16: Human Evolution The human species found in fossils in .NET framework

Drawing QR Code 2d barcode in .NET framework 16: Human Evolution The human species found in fossils

Paleontologists have found fossils for a large number of hominid species, including prehuman primates and human primates In fact, various hominid species have been identified from fossil remains, as Table 16-1 shows Note: The A or H in the species names is scientific shorthand Instead of writing Australopithecus, for example, scientists simply write A The term Australopithecus speaks to the origin of the fossil: southern Africa H, of course, stands for Homo, which means wise The name Homo sapiens means wise man

Table 16-1

A anamensis A afarensis (Lucy) A africanus A aethiopicus A boisei A robustus H rudolphensis H habilis H ergaster H erectus H heielbergensis H neanderthalensis H sapiens

Years on Earth (Based on Fossil Finds)

42 to 39 million years ago 36 to 29 million years ago 3 to 2 million years ago 27 to 23 million years ago 23 to 14 million years ago 18 to 15 million years ago 24 to 18 million years ago 23 to 16 million years ago 19 to 14 million years ago 19 to 03 million years ago (and possible 50,000 years ago) 600,000 to 100,000 years ago 250,000 to 30,000 years ago 100,000 years ago to today

As you can see, for most of the past 3 million or so years, multiple species of hominids have existed at any one time a situation that persisted until about 25,000 years ago In short, in the not-too-distant past, we shared Earth with human species other than our own

The dates in Table 16-1 indicate the years from which fossil specimens of each species have been recovered (For a review of how scientists determine the dates of fossils, see 2) But and this point is important the lack of fossil evidence doesn t necessarily mean that a species wasn t around longer than the time periods indicated, only that scientists haven t found it So even though the current dates indicate that a H habilis, for example, lived from 23 to 16 million years ago, if H habilis fossils dating from 1 million years ago are found, the dates would change (It s also why you see the range for H erectus and a note that this species also may have existed up to 50,000 years ago)

As 8 explains, a very useful way for determining whether two individuals are of the same or different species is to determine whether they can interbreed If the answer is yes, the individuals are of the same species; a no answer means, they are different species Obviously, this information isn t available for any of our fossil ancestors, so in this case, species names are simply a function of morphology, or body structure All the fossils that look the same are assigned to the same species This arrangement sounds easy enough until you consider that the fossil record is sparse and fossil remains of hominids usually are extremely incomplete part of the leg bone here, half a jaw there, part of the cranium somewhere else Complicating matters even more is the expectation of finding both juvenile and adult individuals, as well as males and females which may vary in size As a result, there s a fair bit of argument about whether a new find should be considered a new species or merely another representative of an existing species Using skull size and shape, jaw muscles, and limb length can help researchers distinguish between one hominid species and another, as follows: Ratio of forelimb to hind-limb length: Humans arms are proportionally much shorter than the arms of chimpanzees, and scientists find different fossil hominids with different arm-length ratios As bipedal locomotion (walking upright) developed, forelimb length shortened (If you want to get persnickety, as scientists tend to do, you can say that forelimbs aren t really arms until the organism is walking on its hind legs hence, the use of the term forelimbs) Forelimb length is a good way to evaluate which group a fossil belongs to because it s relatively constant for individuals of different ages The absolute lengths of forelimbs and hind-limbs change as the individual grows, but the ratio of the lengths is consistent over a range of individual sizes Skull shape: Humans have proportionally much larger brains than do the other apes