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The sperm, the egg, and the fetus all have "life".
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That is incorrect. Observe:
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Conventional definition: Often scientists say that life is a characteristic of organisms that exhibit the following phenomena:
1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.
2. Organization: Being composed of one or more cells, which are the basic units of life.
3. Metabolism: Consumption of energy by converting nonliving material into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
4. Growth: Maintenance of a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter. The particular species begins to multiply and expand as the evolution continues to flourish.
5. Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present.
6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun or an animal chasing its prey.
7. Reproduction: The ability to produce new organisms. Reproduction can be the division of one cell to form two new cells. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from at least two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.
http://en.wikipedia.org/wiki/Life#Definitions
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Two sperms cant reproduce with each other. No matter how old they get, or how long they are allowed to develop.
But a fetus will eventually mature and be capable of reproduction. So even a zygote fits the definition above. But a sperm does not.