million years ago) is marked by abundance of primitive reptiles and appearance of conifers. 

Devonian period (395 million years ago) of Palaeozoic era is also known as “age of fishes” and is marked by origin of amphibians and diversification and dominance of fishes on earth. Option B is incorrect. Mesozoic era (from 230 million years ago to 63 million yrs ago) is the era of medieval life and includes three periods namely, Triassic (225 million years), Jurassic (180 million years) and Cretaceous (135 million years). It is also known as age of reptiles. Triassic period is marked by appearance of first dinosaurs and mammals. The dinosaurs were small in size. Jurassic period is marked by diversification of dinosaurs; large dinosaurs dominated the earth. Cretaceous period is marked by appearance of archaic modern mammals, modern birds and teleost fishes as well as extinction of giant reptiles and toothed birds. Primitive birds were present in Mesozoic era. 

• Peking man, extinct hominin of the species Homo erectus, known from fossils found at Zhoukoudian near Beijing. They lived between 750,000 and 200,000 years ago.
• Homo heidelbergensis is an extinct species or subspecies of archaic humans in the genus Homo, which radiated in the Middle Pleistocene from about 700,000 to 300,000 years ago.
  
• Neanderthals are an extinct species or subspecies of archaic humans in the genus Homo, who lived within Eurasia from circa 400,000 until 40,000 years ago.
  
• Cro-Magnons had powerful bodies, which were usually heavy and solid with strong muscles. Unlike Neanderthals, which had slanted foreheads, the Cro-Magnons had straight foreheads, like modern humans. They lived 400,000 to 37,000 years ago.
  
• Hence Peking man$$\rightarrow$$ Heidelberg man$$\rightarrow$$ Neanderthal man$$\rightarrow$$ Cro-Magnon man is the correct order in the evolutionary history of man.
• So, the correct answer is 'Peking man$$\rightarrow$$ Heidelberg man$$\rightarrow$$ Neanderthal man$$\rightarrow$$ Cro-Magnon man'.