Heredity and Evolution

Humans did not evolve from monkeys. Humans are more closely related to modern apes than to monkeys, but we didn’t evolve from apes either. There existed a common ancestor for both the chimpanzees and humans, about 5-8 million years ago. Later, the two lineages diverged into two separate lineages. One of these lineages ultimately evolved into chimps and other apes, and the other evolved into early human ancestors called hominids.

When a population of a particular variant organism increases due to a survival advantage, it is the natural selection. In this case, green beetles cannot be seen by the crow and therefore, their population has grown compared to the red coloured beetles. Thus, natural selection pressure is exerted by crows.

Broccoli has been cultivated from wild cabbage by the method of artificial selection by the farmers. Green coloured flowering heads of broccoli are edible. The wild cabbage was bred and selected for this character to get broccoli.

Humans contain 22 pairs of autosomes and 1 pair of sex chromosomes. The female gamete or the egg consists of an “X” chromosome. If this is fertilised by a sperm containing “X” chromosome, the baby will have “XX” chromosome and will be a female. But if the egg is fertilised by a sperm containing “Y” chromosome, the baby will have “XY” chromosome and will be a male.

According to fossils discovered up to present time, the origin and evolution of man started from Africa. Regardless of where we have lived for the past few thousand years, we all come from Africa. The earliest members of the human species, Homo sapiens, can be traced there. Even our genetic footprints can be traced back to our African roots. According to various models and theories,modern humans originated in Africa and started to disperse through the world roughly 50,000 to 100,000 years ago. Such theories are based on the human fossil timeline records.

Humans have a total of 23 pairs of chromosomes, out of which 22 pairs are autosomes and 1 pair has sex chromosomes. The members of the autosomal pairs are homologous i.e., they are similar in shape and organisation. On the other hand, sex chomosomes or allosomes may be heterologous (in males) or homologous (in females).